{"history":[{"id":"ac3ae573-94ba-44be-883f-11f311a1ee5c","wordChanged":"leaves","newWord":":::summary\n**Vickers Hardness:** 950HV \n**Vickers Hardness Ref:** https://www.journalmt.com/pdfs/mft/2018/04/16.pdf \n:::\n\n# \n**Chromium** is a [chemical element](https://bliptext.com/articles/chemical-element); it has [symbol](https://bliptext.com/articles/symbol-chemistry) **Cr** and [atomic number](https://bliptext.com/articles/atomic-number) 24.\nIt is the first element in [group 6](https://bliptext.com/articles/group-6-element).\nIt is a steely-grey, [lustrous](https://bliptext.com/articles/luster-mineralogy), hard, and brittle [transition metal](https://bliptext.com/articles/transition-metal).\nChromium is valued for its high [corrosion](https://bliptext.com/articles/corrosion) resistance and [hardness](https://bliptext.com/articles/hardness).\nA major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form [stainless steel](https://bliptext.com/articles/stainless-steel).\nStainless steel and [chrome plating](https://bliptext.com/articles/chrome-plating) ([electroplating](https://bliptext.com/articles/electroplating) with chromium) together comprise 85% of the commercial use.\nChromium is also greatly valued as a [metal](https://bliptext.com/articles/metal) that is able to be highly [polished](https://bliptext.com/articles/polishing) while resisting [tarnishing](https://bliptext.com/articles/tarnish).\nPolished chromium reflects almost 70% of the [visible spectrum](https://bliptext.com/articles/visible-spectrum), and almost 90% of [infrared light](https://bliptext.com/articles/infrared).\nThe name of the element is derived from the [Greek](https://bliptext.com/articles/ancient-greek) word χρῶμα, chrōma, meaning [color](https://bliptext.com/articles/color), because many chromium compounds are intensely [color](https://bliptext.com/articles/color)ed.\nIndustrial production of chromium proceeds from [chromite](https://bliptext.com/articles/chromite) ore (mostly FeCr2O4) to produce [ferrochromium](https://bliptext.com/articles/ferrochromium), an iron-chromium alloy, by means of [aluminothermic](https://bliptext.com/articles/aluminothermic-reaction) or [silicothermic reactions](https://bliptext.com/articles/silicothermic-reaction).\nFerrochromium is then used to produce alloys such as stainless steel.\nPure chromium metal is produced by a different process: [roasting](https://bliptext.com/articles/roasting-metallurgy) and [leaching](https://bliptext.com/articles/leaching-metallurgy) of chromite to separate it from iron, followed by reduction with [carbon](https://bliptext.com/articles/carbon) and then [aluminium](https://bliptext.com/articles/aluminium).\n[Trivalent](https://bliptext.com/articles/trivalent) chromium (Cr(III)) occurs naturally in many foods and is sold as a [dietary supplement](https://bliptext.com/articles/dietary-supplement), although there is insufficient evidence that dietary chromium provides nutritional benefit to people.\nIn 2014, the [European Food Safety Authority](https://bliptext.com/articles/european-food-safety-authority) concluded that research on dietary chromium did not justify it to be recognized as an essential [nutrient](https://bliptext.com/articles/nutrient).\nWhile chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called \"[hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium)\", is toxic and [carcinogenic](https://bliptext.com/articles/carcinogenic).\nAccording to the European Chemicals Agency (ECHA), [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) that is used in industrial electroplating processes is a \"substance of very high concern\" (SVHC).\n\n# Physical properties\n\n## Atomic\nGaseous chromium has a ground-state [electron configuration](https://bliptext.com/articles/electron-configuration) of [ [Ar](https://bliptext.com/articles/argon)] 3d5 4s1.\nIt is the first element in the periodic table whose configuration violates the [Aufbau principle](https://bliptext.com/articles/aufbau-principle).\nExceptions to the principle also occur later in the periodic table for elements such as [copper](https://bliptext.com/articles/copper), [niobium](https://bliptext.com/articles/niobium) and [molybdenum](https://bliptext.com/articles/molybdenum).\nChromium is the first element in the 3d series where the 3d electrons start to sink into the core; they thus contribute less to [metallic bonding](https://bliptext.com/articles/metallic-bonding), and hence the melting and boiling points and the [enthalpy of atomisation](https://bliptext.com/articles/enthalpy-of-atomisation) of chromium are lower than those of the preceding element [vanadium](https://bliptext.com/articles/vanadium).\nChromium(VI) is a strong [oxidising agent](https://bliptext.com/articles/oxidising-agent) in contrast to the [molybdenum](https://bliptext.com/articles/molybdenum)(VI) and [tungsten](https://bliptext.com/articles/tungsten)(VI) oxides.\n\n## Bulk\nChromium is the third hardest element after [carbon](https://bliptext.com/articles/carbon) ([diamond](https://bliptext.com/articles/diamond)) and [boron](https://bliptext.com/articles/boron).\nIts [Mohs hardness](https://bliptext.com/articles/mohs-scale-of-mineral-hardness) is 8.5, which means that it can scratch samples of [quartz](https://bliptext.com/articles/quartz) and [topaz](https://bliptext.com/articles/topaz), but can be scratched by [corundum](https://bliptext.com/articles/corundum).\nChromium is highly resistant to [tarnishing](https://bliptext.com/articles/tarnish), which makes it useful as a metal that preserves its outermost layer from [corroding](https://bliptext.com/articles/corrosion), unlike other metals such as [copper](https://bliptext.com/articles/copper), [magnesium](https://bliptext.com/articles/magnesium), and [aluminium](https://bliptext.com/articles/aluminium).\nChromium has a [melting point](https://bliptext.com/articles/melting-point) of 1907 °C (3465 °F), which is relatively low compared to the majority of transition metals.\nHowever, it still has the second highest melting point out of all the [period 4 elements](https://bliptext.com/articles/period-4-element), being topped by [vanadium](https://bliptext.com/articles/vanadium) by 3 °C (5 °F) at 1910 °C (3470 °F).\nThe [boiling point](https://bliptext.com/articles/boiling-point) of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest [boiling point](https://bliptext.com/articles/boiling-point) out of the [Period 4](https://bliptext.com/articles/period-4) [transition metals](https://bliptext.com/articles/transition-metal) alone behind [copper](https://bliptext.com/articles/copper), [manganese](https://bliptext.com/articles/manganese) and [zinc](https://bliptext.com/articles/zinc).\nThe [electrical resistivity](https://bliptext.com/articles/electrical-resistivity-and-conductivity) of chromium at 20 °C is 125 [nanoohm](https://bliptext.com/articles/ohm)-[meters](https://bliptext.com/articles/meter).\nChromium has a high [specular reflection](https://bliptext.com/articles/specular-reflection) in comparison to other transition metals.\nIn [infrared](https://bliptext.com/articles/infrared), at 425 [μm](https://bliptext.com/articles/micrometre), chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 [μm](https://bliptext.com/articles/micrometre) before rising again to 90% at 4000 [μm](https://bliptext.com/articles/micrometre).\nWhen chromium is used in [stainless steel](https://bliptext.com/articles/stainless-steel) alloys and [polished](https://bliptext.com/articles/polishing), the specular reflection decreases with the inclusion of additional metals, yet is still high in comparison with other alloys.\nBetween 40% and 60% of the visible spectrum is reflected from polished stainless steel.\nThe explanation on why chromium displays such a high turnout of reflected [photon](https://bliptext.com/articles/photon) waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties.\nChromium has unique magnetic properties; it is the only elemental solid that shows [antiferromagnetic](https://bliptext.com/articles/antiferromagnetic) ordering at room temperature and below.\nAbove 38 °C, its magnetic ordering becomes [paramagnetic](https://bliptext.com/articles/paramagnetic).\nThe antiferromagnetic properties, which cause the chromium atoms to temporarily [ionize](https://bliptext.com/articles/ionization) and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the [lattice periodicity](https://bliptext.com/articles/crystal-structure).\nThis is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers.\nFrom here, the frequency-dependent [relative permittivity](https://bliptext.com/articles/relative-permittivity) of chromium, deriving from [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations) and Chromakopia By, Tylerthecreator chromium with a high infrared and visible light reflectance.\n# [Sample of chromium metal | upload.wikimedia.org/wikipedia/commons/a/a1/Chromium.jpg]\n\n### Passivation\nChromium metal in air is [passivated](https://bliptext.com/articles/passivation-chemistry): it forms a thin, protective surface layer of chromium oxide with the [corundum](https://bliptext.com/articles/corundum-structure) structure.\nPassivation can be enhanced by short contact with [oxidizing acids](https://bliptext.com/articles/oxidizing-acid) like [nitric acid](https://bliptext.com/articles/nitric-acid).\nPassivated chromium is stable against acids.\nPassivation can be removed with a strong [reducing agent](https://bliptext.com/articles/reducing-agent) that destroys the protective oxide layer on the metal.\nChromium metal treated in this way readily dissolves in weak acids.\nThe surface [chromia](https://bliptext.com/articles/chromium-iii-oxide) Cr2O3 scale, is adherent to the metal.\nIn contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued [rusting](https://bliptext.com/articles/rust).\nAt room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward [diffusion](https://bliptext.com/articles/atomic-diffusion) of metal ions across the scale.\nAbove 950 °C volatile [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) CrO3 forms from the chromia scale, limiting the scale thickness and oxidation protection.\nChromium, unlike iron and nickel, does not suffer from [hydrogen embrittlement](https://bliptext.com/articles/hydrogen-embrittlement).\nHowever, it does suffer from nitrogen [embrittlement](https://bliptext.com/articles/embrittlement), reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.\n\n## Isotopes\nNaturally occurring chromium is composed of four stable [isotopes](https://bliptext.com/articles/isotope); 50Cr, 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% [natural abundance](https://bliptext.com/articles/natural-abundance)).\n50Cr is [observationally stable](https://bliptext.com/articles/stable-nuclide), as it is theoretically capable of [decaying](https://bliptext.com/articles/radioactive-decay) to [50Ti](https://bliptext.com/articles/isotopes-of-titanium) via [double electron capture](https://bliptext.com/articles/double-electron-capture) with a [half-life](https://bliptext.com/articles/half-life) of no less than 1.3 years.\nTwenty-five [radioisotopes](https://bliptext.com/articles/radioisotope) have been characterized, ranging from 42Cr to 70Cr; the most stable radioisotope is 51Cr with a half-life of 27.7 days.\nAll of the remaining [radioactive](https://bliptext.com/articles/radioactive) isotopes have half-lives that are less than 24 hours and the majority less than 1 minute.\nChromium also has two [metastable](https://bliptext.com/articles/metastable) [nuclear isomers](https://bliptext.com/articles/nuclear-isomer).\nThe primary [decay mode](https://bliptext.com/articles/decay-mode) before the most abundant stable isotope, 52Cr, is [electron capture](https://bliptext.com/articles/electron-capture) and the primary mode after is [beta decay](https://bliptext.com/articles/beta-decay).\n53Cr is the [radiogenic](https://bliptext.com/articles/radiogenic) decay product of 53[Mn](https://bliptext.com/articles/manganese) (half-life 3.74 million years).\nChromium isotopes are typically collocated (and compounded) with [manganese](https://bliptext.com/articles/manganese) isotopes.\nThis circumstance is useful in [isotope geology](https://bliptext.com/articles/isotope-geology).\nManganese-chromium isotope ratios reinforce the evidence from [26Al](https://bliptext.com/articles/aluminium-26) and 107[Pd](https://bliptext.com/articles/palladium) concerning the early history of the [Solar System](https://bliptext.com/articles/solar-system).\nVariations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies.\nHence 53Cr provides additional evidence for [nucleosynthetic](https://bliptext.com/articles/nucleosynthesis) processes immediately before coalescence of the Solar System.\n53Cr has been posited as a proxy for atmospheric oxygen concentration.\n\n# Chemistry and compounds\nChromium is a member of [group 6](https://bliptext.com/articles/group-6-element), of the [transition metals](https://bliptext.com/articles/transition-metal).\nThe +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.\n# [The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide | upload.wikimedia.org/wikipedia/commons/c/c3/Chromium///in///water///pourbiax///diagram.png]\n\n## Common oxidation states\n\n### Chromium(0)\nMany Cr(0) complexes are known.\n[Bis(benzene)chromium](https://bliptext.com/articles/bis-benzene-chromium) and [chromium hexacarbonyl](https://bliptext.com/articles/chromium-hexacarbonyl) are highlights in [organochromium chemistry](https://bliptext.com/articles/organochromium-chemistry).\n\n### Chromium(II)\nChromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air.\nWater-stable [chromium(II) chloride](https://bliptext.com/articles/chromium-ii-chloride) that can be made by reducing chromium(III) chloride with zinc.\nThe resulting bright blue solution created from dissolving chromium(II) chloride is stable at neutral [pH](https://bliptext.com/articles/ph).\nSome other notable chromium(II) compounds include [chromium(II) oxide](https://bliptext.com/articles/chromium-ii-oxide), and [chromium(II) sulfate](https://bliptext.com/articles/chromium-ii-sulfate).\nMany chromium(II) carboxylates are known.\nThe red [chromium(II) acetate](https://bliptext.com/articles/chromium-ii-acetate) (Cr2(O2CCH3)4) is somewhat famous.\nIt features a Cr-Cr [quadruple bond](https://bliptext.com/articles/quadruple-bond).\n# [Chromium(II) carbide (Cr3C2) | upload.wikimedia.org/wikipedia/commons/e/eb/Chromium///carbide///Cr3C2.JPG]\n\n### Chromium(III)\nA large number of chromium(III) compounds are known, such as [chromium(III) nitrate](https://bliptext.com/articles/chromium-nitrate), [chromium(III) acetate](https://bliptext.com/articles/chromium-iii-acetate), and [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium(III) can be obtained by dissolving elemental chromium in acids like [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid) or [sulfuric acid](https://bliptext.com/articles/sulfuric-acid), but it can also be formed through the reduction of chromium(VI) by [cytochrome](https://bliptext.com/articles/cytochrome) [c7](https://bliptext.com/articles/cytochrome-c).\nThe ion has a similar radius (63 [pm](https://bliptext.com/articles/picometer)) to (radius 50 [pm](https://bliptext.com/articles/picometer)), and they can replace each other in some compounds, such as in [chrome [alum](https://bliptext.com/articles/alum)](https://bliptext.com/articles/chrome-[alum](https://bliptext.com/articles/alum)) and [alum](https://bliptext.com/articles/alum).\nChromium(III) tends to form [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) complexes.\nCommercially available [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) hydrate is the dark green complex [CrCl2(H2O)4]Cl.\nClosely related compounds are the pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.\nIf anhydrous violet [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) is dissolved in water, the violet solution turns green after some time as the chloride in the inner [coordination sphere](https://bliptext.com/articles/coordination-sphere) is replaced by water.\nThis kind of reaction is also observed with solutions of [chrome alum](https://bliptext.com/articles/chrome-alum) and other water-soluble chromium(III) salts.\nA [tetrahedral](https://bliptext.com/articles/tetrahedral-molecular-geometry) coordination of [chromium(III)](https://bliptext.com/articles/chromium-iii) has been reported for the Cr-centered [Keggin](https://bliptext.com/articles/keggin-structure) anion [α-CrW12O40]5–.\n[Chromium(III) hydroxide](https://bliptext.com/articles/chromium-iii-hydroxide) (Cr(OH)3) is [amphoteric](https://bliptext.com/articles/amphoterism), dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form.\nIt is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), a stable oxide with a crystal structure identical to that of [corundum](https://bliptext.com/articles/corundum).\n# [Anhydrous chromium(III) chloride (CrCl3) | upload.wikimedia.org/wikipedia/commons/3/3b/Chromium%28III%29-chloride-purple-anhydrous-sunlight.jpg]\n\n### Chromium(VI)\n[Chromium(VI) compounds](https://bliptext.com/articles/hexavalent-chromium) are oxidants at low or neutral pH.\n[Chromate](https://bliptext.com/articles/chromate-and-[dichromate](https://bliptext.com/articles/chromate-and-dichromate)) anions and [dichromate](https://bliptext.com/articles/chromate-and-dichromate) (Cr2O72−) anions are the principal ions at this oxidation state.\nThey exist at an equilibrium, determined by pH:\nChromium(VI) oxyhalides are known also and include [chromyl fluoride](https://bliptext.com/articles/chromyl-fluoride) (CrO2F2) and [chromyl chloride](https://bliptext.com/articles/chromyl-chloride).\nHowever, despite several erroneous claims, [chromium hexafluoride](https://bliptext.com/articles/chromium-hexafluoride) (as well as all higher hexahalides) remains unknown, as of 2020.\n[Sodium chromate](https://bliptext.com/articles/sodium-chromate) is produced industrially by the oxidative roasting of [chromite](https://bliptext.com/articles/chromite) ore with [sodium carbonate](https://bliptext.com/articles/sodium-carbonate).\nThe change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of [potassium chromate](https://bliptext.com/articles/potassium-chromate).\nAt yet lower pH values, further condensation to more complex [oxyanions](https://bliptext.com/articles/oxyanion) of chromium is possible.\nBoth the [chromate and dichromate](https://bliptext.com/articles/chromate-and-dichromate) anions are strong oxidizing reagents at low pH:\nThey are, however, only moderately oxidizing at high pH:\nChromium(VI) compounds in solution can be detected by adding an acidic [hydrogen peroxide](https://bliptext.com/articles/hydrogen-peroxide) solution.\nThe unstable dark blue [chromium(VI) peroxide](https://bliptext.com/articles/chromium-vi-peroxide) (CrO5) is formed, which can be stabilized as an ether adduct.\n[Chromic acid](https://bliptext.com/articles/chromic-acid) has the hypothetical formula.\nIt is a vaguely described chemical, despite many well-defined chromates and dichromates being known.\nThe dark red [chromium(VI) oxide](https://bliptext.com/articles/chromium-vi-oxide), the acid [anhydride](https://bliptext.com/articles/anhydride) of chromic acid, is sold industrially as \"chromic acid\".\nIt can be produced by mixing sulfuric acid with dichromate and is a strong oxidizing agent.\n# [Chromium(VI) oxide | upload.wikimedia.org/wikipedia/commons/1/1e/Chrom%28VI%29-oxid.jpg]\n# [Sodium chromate (Na2CrO4) | upload.wikimedia.org/wikipedia/commons/5/51/Chroman///sodn%C3%BD.JPG]\n\n## Other oxidation states\nCompounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate.\nThe only binary compound is the volatile [chromium(V) fluoride](https://bliptext.com/articles/chromium-v-fluoride) (CrF5).\nThis red solid has a melting point of 30 °C and a boiling point of 117 °C.\nIt can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure.\nThe peroxochromate(V) is another example of the +5 oxidation state.\n[Potassium peroxochromate](https://bliptext.com/articles/potassium-tetraperoxochromate-v) (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures.\nThis red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.\nCompounds of chromium(IV) are slightly more common than those of chromium(V).\nThe tetrahalides, [CrF4](https://bliptext.com/articles/chromium-iv-fluoride), [CrCl4](https://bliptext.com/articles/chromium-iv-chloride), and CrBr4, can be produced by treating the trihalides with the corresponding halogen at elevated temperatures.\nSuch compounds are susceptible to disproportionation reactions and are not stable in water.\nOrganic compounds containing Cr(IV) state such as chromium tetra t-butoxide are also known.\nMost chromium(I) compounds are obtained solely by oxidation of electron-rich, [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) chromium(0) complexes.\nOther chromium(I) complexes contain [cyclopentadienyl](https://bliptext.com/articles/cyclopentadienyl) ligands.\nAs verified by [X-ray diffraction](https://bliptext.com/articles/x-ray-diffraction), a Cr-Cr [quintuple bond](https://bliptext.com/articles/quintuple-bond) (length 183.51(4) pm) has also been described.\nExtremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.\n# [Chromium compound determined experimentally to contain a Cr-Cr quintuple bond | upload.wikimedia.org/wikipedia/commons/6/60/5-fold///chromium.png]\n\n# Occurrence\nChromium is the 21st most [abundant element in Earth's crust](https://bliptext.com/articles/abundance-of-elements-in-earth-s-crust) with an average concentration of 100 ppm.\nChromium compounds are found in the environment from the [erosion](https://bliptext.com/articles/erosion) of chromium-containing rocks, and can be redistributed by volcanic eruptions.\nTypical background concentrations of chromium in environmental media are: atmosphere <10 ng/m3; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg.\nChromium is mined as chromite (FeCr2O4) ore.\nAbout two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers.\nUntapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.\nAlthough rare, deposits of [native](https://bliptext.com/articles/native-metal) chromium exist.\nThe [Udachnaya Pipe](https://bliptext.com/articles/udachnaya-pipe) in Russia produces samples of the native metal.\nThis mine is a [kimberlite](https://bliptext.com/articles/kimberlite) pipe, rich in [diamonds](https://bliptext.com/articles/diamond), and the [reducing environment](https://bliptext.com/articles/redox) helped produce both elemental chromium and [diamonds](https://bliptext.com/articles/diamond).\nThe relation between Cr(III) and Cr(VI) strongly depends on [pH](https://bliptext.com/articles/ph) and [oxidative](https://bliptext.com/articles/oxidative) properties of the location.\nIn most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L is Cr(VI).\n# [Crocoite (PbCrO4) | upload.wikimedia.org/wikipedia/commons/a/ac/Crocoite///from///Tasmania.jpg]\n# [Chromite ore | upload.wikimedia.org/wikipedia/commons/0/00/Chromit///1.jpg]\n\n# History\n\n## Early applications\nChromium minerals as pigments came to the attention of the west in the eighteenth century.\nOn 26 July 1761, [Johann Gottlob Lehmann](https://bliptext.com/articles/johann-gottlob-lehmann-scientist) found an orange-red mineral in the [Beryozovskoye mines](https://bliptext.com/articles/beryozovskoye-deposit) in the [Ural Mountains](https://bliptext.com/articles/ural-mountains) which he named Siberian red lead.\nThough misidentified as a [lead](https://bliptext.com/articles/lead) compound with [selenium](https://bliptext.com/articles/selenium) and [iron](https://bliptext.com/articles/iron) components, the mineral was in fact [crocoite](https://bliptext.com/articles/crocoite) with a formula of PbCrO4.\nIn 1770, [Peter Simon Pallas](https://bliptext.com/articles/peter-simon-pallas) visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a [pigment](https://bliptext.com/articles/pigment) in [paints](https://bliptext.com/articles/paint).\nAfter Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region.\nCrocoite would be the principal source of chromium in pigments until the discovery of [chromite](https://bliptext.com/articles/chromite) many years later.\nIn 1794, [Louis Nicolas Vauquelin](https://bliptext.com/articles/louis-nicolas-vauquelin) received samples of crocoite [ore](https://bliptext.com/articles/ore).\nHe produced [chromium trioxide](https://bliptext.com/articles/chromium-vi-oxide) (CrO3) by mixing crocoite with [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid).\nIn 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.\nVauquelin was also able to detect traces of chromium in precious [gemstones](https://bliptext.com/articles/gemstone), such as [ruby](https://bliptext.com/articles/ruby) and [emerald](https://bliptext.com/articles/emerald).\nDuring the nineteenth century, chromium was primarily used not only as a component of paints, but in [tanning](https://bliptext.com/articles/tanning-leather) salts as well.\nFor quite some time, the crocoite found in Russia was the main source for such tanning materials.\nIn 1827, a larger chromite deposit was discovered near [Baltimore](https://bliptext.com/articles/baltimore), United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.\nThis made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of [Bursa](https://bliptext.com/articles/bursa), Turkey.\nWith the development of metallurgy and chemical industries in the Western world, the need for chromium increased.\nChromium is also famous for its reflective, metallic luster when polished.\nIt is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by [electroplating](https://bliptext.com/articles/electroplating).\nChromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.\n# [The red color of rubies is due to trace amounts of chromium within the corundum. | upload.wikimedia.org/wikipedia/commons/c/c4/Cut///Ruby.jpg]\n\n# Production\nApproximately 28.8 million metric tons (Mt) of marketable chromite ore was produced in 2013, and converted into 7.5 Mt of ferrochromium.\nAccording to John F. Papp, writing for the USGS, \"Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium.\"\nThe largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing the rest of about 18% of the world production.\nThe two main products of chromium ore refining are [ferrochromium](https://bliptext.com/articles/ferrochromium) and metallic chromium.\nFor those products the ore smelter process differs considerably.\nFor the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in [electric arc furnace](https://bliptext.com/articles/electric-arc-furnace) or in smaller smelters with either [aluminium](https://bliptext.com/articles/aluminium) or [silicon](https://bliptext.com/articles/silicon) in an [aluminothermic reaction](https://bliptext.com/articles/aluminothermic-reaction).\nFor the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process.\nThe chromite ore is heated with a mixture of [calcium carbonate](https://bliptext.com/articles/calcium-carbonate) and [sodium carbonate](https://bliptext.com/articles/sodium-carbonate) in the presence of air.\nThe chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.\nThe subsequent leaching at higher elevated temperatures dissolves the [chromates](https://bliptext.com/articles/chromates) and leaves the insoluble iron oxide.\nThe chromate is converted by [sulfuric acid](https://bliptext.com/articles/sulfuric-acid) into the dichromate.\nThe dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.\n# [Piece of chromium produced with aluminothermic reaction | upload.wikimedia.org/wikipedia/commons/c/cf/Chrom///1.jpg]\n# [World production trend of chromium | upload.wikimedia.org/wikipedia/commons/5/5f/Chromium///-///world///production///trend.svg]\n# [Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains | upload.wikimedia.org/wikipedia/commons/4/42/Chromium///zone///refined///and///1cm3///cube.jpg]\n# [Chromium ore output in 2002 | upload.wikimedia.org/wikipedia/commons/2/2c/World///Chromium///Production///2002.svg]\n\n# Applications\nThe creation of metal alloys account for 85% of the available chromium's usage.\nThe remainder of chromium is used in the [chemical](https://bliptext.com/articles/chemical-industry), [refractory](https://bliptext.com/articles/refractory), and [foundry](https://bliptext.com/articles/foundry) industries.\n\n## Metallurgy\nThe strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.\n[High-speed tool steels](https://bliptext.com/articles/high-speed-steel) contain 3–5% chromium.\n[Stainless steel](https://bliptext.com/articles/stainless-steel), the primary corrosion-resistant metal alloy, is formed when chromium is introduced to [iron](https://bliptext.com/articles/iron) in concentrations above 11%.\nFor stainless steel's formation, ferrochromium is added to the molten iron.\nAlso, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries.\nFor example, [Inconel](https://bliptext.com/articles/inconel) 718 contains 18.6% chromium.\nBecause of the excellent high-temperature properties of these nickel [superalloys](https://bliptext.com/articles/superalloy), they are used in [jet engines](https://bliptext.com/articles/jet-engine) and [gas turbines](https://bliptext.com/articles/gas-turbine) in lieu of common structural materials.\n[ASTM](https://bliptext.com/articles/astm) B163 relies on chromium for condenser and heat-exchanger tubes, while [castings](https://bliptext.com/articles/castings) with high strength at elevated temperatures that contain chromium are standardised with [ASTM](https://bliptext.com/articles/astm) A567.\n[AISI](https://bliptext.com/articles/american-iron-and-steel-institute) type 332 is used where high temperature would normally cause [carburization](https://bliptext.com/articles/carburization), [oxidation](https://bliptext.com/articles/oxidation) or [corrosion](https://bliptext.com/articles/corrosion).\n[Incoloy](https://bliptext.com/articles/incoloy) 800 \"is capable of remaining stable and maintaining its [austenitic](https://bliptext.com/articles/austenitic) structure even after long time exposures to high temperatures\".\n[Nichrome](https://bliptext.com/articles/nichrome) is used as resistance wire for heating elements in things like [toasters](https://bliptext.com/articles/toasters) and space heaters.\nThese uses make chromium a [strategic material](https://bliptext.com/articles/strategic-material).\nConsequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it \"may become a critical material during the emergency\".\nThe United States likewise considered chromium \"essential for the German war industry\" and made intense diplomatic efforts to keep it out of the hands of [Nazi Germany](https://bliptext.com/articles/nazi-germany).\nThe high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals.\nA layer of chromium is deposited on pretreated metallic surfaces by [electroplating](https://bliptext.com/articles/electroplating) techniques.\nThere are two deposition methods: thin, and thick.\nThin deposition involves a layer of chromium below 1 μm thickness deposited by [chrome plating](https://bliptext.com/articles/chrome-plating), and is used for decorative surfaces.\nThicker chromium layers are deposited if wear-resistant surfaces are needed.\nBoth methods use acidic chromate or [dichromate](https://bliptext.com/articles/dichromate) solutions.\nTo prevent the energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used.\nIn the [chromate conversion coating](https://bliptext.com/articles/chromate-conversion-coating) process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium.\nThis [passivation](https://bliptext.com/articles/passivation-chemistry) and the self-healing properties of the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.\nBecause of environmental and health regulations on chromates, alternative coating methods are under development.\nChromic acid [anodizing](https://bliptext.com/articles/anodizing) (or Type I [anodizing](https://bliptext.com/articles/anodizing)) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses [chromic acid](https://bliptext.com/articles/chromic-acid) as an electrolyte in the solution.\nDuring anodization, an oxide layer is formed on the aluminium.\nThe use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.\nThe high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least a change to less toxic chromium(III) compounds.\n# [Stainless steel cutlery made from Cromargan 18/10, containing 18% chromium | upload.wikimedia.org/wikipedia/commons/6/66/Besteck///WMF///Stockholm///ca///1960er.jpg]\n# [Decorative chrome plating on a motorcycle | upload.wikimedia.org/wikipedia/commons/e/e1/Motorcycle///Reflections///bw///edit.jpg]\n\n## Pigment\nThe mineral [crocoite](https://bliptext.com/articles/crocoite) (which is also [lead chromate](https://bliptext.com/articles/lead-chromate) PbCrO4) was used as a yellow pigment shortly after its discovery.\nAfter a synthesis method became available starting from the more abundant chromite, [chrome yellow](https://bliptext.com/articles/chrome-yellow) was, together with [cadmium yellow](https://bliptext.com/articles/cadmium-yellow), one of the most used yellow pigments.\nThe pigment does not photodegrade, but it tends to darken due to the formation of chromium(III) oxide.\nIt has a strong color, and was used for school buses in the United States and for the postal services (for example, the [Deutsche Post](https://bliptext.com/articles/deutsche-post)) in Europe.\nThe use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium.\nOther pigments that are based around chromium are, for example, the deep shade of red pigment [chrome red](https://bliptext.com/articles/chrome-red), which is simply lead chromate with [lead(II) hydroxide](https://bliptext.com/articles/lead-ii-hydroxide) (PbCrO4·Pb(OH)2).\nA very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate.\nA wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution.\nThis used zinc tetroxychromate dispersed in a solution of [polyvinyl butyral](https://bliptext.com/articles/polyvinyl-butyral).\nAn 8% solution of phosphoric acid in solvent was added just before application.\nIt was found that an easily oxidized alcohol was an essential ingredient.\nA thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured.\nThere is still a question as to the correct mechanism.\nChrome green is a mixture of [Prussian blue](https://bliptext.com/articles/prussian-blue) and [chrome yellow](https://bliptext.com/articles/chrome-yellow), while the chrome oxide green is [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium oxides are also used as a green pigment in the field of glassmaking and also as a glaze for ceramics.\nGreen chromium oxide is extremely [lightfast](https://bliptext.com/articles/lightfastness) and as such is used in cladding coatings.\nIt is also the main ingredient in [infrared](https://bliptext.com/articles/infrared) reflecting paints, used by the armed forces to paint vehicles and to give them the same [infrared](https://bliptext.com/articles/infrared) reflectance as green leaves.\n\n## Other uses\nChromium(III) ions present in [corundum](https://bliptext.com/articles/corundum) crystals (aluminium oxide) cause them to be colored red; when [corundum](https://bliptext.com/articles/corundum) appears as such, it is known as a [ruby](https://bliptext.com/articles/ruby).\nIf the corundum is lacking in chromium(III) ions, it is known as a [sapphire](https://bliptext.com/articles/sapphire).\nA red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies.\nSuch a synthetic ruby crystal was the basis for the first [laser](https://bliptext.com/articles/laser), produced in 1960, which relied on [stimulated emission](https://bliptext.com/articles/stimulated-emission) of light from the chromium atoms in such a crystal.\nRuby has a laser transition at 694.3 nanometers, in a deep red color.\nChromium(VI) salts are used for the preservation of wood.\nFor example, [chromated copper arsenate](https://bliptext.com/articles/chromated-copper-arsenate) (CCA) is used in [timber treatment](https://bliptext.com/articles/timber-treatment) to protect wood from decay fungi, wood-attacking insects, including [termites](https://bliptext.com/articles/termites), and marine borers.\nThe formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%.\nIn the United States, 65,300 metric tons of CCA solution were used in 1996.\nChromium(III) salts, especially [chrome alum](https://bliptext.com/articles/chrome-alum) and [chromium(III) sulfate](https://bliptext.com/articles/chromium-iii-sulfate), are used in the tanning of [leather](https://bliptext.com/articles/leather).\nThe chromium(III) stabilizes the leather by cross linking the [collagen](https://bliptext.com/articles/collagen) fibers.\nChromium tanned leather can contain 4–5% of chromium, which is tightly bound to the proteins.\nAlthough the form of chromium used for tanning is not the toxic hexavalent variety, there remains interest in management of chromium in the tanning industry.\nRecovery and reuse, direct/indirect recycling, and \"chrome-less\" or \"chrome-free\" tanning are practiced to better manage chromium usage.\nThe high heat resistivity and high melting point makes [chromite](https://bliptext.com/articles/chromite) and chromium(III) oxide a material for high temperature refractory applications, like [blast furnaces](https://bliptext.com/articles/blast-furnace), cement [kilns](https://bliptext.com/articles/kiln), molds for the firing of [bricks](https://bliptext.com/articles/brick) and as foundry sands for the [casting](https://bliptext.com/articles/casting-metalworking) of metals.\nIn these applications, the refractory materials are made from mixtures of chromite and magnesite.\nThe use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).\nSeveral chromium compounds are used as [catalysts](https://bliptext.com/articles/catalyst) for processing hydrocarbons.\nFor example, the [Phillips catalyst](https://bliptext.com/articles/phillips-catalyst), prepared from chromium oxides, is used for the production of about half the world's [polyethylene](https://bliptext.com/articles/polyethylene).\nFe-Cr mixed oxides are employed as high-temperature catalysts for the [water gas shift reaction](https://bliptext.com/articles/water-gas-shift-reaction).\n[Copper chromite](https://bliptext.com/articles/copper-chromite) is a useful [hydrogenation](https://bliptext.com/articles/hydrogenation) catalyst.\n# [Red crystal of a ruby laser | upload.wikimedia.org/wikipedia/commons/7/7d/5///Maiman///Laser///Components.jpg]\n\n## Uses of compounds\n\n# Biological role\nThe possible nutritional value of chromium(III) is unproven.\nAlthough chromium is regarded as a trace element and [dietary mineral](https://bliptext.com/articles/mineral-nutrient), its suspected roles in the action of [insulin](https://bliptext.com/articles/insulin) – a hormone that mediates the metabolism and storage of carbohydrate, fat, and protein – have not been adequately established.\nThe [mechanism of its actions](https://bliptext.com/articles/mechanism-of-action) in the body is undefined, leaving in doubt whether chromium has a biological role in healthy people.\nIn contrast, [hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium) (Cr(VI) or Cr6+) is highly toxic and [mutagenic](https://bliptext.com/articles/mutagen).\nIngestion of chromium(VI) in water has been linked to stomach tumors, and it may also cause allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis).\n\"[Chromium deficiency](https://bliptext.com/articles/chromium-deficiency)\", involving a lack of Cr(III) in the body, or perhaps some complex of it, such as [glucose tolerance factor](https://bliptext.com/articles/glucose-tolerance-factor), is not accepted as a medical condition, as it has no symptoms and healthy people do not require chromium supplementation.\nSome studies suggest that the biologically active form of chromium(III) is transported in the body via an oligopeptide called [low-molecular-weight chromium-binding substance](https://bliptext.com/articles/low-molecular-weight-chromium-binding-substance) (chromodulin), which might play a role in the insulin signaling pathway.\nThe chromium content of common foods is generally low (1–13 micrograms per serving).\nThe chromium content of food varies widely, due to differences in soil mineral content, growing season, plant [cultivar](https://bliptext.com/articles/cultivar), and contamination during processing.\nChromium (and [nickel](https://bliptext.com/articles/nickel)) leach into food cooked in stainless steel, with the effect being largest when the cookware is new.\nAcidic foods that are cooked for many hours also exacerbate this effect.\n\n## Dietary recommendations\nThere is disagreement on chromium's status as an essential nutrient.\nGovernmental departments from Australia, New Zealand, India, and Japan consider chromium as essential, while the United States and European Food Safety Authority of the European Union do not.\nThe U.S. [National Academy of Medicine](https://bliptext.com/articles/national-academy-of-medicine) (NAM) updated the [Estimated Average Requirements](https://bliptext.com/articles/dietary-reference-intake) (EARs) and the [Recommended Dietary Allowances](https://bliptext.com/articles/dietary-reference-intake) (RDAs) for chromium in 2001.\nFor chromium, there was insufficient information to set EARs and RDAs, so its needs are described as estimates for [Adequate Intake](https://bliptext.com/articles/dietary-reference-intake) (AI).\nFrom a 2001 assessment, AI of chromium for women ages 14 through 50 is 25 μg/day, and the AI for women ages 50 and above is 20 μg/day.\nThe AIs for women who are pregnant are 30 μg/day, and for women who are lactating, the set AI is 45 μg/day.\nThe AI for men ages 14 through 50 is 35 μg/day, and the AI for men ages 50 and above is 30 μg/day.\nFor children ages 1 through 13, the AI increases with age from 0.2 μg/day up to 25 μg/day.\nAs for safety, the NAM sets [Tolerable Upper Intake Levels](https://bliptext.com/articles/dietary-reference-intake) (ULs) for vitamins and minerals when the evidence is sufficient.\nIn the case of chromium, there is not yet enough information, hence no UL has been established.\nCollectively, the EARs, RDAs, AIs, and ULs are the parameters for the nutrition recommendation system known as [Dietary Reference Intake](https://bliptext.com/articles/dietary-reference-intake) (DRI).\nAustralia and New Zealand consider chromium to be an essential nutrient, with an AI of 35 μg/day for men, 25 μg/day for women, 30 μg/day for women who are pregnant, and 45 μg/day for women who are lactating.\nA UL has not been set due to the lack of sufficient data.\nIndia considers chromium to be an essential nutrient, with an adult recommended intake of 33 μg/day.\nJapan also considers chromium to be an essential nutrient, with an AI of 10 μg/day for adults, including women who are pregnant or lactating.\nA UL has not been set.\nThe EFSA does not consider chromium to be an essential nutrient.\n\n### Labeling\nFor U.S. food and dietary supplement labeling purposes, the amount of the substance in a serving is expressed as a percent of the [Daily Value](https://bliptext.com/articles/reference-daily-intake) (%DV).\nFor chromium labeling purposes, 100% of the Daily Value was 120 μg. As of 27 May 2016, the percentage of daily value was revised to 35 μg to bring the chromium intake into a consensus with the official [Recommended Dietary Allowance](https://bliptext.com/articles/dietary-reference-intake).\nA table of the old and new adult daily values in the United States is provided at [Reference Daily Intake](https://bliptext.com/articles/reference-daily-intake).\nAfter evaluation of research on the potential nutritional value of chromium, the European Food Safety Authority concluded that there was no evidence of benefit by dietary chromium in healthy people, thereby declining to establish recommendations in Europe for dietary intake of chromium.\n\n## Food sources\nFood composition databases such as those maintained by the U.S. Department of Agriculture do not contain information on the chromium content of foods.\nA wide variety of animal and vegetable foods contain chromium.\nContent per serving is influenced by the chromium content of the soil in which the plants are grown, by foodstuffs fed to animals, and by processing methods, as chromium is leached into foods if processed or cooked in stainless steel equipment.\nOne diet analysis study conducted in Mexico reported an average daily chromium intake of 30 micrograms.\nAn estimated 31% of adults in the United States consume multi-vitamin/mineral dietary supplements, which often contain 25 to 60 micrograms of chromium.\n\n## Supplementation\nChromium is an ingredient in [total parenteral nutrition](https://bliptext.com/articles/total-parenteral-nutrition) (TPN), because deficiency can occur after months of intravenous feeding with chromium-free TPN.\nIt is also added to nutritional products for [preterm infants](https://bliptext.com/articles/preterm-infant).\nAlthough the mechanism of action in biological roles for chromium is unclear, in the United States chromium-containing products are sold as non-prescription dietary supplements in amounts ranging from 50 to 1,000 μg. Lower amounts of chromium are also often incorporated into multi-vitamin/mineral supplements consumed by an estimated 31% of adults in the United States.\nChemical compounds used in dietary supplements include chromium chloride, chromium citrate, [chromium(III) picolinate](https://bliptext.com/articles/chromium-iii-picolinate), [chromium(III) polynicotinate](https://bliptext.com/articles/chromium-polynicotinate), and other chemical compositions.\nThe benefit of supplements has not been proven.\n\n### Initiation of research on glucose\nThe notion of chromium as a potential regulator of glucose metabolism began in the 1950s when scientists performed a series of experiments controlling the diet of rats.\nThe experimenters subjected the rats to a chromium deficient diet, and witnessed an inability to respond effectively to increased levels of blood glucose.\nA chromium-rich [Brewer's yeast](https://bliptext.com/articles/yeast) was provided in the diet, enabling the rats to effectively metabolize glucose, and so giving evidence that chromium may have a role in glucose management.\n\n## Approved and disapproved health claims\nIn 2005, the U.S. Food and Drug Administration had approved a qualified health claim for chromium picolinate with a requirement for specific label wording:\nIn other parts of the petition, the FDA rejected claims for chromium picolinate and cardiovascular disease, retinopathy or kidney disease caused by abnormally high blood sugar levels.\nAs of March 2024, this ruling on chromium remains in effect.\nIn 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements.\nApproved labeling statements include: a factor in the maintenance of good health, provides support for healthy glucose metabolism, helps the body to metabolize carbohydrates and helps the body to metabolize fats.\nThe European Food Safety Authority approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration, but rejected claims for maintenance or achievement of a normal body weight, or reduction of tiredness or fatigue.\nHowever, in a 2014 reassessment of studies to determine whether a Dietary Reference Intake value could be established for chromium, EFSA stated:\n\n### Diabetes\nGiven the evidence for chromium deficiency causing problems with glucose management in the context of intravenous nutrition products formulated without chromium, research interest turned to whether chromium supplementation would benefit people who have type 2 diabetes but are not chromium deficient.\nLooking at the results from four meta-analyses, one reported a statistically significant decrease in fasting [plasma glucose](https://bliptext.com/articles/plasma-glucose) levels and a non-significant trend in lower [hemoglobin A1C](https://bliptext.com/articles/glycated-hemoglobin).\nA second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either.\nA review published in 2016 listed 53 [randomized clinical trials](https://bliptext.com/articles/randomized-clinical-trial) that were included in one or more of six [meta-analyses](https://bliptext.com/articles/meta-analysis).\nIt concluded that whereas there may be modest decreases in fasting blood glucose and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome.\n\n### Body weight\nTwo [systematic reviews](https://bliptext.com/articles/systematic-review) looked at chromium supplements as a mean of managing body weight in overweight and obese people.\nOne, limited to [chromium picolinate](https://bliptext.com/articles/chromium-picolinate), a common supplement ingredient, reported a statistically significant −1.1 kg (2.4 lb) weight loss in trials longer than 12 weeks.\nThe other included all chromium compounds and reported a statistically significant −0.50 kg (1.1 lb) weight change.\nChange in percent body fat did not reach statistical significance.\nAuthors of both reviews considered the clinical relevance of this modest weight loss as uncertain/unreliable.\nThe European Food Safety Authority reviewed the literature and concluded that there was insufficient evidence to support a claim.\n\n### Sports\nChromium is promoted as a sports performance dietary supplement, based on the theory that it potentiates insulin activity, with anticipated results of increased muscle mass, and faster recovery of glycogen storage during post-exercise recovery.\nA review of clinical trials reported that chromium supplementation did not improve exercise performance or increase muscle strength.\nThe International Olympic Committee reviewed dietary supplements for high-performance athletes in 2018 and concluded there was no need to increase chromium intake for athletes, nor support for claims of losing body fat.\n\n## Fresh-water fish\nIrrigation water standards for chromium are 0.1 mg/L, but some rivers in [Bangladesh](https://bliptext.com/articles/bangladesh) are more than five times that amount.\nThe standard for fish for human consumption is less than 1 mg/kg, but many tested samples were more than five times that amount.\nChromium, especially hexavalent chromium, is highly toxic to fish because it is easily absorbed across the gills, readily enters blood circulation, crosses cell membranes and bioconcentrates up the food chain.\nIn contrast, the toxicity of trivalent chromium is very low, attributed to poor membrane permeability and little biomagnification.\nAcute and chronic exposure to chromium(VI) affects fish behavior, physiology, reproduction and survival.\nHyperactivity and erratic swimming have been reported in contaminated environments.\nEgg hatching and fingerling survival are affected.\nIn adult fish there are reports of histopathological damage to liver, kidney, muscle, intestines, and gills.\nMechanisms include mutagenic gene damage and disruptions of enzyme functions.\nThere is evidence that fish may not require chromium, but benefit from a measured amount in diet.\nIn one study, juvenile fish gained weight on a zero chromium diet, but the addition of 500 μg of chromium in the form of chromium chloride or other supplement types, per kilogram of food (dry weight), increased weight gain.\nAt 2,000 μg/kg the weight gain was no better than with the zero chromium diet, and there were increased DNA strand breaks.\n\n# Precautions\nWater-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.\nBecause of the specific [transport](https://bliptext.com/articles/transport-protein) mechanisms, only limited amounts of chromium(III) enter the cells.\nAcute oral toxicity ranges between 50 and 150 mg/kg.\nA 2008 review suggested that moderate uptake of chromium(III) through dietary supplements poses no genetic-toxic risk.\nIn the US, the [Occupational Safety and Health Administration](https://bliptext.com/articles/occupational-safety-and-health-administration) (OSHA) has designated an air [permissible exposure limit](https://bliptext.com/articles/permissible-exposure-limit) (PEL) in the workplace as a time-weighted average (TWA) of 1 mg/m3.\nThe [National Institute for Occupational Safety and Health](https://bliptext.com/articles/national-institute-for-occupational-safety-and-health) (NIOSH) has set a [recommended exposure limit](https://bliptext.com/articles/recommended-exposure-limit) (REL) of 0.5 mg/m3, time-weighted average.\nThe [IDLH](https://bliptext.com/articles/idlh) (immediately dangerous to life and health) value is 250 mg/m3.\n\n## Chromium(VI) toxicity\nThe acute [oral](https://bliptext.com/articles/mouth) [toxicity](https://bliptext.com/articles/toxicity) for [chromium(VI)](https://bliptext.com/articles/hexavalent-chromium) ranges between 1.5 and 3.3 mg/kg.\nIn the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells.\nThe chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also [sulfate](https://bliptext.com/articles/sulfate) and [phosphate](https://bliptext.com/articles/phosphate) ions enter the cell.\nThe acute toxicity of chromium(VI) is due to its strong [oxidant](https://bliptext.com/articles/redox) properties.\nAfter it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions.\n[Hemolysis](https://bliptext.com/articles/hemolysis), [renal](https://bliptext.com/articles/renal), and liver failure result.\nAggressive dialysis can be therapeutic.\nThe [carcinogenity](https://bliptext.com/articles/carcinogenity) of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.\nThree mechanisms have been proposed to describe the [genotoxicity](https://bliptext.com/articles/genotoxicity) of chromium(VI).\nThe first mechanism includes highly reactive [hydroxyl radicals](https://bliptext.com/articles/hydroxyl-radical) and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III).\nThe second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the [DNA](https://bliptext.com/articles/dna).\nThe last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.\nChromium salts (chromates) are also the cause of [allergic reactions](https://bliptext.com/articles/allergic-reaction) in some people.\nChromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.\nContact with products containing chromates can lead to allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis) and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as \"chrome ulcers\".\nThis condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.\n\n## Environmental issues\nBecause chromium compounds were used in [dyes](https://bliptext.com/articles/dye), [paints](https://bliptext.com/articles/paint), and [leather](https://bliptext.com/articles/leather) [tanning](https://bliptext.com/articles/tanning-leather) compounds, these compounds are often found in soil and [groundwater](https://bliptext.com/articles/groundwater) at active and abandoned industrial sites, needing [environmental cleanup](https://bliptext.com/articles/environmental-cleanup) and [remediation](https://bliptext.com/articles/environmental-remediation).\n[Primer paint](https://bliptext.com/articles/primer-paint) containing hexavalent chromium is still widely used for [aerospace](https://bliptext.com/articles/aerospace) and [automobile](https://bliptext.com/articles/automobile) refinishing applications.\nIn 2010, the [Environmental Working Group](https://bliptext.com/articles/environmental-working-group) studied the drinking water in 35 American cities in the first nationwide study.\nThe study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with [Norman, Oklahoma](https://bliptext.com/articles/norman-oklahoma), at the top of list; 25 cities had levels that exceeded California's proposed limit.\nThe more toxic hexavalent chromium form can be reduced to the less soluble trivalent oxidation state in soils by organic matter, ferrous iron, sulfides, and other reducing agents, with the rates of such reduction being faster under more acidic conditions than under more alkaline ones.\nIn contrast, trivalent chromium can be oxidized to hexavalent chromium in soils by manganese oxides, such as Mn(III) and Mn(IV) compounds.\nSince the solubility and toxicity of chromium (VI) are greater that those of chromium (III), the oxidation-reduction conversions between the two oxidation states have implications for movement and bioavailability of chromium in soils, groundwater, and plants.\n\n# General bibliography","wordIndex":786,"createdAt":"2025-03-18T15:16:43.855Z","user":{"id":"jr9320kzLD37CkxadNfMG9YBINNdhTeS","name":"The Raters","image":"https://lh3.googleusercontent.com/a/ACg8ocIdQIQQjHI233tCJ_h-vtFv9t351nMGaL3Sfolwv8P7mLg2Ez0=s96-c"}},{"id":"0b1e4693-ee71-4715-a1bd-0de75329801f","wordChanged":"[antiferromagnetism](https://bliptext.com/articles/antiferromagnetism)","newWord":":::summary\n**Vickers Hardness:** 950HV \n**Vickers Hardness Ref:** https://www.journalmt.com/pdfs/mft/2018/04/16.pdf \n:::\n\n# \n**Chromium** is a [chemical element](https://bliptext.com/articles/chemical-element); it has [symbol](https://bliptext.com/articles/symbol-chemistry) **Cr** and [atomic number](https://bliptext.com/articles/atomic-number) 24.\nIt is the first element in [group 6](https://bliptext.com/articles/group-6-element).\nIt is a steely-grey, [lustrous](https://bliptext.com/articles/luster-mineralogy), hard, and brittle [transition metal](https://bliptext.com/articles/transition-metal).\nChromium is valued for its high [corrosion](https://bliptext.com/articles/corrosion) resistance and [hardness](https://bliptext.com/articles/hardness).\nA major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form [stainless steel](https://bliptext.com/articles/stainless-steel).\nStainless steel and [chrome plating](https://bliptext.com/articles/chrome-plating) ([electroplating](https://bliptext.com/articles/electroplating) with chromium) together comprise 85% of the commercial use.\nChromium is also greatly valued as a [metal](https://bliptext.com/articles/metal) that is able to be highly [polished](https://bliptext.com/articles/polishing) while resisting [tarnishing](https://bliptext.com/articles/tarnish).\nPolished chromium reflects almost 70% of the [visible spectrum](https://bliptext.com/articles/visible-spectrum), and almost 90% of [infrared light](https://bliptext.com/articles/infrared).\nThe name of the element is derived from the [Greek](https://bliptext.com/articles/ancient-greek) word χρῶμα, chrōma, meaning [color](https://bliptext.com/articles/color), because many chromium compounds are intensely [color](https://bliptext.com/articles/color)ed.\nIndustrial production of chromium proceeds from [chromite](https://bliptext.com/articles/chromite) ore (mostly FeCr2O4) to produce [ferrochromium](https://bliptext.com/articles/ferrochromium), an iron-chromium alloy, by means of [aluminothermic](https://bliptext.com/articles/aluminothermic-reaction) or [silicothermic reactions](https://bliptext.com/articles/silicothermic-reaction).\nFerrochromium is then used to produce alloys such as stainless steel.\nPure chromium metal is produced by a different process: [roasting](https://bliptext.com/articles/roasting-metallurgy) and [leaching](https://bliptext.com/articles/leaching-metallurgy) of chromite to separate it from iron, followed by reduction with [carbon](https://bliptext.com/articles/carbon) and then [aluminium](https://bliptext.com/articles/aluminium).\n[Trivalent](https://bliptext.com/articles/trivalent) chromium (Cr(III)) occurs naturally in many foods and is sold as a [dietary supplement](https://bliptext.com/articles/dietary-supplement), although there is insufficient evidence that dietary chromium provides nutritional benefit to people.\nIn 2014, the [European Food Safety Authority](https://bliptext.com/articles/european-food-safety-authority) concluded that research on dietary chromium did not justify it to be recognized as an essential [nutrient](https://bliptext.com/articles/nutrient).\nWhile chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called \"[hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium)\", is toxic and [carcinogenic](https://bliptext.com/articles/carcinogenic).\nAccording to the European Chemicals Agency (ECHA), [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) that is used in industrial electroplating processes is a \"substance of very high concern\" (SVHC).\n\n# Physical properties\n\n## Atomic\nGaseous chromium has a ground-state [electron configuration](https://bliptext.com/articles/electron-configuration) of [ [Ar](https://bliptext.com/articles/argon)] 3d5 4s1.\nIt is the first element in the periodic table whose configuration violates the [Aufbau principle](https://bliptext.com/articles/aufbau-principle).\nExceptions to the principle also occur later in the periodic table for elements such as [copper](https://bliptext.com/articles/copper), [niobium](https://bliptext.com/articles/niobium) and [molybdenum](https://bliptext.com/articles/molybdenum).\nChromium is the first element in the 3d series where the 3d electrons start to sink into the core; they thus contribute less to [metallic bonding](https://bliptext.com/articles/metallic-bonding), and hence the melting and boiling points and the [enthalpy of atomisation](https://bliptext.com/articles/enthalpy-of-atomisation) of chromium are lower than those of the preceding element [vanadium](https://bliptext.com/articles/vanadium).\nChromium(VI) is a strong [oxidising agent](https://bliptext.com/articles/oxidising-agent) in contrast to the [molybdenum](https://bliptext.com/articles/molybdenum)(VI) and [tungsten](https://bliptext.com/articles/tungsten)(VI) oxides.\n\n## Bulk\nChromium is the third hardest element after [carbon](https://bliptext.com/articles/carbon) ([diamond](https://bliptext.com/articles/diamond)) and [boron](https://bliptext.com/articles/boron).\nIts [Mohs hardness](https://bliptext.com/articles/mohs-scale-of-mineral-hardness) is 8.5, which means that it can scratch samples of [quartz](https://bliptext.com/articles/quartz) and [topaz](https://bliptext.com/articles/topaz), but can be scratched by [corundum](https://bliptext.com/articles/corundum).\nChromium is highly resistant to [tarnishing](https://bliptext.com/articles/tarnish), which makes it useful as a metal that preserves its outermost layer from [corroding](https://bliptext.com/articles/corrosion), unlike other metals such as [copper](https://bliptext.com/articles/copper), [magnesium](https://bliptext.com/articles/magnesium), and [aluminium](https://bliptext.com/articles/aluminium).\nChromium has a [melting point](https://bliptext.com/articles/melting-point) of 1907 °C (3465 °F), which is relatively low compared to the majority of transition metals.\nHowever, it still has the second highest melting point out of all the [period 4 elements](https://bliptext.com/articles/period-4-element), being topped by [vanadium](https://bliptext.com/articles/vanadium) by 3 °C (5 °F) at 1910 °C (3470 °F).\nThe [boiling point](https://bliptext.com/articles/boiling-point) of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest [boiling point](https://bliptext.com/articles/boiling-point) out of the [Period 4](https://bliptext.com/articles/period-4) [transition metals](https://bliptext.com/articles/transition-metal) alone behind [copper](https://bliptext.com/articles/copper), [manganese](https://bliptext.com/articles/manganese) and [zinc](https://bliptext.com/articles/zinc).\nThe [electrical resistivity](https://bliptext.com/articles/electrical-resistivity-and-conductivity) of chromium at 20 °C is 125 [nanoohm](https://bliptext.com/articles/ohm)-[meters](https://bliptext.com/articles/meter).\nChromium has a high [specular reflection](https://bliptext.com/articles/specular-reflection) in comparison to other transition metals.\nIn [infrared](https://bliptext.com/articles/infrared), at 425 [μm](https://bliptext.com/articles/micrometre), chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 [μm](https://bliptext.com/articles/micrometre) before rising again to 90% at 4000 [μm](https://bliptext.com/articles/micrometre).\nWhen chromium is used in [stainless steel](https://bliptext.com/articles/stainless-steel) alloys and [polished](https://bliptext.com/articles/polishing), the specular reflection decreases with the inclusion of additional metals, yet is still high in comparison with other alloys.\nBetween 40% and 60% of the visible spectrum is reflected from polished stainless steel.\nThe explanation on why chromium displays such a high turnout of reflected [photon](https://bliptext.com/articles/photon) waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties.\nChromium has unique magnetic properties; it is the only elemental solid that shows [antiferromagnetic](https://bliptext.com/articles/antiferromagnetic) ordering at room temperature and below.\nAbove 38 °C, its magnetic ordering becomes [paramagnetic](https://bliptext.com/articles/paramagnetic).\nThe antiferromagnetic properties, which cause the chromium atoms to temporarily [ionize](https://bliptext.com/articles/ionization) and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the [lattice periodicity](https://bliptext.com/articles/crystal-structure).\nThis is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers.\nFrom here, the frequency-dependent [relative permittivity](https://bliptext.com/articles/relative-permittivity) of chromium, deriving from [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations) and Chromakopia By, leaves chromium with a high infrared and visible light reflectance.\n# [Sample of chromium metal | upload.wikimedia.org/wikipedia/commons/a/a1/Chromium.jpg]\n\n### Passivation\nChromium metal in air is [passivated](https://bliptext.com/articles/passivation-chemistry): it forms a thin, protective surface layer of chromium oxide with the [corundum](https://bliptext.com/articles/corundum-structure) structure.\nPassivation can be enhanced by short contact with [oxidizing acids](https://bliptext.com/articles/oxidizing-acid) like [nitric acid](https://bliptext.com/articles/nitric-acid).\nPassivated chromium is stable against acids.\nPassivation can be removed with a strong [reducing agent](https://bliptext.com/articles/reducing-agent) that destroys the protective oxide layer on the metal.\nChromium metal treated in this way readily dissolves in weak acids.\nThe surface [chromia](https://bliptext.com/articles/chromium-iii-oxide) Cr2O3 scale, is adherent to the metal.\nIn contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued [rusting](https://bliptext.com/articles/rust).\nAt room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward [diffusion](https://bliptext.com/articles/atomic-diffusion) of metal ions across the scale.\nAbove 950 °C volatile [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) CrO3 forms from the chromia scale, limiting the scale thickness and oxidation protection.\nChromium, unlike iron and nickel, does not suffer from [hydrogen embrittlement](https://bliptext.com/articles/hydrogen-embrittlement).\nHowever, it does suffer from nitrogen [embrittlement](https://bliptext.com/articles/embrittlement), reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.\n\n## Isotopes\nNaturally occurring chromium is composed of four stable [isotopes](https://bliptext.com/articles/isotope); 50Cr, 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% [natural abundance](https://bliptext.com/articles/natural-abundance)).\n50Cr is [observationally stable](https://bliptext.com/articles/stable-nuclide), as it is theoretically capable of [decaying](https://bliptext.com/articles/radioactive-decay) to [50Ti](https://bliptext.com/articles/isotopes-of-titanium) via [double electron capture](https://bliptext.com/articles/double-electron-capture) with a [half-life](https://bliptext.com/articles/half-life) of no less than 1.3 years.\nTwenty-five [radioisotopes](https://bliptext.com/articles/radioisotope) have been characterized, ranging from 42Cr to 70Cr; the most stable radioisotope is 51Cr with a half-life of 27.7 days.\nAll of the remaining [radioactive](https://bliptext.com/articles/radioactive) isotopes have half-lives that are less than 24 hours and the majority less than 1 minute.\nChromium also has two [metastable](https://bliptext.com/articles/metastable) [nuclear isomers](https://bliptext.com/articles/nuclear-isomer).\nThe primary [decay mode](https://bliptext.com/articles/decay-mode) before the most abundant stable isotope, 52Cr, is [electron capture](https://bliptext.com/articles/electron-capture) and the primary mode after is [beta decay](https://bliptext.com/articles/beta-decay).\n53Cr is the [radiogenic](https://bliptext.com/articles/radiogenic) decay product of 53[Mn](https://bliptext.com/articles/manganese) (half-life 3.74 million years).\nChromium isotopes are typically collocated (and compounded) with [manganese](https://bliptext.com/articles/manganese) isotopes.\nThis circumstance is useful in [isotope geology](https://bliptext.com/articles/isotope-geology).\nManganese-chromium isotope ratios reinforce the evidence from [26Al](https://bliptext.com/articles/aluminium-26) and 107[Pd](https://bliptext.com/articles/palladium) concerning the early history of the [Solar System](https://bliptext.com/articles/solar-system).\nVariations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies.\nHence 53Cr provides additional evidence for [nucleosynthetic](https://bliptext.com/articles/nucleosynthesis) processes immediately before coalescence of the Solar System.\n53Cr has been posited as a proxy for atmospheric oxygen concentration.\n\n# Chemistry and compounds\nChromium is a member of [group 6](https://bliptext.com/articles/group-6-element), of the [transition metals](https://bliptext.com/articles/transition-metal).\nThe +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.\n# [The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide | upload.wikimedia.org/wikipedia/commons/c/c3/Chromium///in///water///pourbiax///diagram.png]\n\n## Common oxidation states\n\n### Chromium(0)\nMany Cr(0) complexes are known.\n[Bis(benzene)chromium](https://bliptext.com/articles/bis-benzene-chromium) and [chromium hexacarbonyl](https://bliptext.com/articles/chromium-hexacarbonyl) are highlights in [organochromium chemistry](https://bliptext.com/articles/organochromium-chemistry).\n\n### Chromium(II)\nChromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air.\nWater-stable [chromium(II) chloride](https://bliptext.com/articles/chromium-ii-chloride) that can be made by reducing chromium(III) chloride with zinc.\nThe resulting bright blue solution created from dissolving chromium(II) chloride is stable at neutral [pH](https://bliptext.com/articles/ph).\nSome other notable chromium(II) compounds include [chromium(II) oxide](https://bliptext.com/articles/chromium-ii-oxide), and [chromium(II) sulfate](https://bliptext.com/articles/chromium-ii-sulfate).\nMany chromium(II) carboxylates are known.\nThe red [chromium(II) acetate](https://bliptext.com/articles/chromium-ii-acetate) (Cr2(O2CCH3)4) is somewhat famous.\nIt features a Cr-Cr [quadruple bond](https://bliptext.com/articles/quadruple-bond).\n# [Chromium(II) carbide (Cr3C2) | upload.wikimedia.org/wikipedia/commons/e/eb/Chromium///carbide///Cr3C2.JPG]\n\n### Chromium(III)\nA large number of chromium(III) compounds are known, such as [chromium(III) nitrate](https://bliptext.com/articles/chromium-nitrate), [chromium(III) acetate](https://bliptext.com/articles/chromium-iii-acetate), and [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium(III) can be obtained by dissolving elemental chromium in acids like [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid) or [sulfuric acid](https://bliptext.com/articles/sulfuric-acid), but it can also be formed through the reduction of chromium(VI) by [cytochrome](https://bliptext.com/articles/cytochrome) [c7](https://bliptext.com/articles/cytochrome-c).\nThe ion has a similar radius (63 [pm](https://bliptext.com/articles/picometer)) to (radius 50 [pm](https://bliptext.com/articles/picometer)), and they can replace each other in some compounds, such as in [chrome [alum](https://bliptext.com/articles/alum)](https://bliptext.com/articles/chrome-[alum](https://bliptext.com/articles/alum)) and [alum](https://bliptext.com/articles/alum).\nChromium(III) tends to form [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) complexes.\nCommercially available [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) hydrate is the dark green complex [CrCl2(H2O)4]Cl.\nClosely related compounds are the pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.\nIf anhydrous violet [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) is dissolved in water, the violet solution turns green after some time as the chloride in the inner [coordination sphere](https://bliptext.com/articles/coordination-sphere) is replaced by water.\nThis kind of reaction is also observed with solutions of [chrome alum](https://bliptext.com/articles/chrome-alum) and other water-soluble chromium(III) salts.\nA [tetrahedral](https://bliptext.com/articles/tetrahedral-molecular-geometry) coordination of [chromium(III)](https://bliptext.com/articles/chromium-iii) has been reported for the Cr-centered [Keggin](https://bliptext.com/articles/keggin-structure) anion [α-CrW12O40]5–.\n[Chromium(III) hydroxide](https://bliptext.com/articles/chromium-iii-hydroxide) (Cr(OH)3) is [amphoteric](https://bliptext.com/articles/amphoterism), dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form.\nIt is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), a stable oxide with a crystal structure identical to that of [corundum](https://bliptext.com/articles/corundum).\n# [Anhydrous chromium(III) chloride (CrCl3) | upload.wikimedia.org/wikipedia/commons/3/3b/Chromium%28III%29-chloride-purple-anhydrous-sunlight.jpg]\n\n### Chromium(VI)\n[Chromium(VI) compounds](https://bliptext.com/articles/hexavalent-chromium) are oxidants at low or neutral pH.\n[Chromate](https://bliptext.com/articles/chromate-and-[dichromate](https://bliptext.com/articles/chromate-and-dichromate)) anions and [dichromate](https://bliptext.com/articles/chromate-and-dichromate) (Cr2O72−) anions are the principal ions at this oxidation state.\nThey exist at an equilibrium, determined by pH:\nChromium(VI) oxyhalides are known also and include [chromyl fluoride](https://bliptext.com/articles/chromyl-fluoride) (CrO2F2) and [chromyl chloride](https://bliptext.com/articles/chromyl-chloride).\nHowever, despite several erroneous claims, [chromium hexafluoride](https://bliptext.com/articles/chromium-hexafluoride) (as well as all higher hexahalides) remains unknown, as of 2020.\n[Sodium chromate](https://bliptext.com/articles/sodium-chromate) is produced industrially by the oxidative roasting of [chromite](https://bliptext.com/articles/chromite) ore with [sodium carbonate](https://bliptext.com/articles/sodium-carbonate).\nThe change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of [potassium chromate](https://bliptext.com/articles/potassium-chromate).\nAt yet lower pH values, further condensation to more complex [oxyanions](https://bliptext.com/articles/oxyanion) of chromium is possible.\nBoth the [chromate and dichromate](https://bliptext.com/articles/chromate-and-dichromate) anions are strong oxidizing reagents at low pH:\nThey are, however, only moderately oxidizing at high pH:\nChromium(VI) compounds in solution can be detected by adding an acidic [hydrogen peroxide](https://bliptext.com/articles/hydrogen-peroxide) solution.\nThe unstable dark blue [chromium(VI) peroxide](https://bliptext.com/articles/chromium-vi-peroxide) (CrO5) is formed, which can be stabilized as an ether adduct.\n[Chromic acid](https://bliptext.com/articles/chromic-acid) has the hypothetical formula.\nIt is a vaguely described chemical, despite many well-defined chromates and dichromates being known.\nThe dark red [chromium(VI) oxide](https://bliptext.com/articles/chromium-vi-oxide), the acid [anhydride](https://bliptext.com/articles/anhydride) of chromic acid, is sold industrially as \"chromic acid\".\nIt can be produced by mixing sulfuric acid with dichromate and is a strong oxidizing agent.\n# [Chromium(VI) oxide | upload.wikimedia.org/wikipedia/commons/1/1e/Chrom%28VI%29-oxid.jpg]\n# [Sodium chromate (Na2CrO4) | upload.wikimedia.org/wikipedia/commons/5/51/Chroman///sodn%C3%BD.JPG]\n\n## Other oxidation states\nCompounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate.\nThe only binary compound is the volatile [chromium(V) fluoride](https://bliptext.com/articles/chromium-v-fluoride) (CrF5).\nThis red solid has a melting point of 30 °C and a boiling point of 117 °C.\nIt can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure.\nThe peroxochromate(V) is another example of the +5 oxidation state.\n[Potassium peroxochromate](https://bliptext.com/articles/potassium-tetraperoxochromate-v) (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures.\nThis red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.\nCompounds of chromium(IV) are slightly more common than those of chromium(V).\nThe tetrahalides, [CrF4](https://bliptext.com/articles/chromium-iv-fluoride), [CrCl4](https://bliptext.com/articles/chromium-iv-chloride), and CrBr4, can be produced by treating the trihalides with the corresponding halogen at elevated temperatures.\nSuch compounds are susceptible to disproportionation reactions and are not stable in water.\nOrganic compounds containing Cr(IV) state such as chromium tetra t-butoxide are also known.\nMost chromium(I) compounds are obtained solely by oxidation of electron-rich, [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) chromium(0) complexes.\nOther chromium(I) complexes contain [cyclopentadienyl](https://bliptext.com/articles/cyclopentadienyl) ligands.\nAs verified by [X-ray diffraction](https://bliptext.com/articles/x-ray-diffraction), a Cr-Cr [quintuple bond](https://bliptext.com/articles/quintuple-bond) (length 183.51(4) pm) has also been described.\nExtremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.\n# [Chromium compound determined experimentally to contain a Cr-Cr quintuple bond | upload.wikimedia.org/wikipedia/commons/6/60/5-fold///chromium.png]\n\n# Occurrence\nChromium is the 21st most [abundant element in Earth's crust](https://bliptext.com/articles/abundance-of-elements-in-earth-s-crust) with an average concentration of 100 ppm.\nChromium compounds are found in the environment from the [erosion](https://bliptext.com/articles/erosion) of chromium-containing rocks, and can be redistributed by volcanic eruptions.\nTypical background concentrations of chromium in environmental media are: atmosphere <10 ng/m3; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg.\nChromium is mined as chromite (FeCr2O4) ore.\nAbout two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers.\nUntapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.\nAlthough rare, deposits of [native](https://bliptext.com/articles/native-metal) chromium exist.\nThe [Udachnaya Pipe](https://bliptext.com/articles/udachnaya-pipe) in Russia produces samples of the native metal.\nThis mine is a [kimberlite](https://bliptext.com/articles/kimberlite) pipe, rich in [diamonds](https://bliptext.com/articles/diamond), and the [reducing environment](https://bliptext.com/articles/redox) helped produce both elemental chromium and [diamonds](https://bliptext.com/articles/diamond).\nThe relation between Cr(III) and Cr(VI) strongly depends on [pH](https://bliptext.com/articles/ph) and [oxidative](https://bliptext.com/articles/oxidative) properties of the location.\nIn most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L is Cr(VI).\n# [Crocoite (PbCrO4) | upload.wikimedia.org/wikipedia/commons/a/ac/Crocoite///from///Tasmania.jpg]\n# [Chromite ore | upload.wikimedia.org/wikipedia/commons/0/00/Chromit///1.jpg]\n\n# History\n\n## Early applications\nChromium minerals as pigments came to the attention of the west in the eighteenth century.\nOn 26 July 1761, [Johann Gottlob Lehmann](https://bliptext.com/articles/johann-gottlob-lehmann-scientist) found an orange-red mineral in the [Beryozovskoye mines](https://bliptext.com/articles/beryozovskoye-deposit) in the [Ural Mountains](https://bliptext.com/articles/ural-mountains) which he named Siberian red lead.\nThough misidentified as a [lead](https://bliptext.com/articles/lead) compound with [selenium](https://bliptext.com/articles/selenium) and [iron](https://bliptext.com/articles/iron) components, the mineral was in fact [crocoite](https://bliptext.com/articles/crocoite) with a formula of PbCrO4.\nIn 1770, [Peter Simon Pallas](https://bliptext.com/articles/peter-simon-pallas) visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a [pigment](https://bliptext.com/articles/pigment) in [paints](https://bliptext.com/articles/paint).\nAfter Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region.\nCrocoite would be the principal source of chromium in pigments until the discovery of [chromite](https://bliptext.com/articles/chromite) many years later.\nIn 1794, [Louis Nicolas Vauquelin](https://bliptext.com/articles/louis-nicolas-vauquelin) received samples of crocoite [ore](https://bliptext.com/articles/ore).\nHe produced [chromium trioxide](https://bliptext.com/articles/chromium-vi-oxide) (CrO3) by mixing crocoite with [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid).\nIn 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.\nVauquelin was also able to detect traces of chromium in precious [gemstones](https://bliptext.com/articles/gemstone), such as [ruby](https://bliptext.com/articles/ruby) and [emerald](https://bliptext.com/articles/emerald).\nDuring the nineteenth century, chromium was primarily used not only as a component of paints, but in [tanning](https://bliptext.com/articles/tanning-leather) salts as well.\nFor quite some time, the crocoite found in Russia was the main source for such tanning materials.\nIn 1827, a larger chromite deposit was discovered near [Baltimore](https://bliptext.com/articles/baltimore), United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.\nThis made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of [Bursa](https://bliptext.com/articles/bursa), Turkey.\nWith the development of metallurgy and chemical industries in the Western world, the need for chromium increased.\nChromium is also famous for its reflective, metallic luster when polished.\nIt is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by [electroplating](https://bliptext.com/articles/electroplating).\nChromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.\n# [The red color of rubies is due to trace amounts of chromium within the corundum. | upload.wikimedia.org/wikipedia/commons/c/c4/Cut///Ruby.jpg]\n\n# Production\nApproximately 28.8 million metric tons (Mt) of marketable chromite ore was produced in 2013, and converted into 7.5 Mt of ferrochromium.\nAccording to John F. Papp, writing for the USGS, \"Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium.\"\nThe largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing the rest of about 18% of the world production.\nThe two main products of chromium ore refining are [ferrochromium](https://bliptext.com/articles/ferrochromium) and metallic chromium.\nFor those products the ore smelter process differs considerably.\nFor the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in [electric arc furnace](https://bliptext.com/articles/electric-arc-furnace) or in smaller smelters with either [aluminium](https://bliptext.com/articles/aluminium) or [silicon](https://bliptext.com/articles/silicon) in an [aluminothermic reaction](https://bliptext.com/articles/aluminothermic-reaction).\nFor the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process.\nThe chromite ore is heated with a mixture of [calcium carbonate](https://bliptext.com/articles/calcium-carbonate) and [sodium carbonate](https://bliptext.com/articles/sodium-carbonate) in the presence of air.\nThe chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.\nThe subsequent leaching at higher elevated temperatures dissolves the [chromates](https://bliptext.com/articles/chromates) and leaves the insoluble iron oxide.\nThe chromate is converted by [sulfuric acid](https://bliptext.com/articles/sulfuric-acid) into the dichromate.\nThe dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.\n# [Piece of chromium produced with aluminothermic reaction | upload.wikimedia.org/wikipedia/commons/c/cf/Chrom///1.jpg]\n# [World production trend of chromium | upload.wikimedia.org/wikipedia/commons/5/5f/Chromium///-///world///production///trend.svg]\n# [Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains | upload.wikimedia.org/wikipedia/commons/4/42/Chromium///zone///refined///and///1cm3///cube.jpg]\n# [Chromium ore output in 2002 | upload.wikimedia.org/wikipedia/commons/2/2c/World///Chromium///Production///2002.svg]\n\n# Applications\nThe creation of metal alloys account for 85% of the available chromium's usage.\nThe remainder of chromium is used in the [chemical](https://bliptext.com/articles/chemical-industry), [refractory](https://bliptext.com/articles/refractory), and [foundry](https://bliptext.com/articles/foundry) industries.\n\n## Metallurgy\nThe strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.\n[High-speed tool steels](https://bliptext.com/articles/high-speed-steel) contain 3–5% chromium.\n[Stainless steel](https://bliptext.com/articles/stainless-steel), the primary corrosion-resistant metal alloy, is formed when chromium is introduced to [iron](https://bliptext.com/articles/iron) in concentrations above 11%.\nFor stainless steel's formation, ferrochromium is added to the molten iron.\nAlso, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries.\nFor example, [Inconel](https://bliptext.com/articles/inconel) 718 contains 18.6% chromium.\nBecause of the excellent high-temperature properties of these nickel [superalloys](https://bliptext.com/articles/superalloy), they are used in [jet engines](https://bliptext.com/articles/jet-engine) and [gas turbines](https://bliptext.com/articles/gas-turbine) in lieu of common structural materials.\n[ASTM](https://bliptext.com/articles/astm) B163 relies on chromium for condenser and heat-exchanger tubes, while [castings](https://bliptext.com/articles/castings) with high strength at elevated temperatures that contain chromium are standardised with [ASTM](https://bliptext.com/articles/astm) A567.\n[AISI](https://bliptext.com/articles/american-iron-and-steel-institute) type 332 is used where high temperature would normally cause [carburization](https://bliptext.com/articles/carburization), [oxidation](https://bliptext.com/articles/oxidation) or [corrosion](https://bliptext.com/articles/corrosion).\n[Incoloy](https://bliptext.com/articles/incoloy) 800 \"is capable of remaining stable and maintaining its [austenitic](https://bliptext.com/articles/austenitic) structure even after long time exposures to high temperatures\".\n[Nichrome](https://bliptext.com/articles/nichrome) is used as resistance wire for heating elements in things like [toasters](https://bliptext.com/articles/toasters) and space heaters.\nThese uses make chromium a [strategic material](https://bliptext.com/articles/strategic-material).\nConsequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it \"may become a critical material during the emergency\".\nThe United States likewise considered chromium \"essential for the German war industry\" and made intense diplomatic efforts to keep it out of the hands of [Nazi Germany](https://bliptext.com/articles/nazi-germany).\nThe high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals.\nA layer of chromium is deposited on pretreated metallic surfaces by [electroplating](https://bliptext.com/articles/electroplating) techniques.\nThere are two deposition methods: thin, and thick.\nThin deposition involves a layer of chromium below 1 μm thickness deposited by [chrome plating](https://bliptext.com/articles/chrome-plating), and is used for decorative surfaces.\nThicker chromium layers are deposited if wear-resistant surfaces are needed.\nBoth methods use acidic chromate or [dichromate](https://bliptext.com/articles/dichromate) solutions.\nTo prevent the energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used.\nIn the [chromate conversion coating](https://bliptext.com/articles/chromate-conversion-coating) process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium.\nThis [passivation](https://bliptext.com/articles/passivation-chemistry) and the self-healing properties of the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.\nBecause of environmental and health regulations on chromates, alternative coating methods are under development.\nChromic acid [anodizing](https://bliptext.com/articles/anodizing) (or Type I [anodizing](https://bliptext.com/articles/anodizing)) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses [chromic acid](https://bliptext.com/articles/chromic-acid) as an electrolyte in the solution.\nDuring anodization, an oxide layer is formed on the aluminium.\nThe use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.\nThe high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least a change to less toxic chromium(III) compounds.\n# [Stainless steel cutlery made from Cromargan 18/10, containing 18% chromium | upload.wikimedia.org/wikipedia/commons/6/66/Besteck///WMF///Stockholm///ca///1960er.jpg]\n# [Decorative chrome plating on a motorcycle | upload.wikimedia.org/wikipedia/commons/e/e1/Motorcycle///Reflections///bw///edit.jpg]\n\n## Pigment\nThe mineral [crocoite](https://bliptext.com/articles/crocoite) (which is also [lead chromate](https://bliptext.com/articles/lead-chromate) PbCrO4) was used as a yellow pigment shortly after its discovery.\nAfter a synthesis method became available starting from the more abundant chromite, [chrome yellow](https://bliptext.com/articles/chrome-yellow) was, together with [cadmium yellow](https://bliptext.com/articles/cadmium-yellow), one of the most used yellow pigments.\nThe pigment does not photodegrade, but it tends to darken due to the formation of chromium(III) oxide.\nIt has a strong color, and was used for school buses in the United States and for the postal services (for example, the [Deutsche Post](https://bliptext.com/articles/deutsche-post)) in Europe.\nThe use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium.\nOther pigments that are based around chromium are, for example, the deep shade of red pigment [chrome red](https://bliptext.com/articles/chrome-red), which is simply lead chromate with [lead(II) hydroxide](https://bliptext.com/articles/lead-ii-hydroxide) (PbCrO4·Pb(OH)2).\nA very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate.\nA wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution.\nThis used zinc tetroxychromate dispersed in a solution of [polyvinyl butyral](https://bliptext.com/articles/polyvinyl-butyral).\nAn 8% solution of phosphoric acid in solvent was added just before application.\nIt was found that an easily oxidized alcohol was an essential ingredient.\nA thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured.\nThere is still a question as to the correct mechanism.\nChrome green is a mixture of [Prussian blue](https://bliptext.com/articles/prussian-blue) and [chrome yellow](https://bliptext.com/articles/chrome-yellow), while the chrome oxide green is [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium oxides are also used as a green pigment in the field of glassmaking and also as a glaze for ceramics.\nGreen chromium oxide is extremely [lightfast](https://bliptext.com/articles/lightfastness) and as such is used in cladding coatings.\nIt is also the main ingredient in [infrared](https://bliptext.com/articles/infrared) reflecting paints, used by the armed forces to paint vehicles and to give them the same [infrared](https://bliptext.com/articles/infrared) reflectance as green leaves.\n\n## Other uses\nChromium(III) ions present in [corundum](https://bliptext.com/articles/corundum) crystals (aluminium oxide) cause them to be colored red; when [corundum](https://bliptext.com/articles/corundum) appears as such, it is known as a [ruby](https://bliptext.com/articles/ruby).\nIf the corundum is lacking in chromium(III) ions, it is known as a [sapphire](https://bliptext.com/articles/sapphire).\nA red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies.\nSuch a synthetic ruby crystal was the basis for the first [laser](https://bliptext.com/articles/laser), produced in 1960, which relied on [stimulated emission](https://bliptext.com/articles/stimulated-emission) of light from the chromium atoms in such a crystal.\nRuby has a laser transition at 694.3 nanometers, in a deep red color.\nChromium(VI) salts are used for the preservation of wood.\nFor example, [chromated copper arsenate](https://bliptext.com/articles/chromated-copper-arsenate) (CCA) is used in [timber treatment](https://bliptext.com/articles/timber-treatment) to protect wood from decay fungi, wood-attacking insects, including [termites](https://bliptext.com/articles/termites), and marine borers.\nThe formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%.\nIn the United States, 65,300 metric tons of CCA solution were used in 1996.\nChromium(III) salts, especially [chrome alum](https://bliptext.com/articles/chrome-alum) and [chromium(III) sulfate](https://bliptext.com/articles/chromium-iii-sulfate), are used in the tanning of [leather](https://bliptext.com/articles/leather).\nThe chromium(III) stabilizes the leather by cross linking the [collagen](https://bliptext.com/articles/collagen) fibers.\nChromium tanned leather can contain 4–5% of chromium, which is tightly bound to the proteins.\nAlthough the form of chromium used for tanning is not the toxic hexavalent variety, there remains interest in management of chromium in the tanning industry.\nRecovery and reuse, direct/indirect recycling, and \"chrome-less\" or \"chrome-free\" tanning are practiced to better manage chromium usage.\nThe high heat resistivity and high melting point makes [chromite](https://bliptext.com/articles/chromite) and chromium(III) oxide a material for high temperature refractory applications, like [blast furnaces](https://bliptext.com/articles/blast-furnace), cement [kilns](https://bliptext.com/articles/kiln), molds for the firing of [bricks](https://bliptext.com/articles/brick) and as foundry sands for the [casting](https://bliptext.com/articles/casting-metalworking) of metals.\nIn these applications, the refractory materials are made from mixtures of chromite and magnesite.\nThe use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).\nSeveral chromium compounds are used as [catalysts](https://bliptext.com/articles/catalyst) for processing hydrocarbons.\nFor example, the [Phillips catalyst](https://bliptext.com/articles/phillips-catalyst), prepared from chromium oxides, is used for the production of about half the world's [polyethylene](https://bliptext.com/articles/polyethylene).\nFe-Cr mixed oxides are employed as high-temperature catalysts for the [water gas shift reaction](https://bliptext.com/articles/water-gas-shift-reaction).\n[Copper chromite](https://bliptext.com/articles/copper-chromite) is a useful [hydrogenation](https://bliptext.com/articles/hydrogenation) catalyst.\n# [Red crystal of a ruby laser | upload.wikimedia.org/wikipedia/commons/7/7d/5///Maiman///Laser///Components.jpg]\n\n## Uses of compounds\n\n# Biological role\nThe possible nutritional value of chromium(III) is unproven.\nAlthough chromium is regarded as a trace element and [dietary mineral](https://bliptext.com/articles/mineral-nutrient), its suspected roles in the action of [insulin](https://bliptext.com/articles/insulin) – a hormone that mediates the metabolism and storage of carbohydrate, fat, and protein – have not been adequately established.\nThe [mechanism of its actions](https://bliptext.com/articles/mechanism-of-action) in the body is undefined, leaving in doubt whether chromium has a biological role in healthy people.\nIn contrast, [hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium) (Cr(VI) or Cr6+) is highly toxic and [mutagenic](https://bliptext.com/articles/mutagen).\nIngestion of chromium(VI) in water has been linked to stomach tumors, and it may also cause allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis).\n\"[Chromium deficiency](https://bliptext.com/articles/chromium-deficiency)\", involving a lack of Cr(III) in the body, or perhaps some complex of it, such as [glucose tolerance factor](https://bliptext.com/articles/glucose-tolerance-factor), is not accepted as a medical condition, as it has no symptoms and healthy people do not require chromium supplementation.\nSome studies suggest that the biologically active form of chromium(III) is transported in the body via an oligopeptide called [low-molecular-weight chromium-binding substance](https://bliptext.com/articles/low-molecular-weight-chromium-binding-substance) (chromodulin), which might play a role in the insulin signaling pathway.\nThe chromium content of common foods is generally low (1–13 micrograms per serving).\nThe chromium content of food varies widely, due to differences in soil mineral content, growing season, plant [cultivar](https://bliptext.com/articles/cultivar), and contamination during processing.\nChromium (and [nickel](https://bliptext.com/articles/nickel)) leach into food cooked in stainless steel, with the effect being largest when the cookware is new.\nAcidic foods that are cooked for many hours also exacerbate this effect.\n\n## Dietary recommendations\nThere is disagreement on chromium's status as an essential nutrient.\nGovernmental departments from Australia, New Zealand, India, and Japan consider chromium as essential, while the United States and European Food Safety Authority of the European Union do not.\nThe U.S. [National Academy of Medicine](https://bliptext.com/articles/national-academy-of-medicine) (NAM) updated the [Estimated Average Requirements](https://bliptext.com/articles/dietary-reference-intake) (EARs) and the [Recommended Dietary Allowances](https://bliptext.com/articles/dietary-reference-intake) (RDAs) for chromium in 2001.\nFor chromium, there was insufficient information to set EARs and RDAs, so its needs are described as estimates for [Adequate Intake](https://bliptext.com/articles/dietary-reference-intake) (AI).\nFrom a 2001 assessment, AI of chromium for women ages 14 through 50 is 25 μg/day, and the AI for women ages 50 and above is 20 μg/day.\nThe AIs for women who are pregnant are 30 μg/day, and for women who are lactating, the set AI is 45 μg/day.\nThe AI for men ages 14 through 50 is 35 μg/day, and the AI for men ages 50 and above is 30 μg/day.\nFor children ages 1 through 13, the AI increases with age from 0.2 μg/day up to 25 μg/day.\nAs for safety, the NAM sets [Tolerable Upper Intake Levels](https://bliptext.com/articles/dietary-reference-intake) (ULs) for vitamins and minerals when the evidence is sufficient.\nIn the case of chromium, there is not yet enough information, hence no UL has been established.\nCollectively, the EARs, RDAs, AIs, and ULs are the parameters for the nutrition recommendation system known as [Dietary Reference Intake](https://bliptext.com/articles/dietary-reference-intake) (DRI).\nAustralia and New Zealand consider chromium to be an essential nutrient, with an AI of 35 μg/day for men, 25 μg/day for women, 30 μg/day for women who are pregnant, and 45 μg/day for women who are lactating.\nA UL has not been set due to the lack of sufficient data.\nIndia considers chromium to be an essential nutrient, with an adult recommended intake of 33 μg/day.\nJapan also considers chromium to be an essential nutrient, with an AI of 10 μg/day for adults, including women who are pregnant or lactating.\nA UL has not been set.\nThe EFSA does not consider chromium to be an essential nutrient.\n\n### Labeling\nFor U.S. food and dietary supplement labeling purposes, the amount of the substance in a serving is expressed as a percent of the [Daily Value](https://bliptext.com/articles/reference-daily-intake) (%DV).\nFor chromium labeling purposes, 100% of the Daily Value was 120 μg. As of 27 May 2016, the percentage of daily value was revised to 35 μg to bring the chromium intake into a consensus with the official [Recommended Dietary Allowance](https://bliptext.com/articles/dietary-reference-intake).\nA table of the old and new adult daily values in the United States is provided at [Reference Daily Intake](https://bliptext.com/articles/reference-daily-intake).\nAfter evaluation of research on the potential nutritional value of chromium, the European Food Safety Authority concluded that there was no evidence of benefit by dietary chromium in healthy people, thereby declining to establish recommendations in Europe for dietary intake of chromium.\n\n## Food sources\nFood composition databases such as those maintained by the U.S. Department of Agriculture do not contain information on the chromium content of foods.\nA wide variety of animal and vegetable foods contain chromium.\nContent per serving is influenced by the chromium content of the soil in which the plants are grown, by foodstuffs fed to animals, and by processing methods, as chromium is leached into foods if processed or cooked in stainless steel equipment.\nOne diet analysis study conducted in Mexico reported an average daily chromium intake of 30 micrograms.\nAn estimated 31% of adults in the United States consume multi-vitamin/mineral dietary supplements, which often contain 25 to 60 micrograms of chromium.\n\n## Supplementation\nChromium is an ingredient in [total parenteral nutrition](https://bliptext.com/articles/total-parenteral-nutrition) (TPN), because deficiency can occur after months of intravenous feeding with chromium-free TPN.\nIt is also added to nutritional products for [preterm infants](https://bliptext.com/articles/preterm-infant).\nAlthough the mechanism of action in biological roles for chromium is unclear, in the United States chromium-containing products are sold as non-prescription dietary supplements in amounts ranging from 50 to 1,000 μg. Lower amounts of chromium are also often incorporated into multi-vitamin/mineral supplements consumed by an estimated 31% of adults in the United States.\nChemical compounds used in dietary supplements include chromium chloride, chromium citrate, [chromium(III) picolinate](https://bliptext.com/articles/chromium-iii-picolinate), [chromium(III) polynicotinate](https://bliptext.com/articles/chromium-polynicotinate), and other chemical compositions.\nThe benefit of supplements has not been proven.\n\n### Initiation of research on glucose\nThe notion of chromium as a potential regulator of glucose metabolism began in the 1950s when scientists performed a series of experiments controlling the diet of rats.\nThe experimenters subjected the rats to a chromium deficient diet, and witnessed an inability to respond effectively to increased levels of blood glucose.\nA chromium-rich [Brewer's yeast](https://bliptext.com/articles/yeast) was provided in the diet, enabling the rats to effectively metabolize glucose, and so giving evidence that chromium may have a role in glucose management.\n\n## Approved and disapproved health claims\nIn 2005, the U.S. Food and Drug Administration had approved a qualified health claim for chromium picolinate with a requirement for specific label wording:\nIn other parts of the petition, the FDA rejected claims for chromium picolinate and cardiovascular disease, retinopathy or kidney disease caused by abnormally high blood sugar levels.\nAs of March 2024, this ruling on chromium remains in effect.\nIn 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements.\nApproved labeling statements include: a factor in the maintenance of good health, provides support for healthy glucose metabolism, helps the body to metabolize carbohydrates and helps the body to metabolize fats.\nThe European Food Safety Authority approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration, but rejected claims for maintenance or achievement of a normal body weight, or reduction of tiredness or fatigue.\nHowever, in a 2014 reassessment of studies to determine whether a Dietary Reference Intake value could be established for chromium, EFSA stated:\n\n### Diabetes\nGiven the evidence for chromium deficiency causing problems with glucose management in the context of intravenous nutrition products formulated without chromium, research interest turned to whether chromium supplementation would benefit people who have type 2 diabetes but are not chromium deficient.\nLooking at the results from four meta-analyses, one reported a statistically significant decrease in fasting [plasma glucose](https://bliptext.com/articles/plasma-glucose) levels and a non-significant trend in lower [hemoglobin A1C](https://bliptext.com/articles/glycated-hemoglobin).\nA second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either.\nA review published in 2016 listed 53 [randomized clinical trials](https://bliptext.com/articles/randomized-clinical-trial) that were included in one or more of six [meta-analyses](https://bliptext.com/articles/meta-analysis).\nIt concluded that whereas there may be modest decreases in fasting blood glucose and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome.\n\n### Body weight\nTwo [systematic reviews](https://bliptext.com/articles/systematic-review) looked at chromium supplements as a mean of managing body weight in overweight and obese people.\nOne, limited to [chromium picolinate](https://bliptext.com/articles/chromium-picolinate), a common supplement ingredient, reported a statistically significant −1.1 kg (2.4 lb) weight loss in trials longer than 12 weeks.\nThe other included all chromium compounds and reported a statistically significant −0.50 kg (1.1 lb) weight change.\nChange in percent body fat did not reach statistical significance.\nAuthors of both reviews considered the clinical relevance of this modest weight loss as uncertain/unreliable.\nThe European Food Safety Authority reviewed the literature and concluded that there was insufficient evidence to support a claim.\n\n### Sports\nChromium is promoted as a sports performance dietary supplement, based on the theory that it potentiates insulin activity, with anticipated results of increased muscle mass, and faster recovery of glycogen storage during post-exercise recovery.\nA review of clinical trials reported that chromium supplementation did not improve exercise performance or increase muscle strength.\nThe International Olympic Committee reviewed dietary supplements for high-performance athletes in 2018 and concluded there was no need to increase chromium intake for athletes, nor support for claims of losing body fat.\n\n## Fresh-water fish\nIrrigation water standards for chromium are 0.1 mg/L, but some rivers in [Bangladesh](https://bliptext.com/articles/bangladesh) are more than five times that amount.\nThe standard for fish for human consumption is less than 1 mg/kg, but many tested samples were more than five times that amount.\nChromium, especially hexavalent chromium, is highly toxic to fish because it is easily absorbed across the gills, readily enters blood circulation, crosses cell membranes and bioconcentrates up the food chain.\nIn contrast, the toxicity of trivalent chromium is very low, attributed to poor membrane permeability and little biomagnification.\nAcute and chronic exposure to chromium(VI) affects fish behavior, physiology, reproduction and survival.\nHyperactivity and erratic swimming have been reported in contaminated environments.\nEgg hatching and fingerling survival are affected.\nIn adult fish there are reports of histopathological damage to liver, kidney, muscle, intestines, and gills.\nMechanisms include mutagenic gene damage and disruptions of enzyme functions.\nThere is evidence that fish may not require chromium, but benefit from a measured amount in diet.\nIn one study, juvenile fish gained weight on a zero chromium diet, but the addition of 500 μg of chromium in the form of chromium chloride or other supplement types, per kilogram of food (dry weight), increased weight gain.\nAt 2,000 μg/kg the weight gain was no better than with the zero chromium diet, and there were increased DNA strand breaks.\n\n# Precautions\nWater-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.\nBecause of the specific [transport](https://bliptext.com/articles/transport-protein) mechanisms, only limited amounts of chromium(III) enter the cells.\nAcute oral toxicity ranges between 50 and 150 mg/kg.\nA 2008 review suggested that moderate uptake of chromium(III) through dietary supplements poses no genetic-toxic risk.\nIn the US, the [Occupational Safety and Health Administration](https://bliptext.com/articles/occupational-safety-and-health-administration) (OSHA) has designated an air [permissible exposure limit](https://bliptext.com/articles/permissible-exposure-limit) (PEL) in the workplace as a time-weighted average (TWA) of 1 mg/m3.\nThe [National Institute for Occupational Safety and Health](https://bliptext.com/articles/national-institute-for-occupational-safety-and-health) (NIOSH) has set a [recommended exposure limit](https://bliptext.com/articles/recommended-exposure-limit) (REL) of 0.5 mg/m3, time-weighted average.\nThe [IDLH](https://bliptext.com/articles/idlh) (immediately dangerous to life and health) value is 250 mg/m3.\n\n## Chromium(VI) toxicity\nThe acute [oral](https://bliptext.com/articles/mouth) [toxicity](https://bliptext.com/articles/toxicity) for [chromium(VI)](https://bliptext.com/articles/hexavalent-chromium) ranges between 1.5 and 3.3 mg/kg.\nIn the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells.\nThe chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also [sulfate](https://bliptext.com/articles/sulfate) and [phosphate](https://bliptext.com/articles/phosphate) ions enter the cell.\nThe acute toxicity of chromium(VI) is due to its strong [oxidant](https://bliptext.com/articles/redox) properties.\nAfter it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions.\n[Hemolysis](https://bliptext.com/articles/hemolysis), [renal](https://bliptext.com/articles/renal), and liver failure result.\nAggressive dialysis can be therapeutic.\nThe [carcinogenity](https://bliptext.com/articles/carcinogenity) of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.\nThree mechanisms have been proposed to describe the [genotoxicity](https://bliptext.com/articles/genotoxicity) of chromium(VI).\nThe first mechanism includes highly reactive [hydroxyl radicals](https://bliptext.com/articles/hydroxyl-radical) and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III).\nThe second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the [DNA](https://bliptext.com/articles/dna).\nThe last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.\nChromium salts (chromates) are also the cause of [allergic reactions](https://bliptext.com/articles/allergic-reaction) in some people.\nChromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.\nContact with products containing chromates can lead to allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis) and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as \"chrome ulcers\".\nThis condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.\n\n## Environmental issues\nBecause chromium compounds were used in [dyes](https://bliptext.com/articles/dye), [paints](https://bliptext.com/articles/paint), and [leather](https://bliptext.com/articles/leather) [tanning](https://bliptext.com/articles/tanning-leather) compounds, these compounds are often found in soil and [groundwater](https://bliptext.com/articles/groundwater) at active and abandoned industrial sites, needing [environmental cleanup](https://bliptext.com/articles/environmental-cleanup) and [remediation](https://bliptext.com/articles/environmental-remediation).\n[Primer paint](https://bliptext.com/articles/primer-paint) containing hexavalent chromium is still widely used for [aerospace](https://bliptext.com/articles/aerospace) and [automobile](https://bliptext.com/articles/automobile) refinishing applications.\nIn 2010, the [Environmental Working Group](https://bliptext.com/articles/environmental-working-group) studied the drinking water in 35 American cities in the first nationwide study.\nThe study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with [Norman, Oklahoma](https://bliptext.com/articles/norman-oklahoma), at the top of list; 25 cities had levels that exceeded California's proposed limit.\nThe more toxic hexavalent chromium form can be reduced to the less soluble trivalent oxidation state in soils by organic matter, ferrous iron, sulfides, and other reducing agents, with the rates of such reduction being faster under more acidic conditions than under more alkaline ones.\nIn contrast, trivalent chromium can be oxidized to hexavalent chromium in soils by manganese oxides, such as Mn(III) and Mn(IV) compounds.\nSince the solubility and toxicity of chromium (VI) are greater that those of chromium (III), the oxidation-reduction conversions between the two oxidation states have implications for movement and bioavailability of chromium in soils, groundwater, and plants.\n\n# General bibliography","wordIndex":785,"createdAt":"2025-03-18T15:15:13.297Z","user":{"id":"jr9320kzLD37CkxadNfMG9YBINNdhTeS","name":"The Raters","image":"https://lh3.googleusercontent.com/a/ACg8ocIdQIQQjHI233tCJ_h-vtFv9t351nMGaL3Sfolwv8P7mLg2Ez0=s96-c"}},{"id":"607e3d96-4649-4cec-b5b9-a9c2219257e8","wordChanged":"chromium's","newWord":":::summary\n**Vickers Hardness:** 950HV \n**Vickers Hardness Ref:** https://www.journalmt.com/pdfs/mft/2018/04/16.pdf \n:::\n\n# \n**Chromium** is a [chemical element](https://bliptext.com/articles/chemical-element); it has [symbol](https://bliptext.com/articles/symbol-chemistry) **Cr** and [atomic number](https://bliptext.com/articles/atomic-number) 24.\nIt is the first element in [group 6](https://bliptext.com/articles/group-6-element).\nIt is a steely-grey, [lustrous](https://bliptext.com/articles/luster-mineralogy), hard, and brittle [transition metal](https://bliptext.com/articles/transition-metal).\nChromium is valued for its high [corrosion](https://bliptext.com/articles/corrosion) resistance and [hardness](https://bliptext.com/articles/hardness).\nA major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form [stainless steel](https://bliptext.com/articles/stainless-steel).\nStainless steel and [chrome plating](https://bliptext.com/articles/chrome-plating) ([electroplating](https://bliptext.com/articles/electroplating) with chromium) together comprise 85% of the commercial use.\nChromium is also greatly valued as a [metal](https://bliptext.com/articles/metal) that is able to be highly [polished](https://bliptext.com/articles/polishing) while resisting [tarnishing](https://bliptext.com/articles/tarnish).\nPolished chromium reflects almost 70% of the [visible spectrum](https://bliptext.com/articles/visible-spectrum), and almost 90% of [infrared light](https://bliptext.com/articles/infrared).\nThe name of the element is derived from the [Greek](https://bliptext.com/articles/ancient-greek) word χρῶμα, chrōma, meaning [color](https://bliptext.com/articles/color), because many chromium compounds are intensely [color](https://bliptext.com/articles/color)ed.\nIndustrial production of chromium proceeds from [chromite](https://bliptext.com/articles/chromite) ore (mostly FeCr2O4) to produce [ferrochromium](https://bliptext.com/articles/ferrochromium), an iron-chromium alloy, by means of [aluminothermic](https://bliptext.com/articles/aluminothermic-reaction) or [silicothermic reactions](https://bliptext.com/articles/silicothermic-reaction).\nFerrochromium is then used to produce alloys such as stainless steel.\nPure chromium metal is produced by a different process: [roasting](https://bliptext.com/articles/roasting-metallurgy) and [leaching](https://bliptext.com/articles/leaching-metallurgy) of chromite to separate it from iron, followed by reduction with [carbon](https://bliptext.com/articles/carbon) and then [aluminium](https://bliptext.com/articles/aluminium).\n[Trivalent](https://bliptext.com/articles/trivalent) chromium (Cr(III)) occurs naturally in many foods and is sold as a [dietary supplement](https://bliptext.com/articles/dietary-supplement), although there is insufficient evidence that dietary chromium provides nutritional benefit to people.\nIn 2014, the [European Food Safety Authority](https://bliptext.com/articles/european-food-safety-authority) concluded that research on dietary chromium did not justify it to be recognized as an essential [nutrient](https://bliptext.com/articles/nutrient).\nWhile chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called \"[hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium)\", is toxic and [carcinogenic](https://bliptext.com/articles/carcinogenic).\nAccording to the European Chemicals Agency (ECHA), [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) that is used in industrial electroplating processes is a \"substance of very high concern\" (SVHC).\n\n# Physical properties\n\n## Atomic\nGaseous chromium has a ground-state [electron configuration](https://bliptext.com/articles/electron-configuration) of [ [Ar](https://bliptext.com/articles/argon)] 3d5 4s1.\nIt is the first element in the periodic table whose configuration violates the [Aufbau principle](https://bliptext.com/articles/aufbau-principle).\nExceptions to the principle also occur later in the periodic table for elements such as [copper](https://bliptext.com/articles/copper), [niobium](https://bliptext.com/articles/niobium) and [molybdenum](https://bliptext.com/articles/molybdenum).\nChromium is the first element in the 3d series where the 3d electrons start to sink into the core; they thus contribute less to [metallic bonding](https://bliptext.com/articles/metallic-bonding), and hence the melting and boiling points and the [enthalpy of atomisation](https://bliptext.com/articles/enthalpy-of-atomisation) of chromium are lower than those of the preceding element [vanadium](https://bliptext.com/articles/vanadium).\nChromium(VI) is a strong [oxidising agent](https://bliptext.com/articles/oxidising-agent) in contrast to the [molybdenum](https://bliptext.com/articles/molybdenum)(VI) and [tungsten](https://bliptext.com/articles/tungsten)(VI) oxides.\n\n## Bulk\nChromium is the third hardest element after [carbon](https://bliptext.com/articles/carbon) ([diamond](https://bliptext.com/articles/diamond)) and [boron](https://bliptext.com/articles/boron).\nIts [Mohs hardness](https://bliptext.com/articles/mohs-scale-of-mineral-hardness) is 8.5, which means that it can scratch samples of [quartz](https://bliptext.com/articles/quartz) and [topaz](https://bliptext.com/articles/topaz), but can be scratched by [corundum](https://bliptext.com/articles/corundum).\nChromium is highly resistant to [tarnishing](https://bliptext.com/articles/tarnish), which makes it useful as a metal that preserves its outermost layer from [corroding](https://bliptext.com/articles/corrosion), unlike other metals such as [copper](https://bliptext.com/articles/copper), [magnesium](https://bliptext.com/articles/magnesium), and [aluminium](https://bliptext.com/articles/aluminium).\nChromium has a [melting point](https://bliptext.com/articles/melting-point) of 1907 °C (3465 °F), which is relatively low compared to the majority of transition metals.\nHowever, it still has the second highest melting point out of all the [period 4 elements](https://bliptext.com/articles/period-4-element), being topped by [vanadium](https://bliptext.com/articles/vanadium) by 3 °C (5 °F) at 1910 °C (3470 °F).\nThe [boiling point](https://bliptext.com/articles/boiling-point) of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest [boiling point](https://bliptext.com/articles/boiling-point) out of the [Period 4](https://bliptext.com/articles/period-4) [transition metals](https://bliptext.com/articles/transition-metal) alone behind [copper](https://bliptext.com/articles/copper), [manganese](https://bliptext.com/articles/manganese) and [zinc](https://bliptext.com/articles/zinc).\nThe [electrical resistivity](https://bliptext.com/articles/electrical-resistivity-and-conductivity) of chromium at 20 °C is 125 [nanoohm](https://bliptext.com/articles/ohm)-[meters](https://bliptext.com/articles/meter).\nChromium has a high [specular reflection](https://bliptext.com/articles/specular-reflection) in comparison to other transition metals.\nIn [infrared](https://bliptext.com/articles/infrared), at 425 [μm](https://bliptext.com/articles/micrometre), chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 [μm](https://bliptext.com/articles/micrometre) before rising again to 90% at 4000 [μm](https://bliptext.com/articles/micrometre).\nWhen chromium is used in [stainless steel](https://bliptext.com/articles/stainless-steel) alloys and [polished](https://bliptext.com/articles/polishing), the specular reflection decreases with the inclusion of additional metals, yet is still high in comparison with other alloys.\nBetween 40% and 60% of the visible spectrum is reflected from polished stainless steel.\nThe explanation on why chromium displays such a high turnout of reflected [photon](https://bliptext.com/articles/photon) waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties.\nChromium has unique magnetic properties; it is the only elemental solid that shows [antiferromagnetic](https://bliptext.com/articles/antiferromagnetic) ordering at room temperature and below.\nAbove 38 °C, its magnetic ordering becomes [paramagnetic](https://bliptext.com/articles/paramagnetic).\nThe antiferromagnetic properties, which cause the chromium atoms to temporarily [ionize](https://bliptext.com/articles/ionization) and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the [lattice periodicity](https://bliptext.com/articles/crystal-structure).\nThis is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers.\nFrom here, the frequency-dependent [relative permittivity](https://bliptext.com/articles/relative-permittivity) of chromium, deriving from [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations) and Chromakopia [antiferromagnetism](https://bliptext.com/articles/antiferromagnetism), leaves chromium with a high infrared and visible light reflectance.\n# [Sample of chromium metal | upload.wikimedia.org/wikipedia/commons/a/a1/Chromium.jpg]\n\n### Passivation\nChromium metal in air is [passivated](https://bliptext.com/articles/passivation-chemistry): it forms a thin, protective surface layer of chromium oxide with the [corundum](https://bliptext.com/articles/corundum-structure) structure.\nPassivation can be enhanced by short contact with [oxidizing acids](https://bliptext.com/articles/oxidizing-acid) like [nitric acid](https://bliptext.com/articles/nitric-acid).\nPassivated chromium is stable against acids.\nPassivation can be removed with a strong [reducing agent](https://bliptext.com/articles/reducing-agent) that destroys the protective oxide layer on the metal.\nChromium metal treated in this way readily dissolves in weak acids.\nThe surface [chromia](https://bliptext.com/articles/chromium-iii-oxide) Cr2O3 scale, is adherent to the metal.\nIn contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued [rusting](https://bliptext.com/articles/rust).\nAt room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward [diffusion](https://bliptext.com/articles/atomic-diffusion) of metal ions across the scale.\nAbove 950 °C volatile [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) CrO3 forms from the chromia scale, limiting the scale thickness and oxidation protection.\nChromium, unlike iron and nickel, does not suffer from [hydrogen embrittlement](https://bliptext.com/articles/hydrogen-embrittlement).\nHowever, it does suffer from nitrogen [embrittlement](https://bliptext.com/articles/embrittlement), reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.\n\n## Isotopes\nNaturally occurring chromium is composed of four stable [isotopes](https://bliptext.com/articles/isotope); 50Cr, 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% [natural abundance](https://bliptext.com/articles/natural-abundance)).\n50Cr is [observationally stable](https://bliptext.com/articles/stable-nuclide), as it is theoretically capable of [decaying](https://bliptext.com/articles/radioactive-decay) to [50Ti](https://bliptext.com/articles/isotopes-of-titanium) via [double electron capture](https://bliptext.com/articles/double-electron-capture) with a [half-life](https://bliptext.com/articles/half-life) of no less than 1.3 years.\nTwenty-five [radioisotopes](https://bliptext.com/articles/radioisotope) have been characterized, ranging from 42Cr to 70Cr; the most stable radioisotope is 51Cr with a half-life of 27.7 days.\nAll of the remaining [radioactive](https://bliptext.com/articles/radioactive) isotopes have half-lives that are less than 24 hours and the majority less than 1 minute.\nChromium also has two [metastable](https://bliptext.com/articles/metastable) [nuclear isomers](https://bliptext.com/articles/nuclear-isomer).\nThe primary [decay mode](https://bliptext.com/articles/decay-mode) before the most abundant stable isotope, 52Cr, is [electron capture](https://bliptext.com/articles/electron-capture) and the primary mode after is [beta decay](https://bliptext.com/articles/beta-decay).\n53Cr is the [radiogenic](https://bliptext.com/articles/radiogenic) decay product of 53[Mn](https://bliptext.com/articles/manganese) (half-life 3.74 million years).\nChromium isotopes are typically collocated (and compounded) with [manganese](https://bliptext.com/articles/manganese) isotopes.\nThis circumstance is useful in [isotope geology](https://bliptext.com/articles/isotope-geology).\nManganese-chromium isotope ratios reinforce the evidence from [26Al](https://bliptext.com/articles/aluminium-26) and 107[Pd](https://bliptext.com/articles/palladium) concerning the early history of the [Solar System](https://bliptext.com/articles/solar-system).\nVariations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies.\nHence 53Cr provides additional evidence for [nucleosynthetic](https://bliptext.com/articles/nucleosynthesis) processes immediately before coalescence of the Solar System.\n53Cr has been posited as a proxy for atmospheric oxygen concentration.\n\n# Chemistry and compounds\nChromium is a member of [group 6](https://bliptext.com/articles/group-6-element), of the [transition metals](https://bliptext.com/articles/transition-metal).\nThe +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.\n# [The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide | upload.wikimedia.org/wikipedia/commons/c/c3/Chromium///in///water///pourbiax///diagram.png]\n\n## Common oxidation states\n\n### Chromium(0)\nMany Cr(0) complexes are known.\n[Bis(benzene)chromium](https://bliptext.com/articles/bis-benzene-chromium) and [chromium hexacarbonyl](https://bliptext.com/articles/chromium-hexacarbonyl) are highlights in [organochromium chemistry](https://bliptext.com/articles/organochromium-chemistry).\n\n### Chromium(II)\nChromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air.\nWater-stable [chromium(II) chloride](https://bliptext.com/articles/chromium-ii-chloride) that can be made by reducing chromium(III) chloride with zinc.\nThe resulting bright blue solution created from dissolving chromium(II) chloride is stable at neutral [pH](https://bliptext.com/articles/ph).\nSome other notable chromium(II) compounds include [chromium(II) oxide](https://bliptext.com/articles/chromium-ii-oxide), and [chromium(II) sulfate](https://bliptext.com/articles/chromium-ii-sulfate).\nMany chromium(II) carboxylates are known.\nThe red [chromium(II) acetate](https://bliptext.com/articles/chromium-ii-acetate) (Cr2(O2CCH3)4) is somewhat famous.\nIt features a Cr-Cr [quadruple bond](https://bliptext.com/articles/quadruple-bond).\n# [Chromium(II) carbide (Cr3C2) | upload.wikimedia.org/wikipedia/commons/e/eb/Chromium///carbide///Cr3C2.JPG]\n\n### Chromium(III)\nA large number of chromium(III) compounds are known, such as [chromium(III) nitrate](https://bliptext.com/articles/chromium-nitrate), [chromium(III) acetate](https://bliptext.com/articles/chromium-iii-acetate), and [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium(III) can be obtained by dissolving elemental chromium in acids like [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid) or [sulfuric acid](https://bliptext.com/articles/sulfuric-acid), but it can also be formed through the reduction of chromium(VI) by [cytochrome](https://bliptext.com/articles/cytochrome) [c7](https://bliptext.com/articles/cytochrome-c).\nThe ion has a similar radius (63 [pm](https://bliptext.com/articles/picometer)) to (radius 50 [pm](https://bliptext.com/articles/picometer)), and they can replace each other in some compounds, such as in [chrome [alum](https://bliptext.com/articles/alum)](https://bliptext.com/articles/chrome-[alum](https://bliptext.com/articles/alum)) and [alum](https://bliptext.com/articles/alum).\nChromium(III) tends to form [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) complexes.\nCommercially available [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) hydrate is the dark green complex [CrCl2(H2O)4]Cl.\nClosely related compounds are the pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.\nIf anhydrous violet [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) is dissolved in water, the violet solution turns green after some time as the chloride in the inner [coordination sphere](https://bliptext.com/articles/coordination-sphere) is replaced by water.\nThis kind of reaction is also observed with solutions of [chrome alum](https://bliptext.com/articles/chrome-alum) and other water-soluble chromium(III) salts.\nA [tetrahedral](https://bliptext.com/articles/tetrahedral-molecular-geometry) coordination of [chromium(III)](https://bliptext.com/articles/chromium-iii) has been reported for the Cr-centered [Keggin](https://bliptext.com/articles/keggin-structure) anion [α-CrW12O40]5–.\n[Chromium(III) hydroxide](https://bliptext.com/articles/chromium-iii-hydroxide) (Cr(OH)3) is [amphoteric](https://bliptext.com/articles/amphoterism), dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form.\nIt is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), a stable oxide with a crystal structure identical to that of [corundum](https://bliptext.com/articles/corundum).\n# [Anhydrous chromium(III) chloride (CrCl3) | upload.wikimedia.org/wikipedia/commons/3/3b/Chromium%28III%29-chloride-purple-anhydrous-sunlight.jpg]\n\n### Chromium(VI)\n[Chromium(VI) compounds](https://bliptext.com/articles/hexavalent-chromium) are oxidants at low or neutral pH.\n[Chromate](https://bliptext.com/articles/chromate-and-[dichromate](https://bliptext.com/articles/chromate-and-dichromate)) anions and [dichromate](https://bliptext.com/articles/chromate-and-dichromate) (Cr2O72−) anions are the principal ions at this oxidation state.\nThey exist at an equilibrium, determined by pH:\nChromium(VI) oxyhalides are known also and include [chromyl fluoride](https://bliptext.com/articles/chromyl-fluoride) (CrO2F2) and [chromyl chloride](https://bliptext.com/articles/chromyl-chloride).\nHowever, despite several erroneous claims, [chromium hexafluoride](https://bliptext.com/articles/chromium-hexafluoride) (as well as all higher hexahalides) remains unknown, as of 2020.\n[Sodium chromate](https://bliptext.com/articles/sodium-chromate) is produced industrially by the oxidative roasting of [chromite](https://bliptext.com/articles/chromite) ore with [sodium carbonate](https://bliptext.com/articles/sodium-carbonate).\nThe change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of [potassium chromate](https://bliptext.com/articles/potassium-chromate).\nAt yet lower pH values, further condensation to more complex [oxyanions](https://bliptext.com/articles/oxyanion) of chromium is possible.\nBoth the [chromate and dichromate](https://bliptext.com/articles/chromate-and-dichromate) anions are strong oxidizing reagents at low pH:\nThey are, however, only moderately oxidizing at high pH:\nChromium(VI) compounds in solution can be detected by adding an acidic [hydrogen peroxide](https://bliptext.com/articles/hydrogen-peroxide) solution.\nThe unstable dark blue [chromium(VI) peroxide](https://bliptext.com/articles/chromium-vi-peroxide) (CrO5) is formed, which can be stabilized as an ether adduct.\n[Chromic acid](https://bliptext.com/articles/chromic-acid) has the hypothetical formula.\nIt is a vaguely described chemical, despite many well-defined chromates and dichromates being known.\nThe dark red [chromium(VI) oxide](https://bliptext.com/articles/chromium-vi-oxide), the acid [anhydride](https://bliptext.com/articles/anhydride) of chromic acid, is sold industrially as \"chromic acid\".\nIt can be produced by mixing sulfuric acid with dichromate and is a strong oxidizing agent.\n# [Chromium(VI) oxide | upload.wikimedia.org/wikipedia/commons/1/1e/Chrom%28VI%29-oxid.jpg]\n# [Sodium chromate (Na2CrO4) | upload.wikimedia.org/wikipedia/commons/5/51/Chroman///sodn%C3%BD.JPG]\n\n## Other oxidation states\nCompounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate.\nThe only binary compound is the volatile [chromium(V) fluoride](https://bliptext.com/articles/chromium-v-fluoride) (CrF5).\nThis red solid has a melting point of 30 °C and a boiling point of 117 °C.\nIt can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure.\nThe peroxochromate(V) is another example of the +5 oxidation state.\n[Potassium peroxochromate](https://bliptext.com/articles/potassium-tetraperoxochromate-v) (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures.\nThis red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.\nCompounds of chromium(IV) are slightly more common than those of chromium(V).\nThe tetrahalides, [CrF4](https://bliptext.com/articles/chromium-iv-fluoride), [CrCl4](https://bliptext.com/articles/chromium-iv-chloride), and CrBr4, can be produced by treating the trihalides with the corresponding halogen at elevated temperatures.\nSuch compounds are susceptible to disproportionation reactions and are not stable in water.\nOrganic compounds containing Cr(IV) state such as chromium tetra t-butoxide are also known.\nMost chromium(I) compounds are obtained solely by oxidation of electron-rich, [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) chromium(0) complexes.\nOther chromium(I) complexes contain [cyclopentadienyl](https://bliptext.com/articles/cyclopentadienyl) ligands.\nAs verified by [X-ray diffraction](https://bliptext.com/articles/x-ray-diffraction), a Cr-Cr [quintuple bond](https://bliptext.com/articles/quintuple-bond) (length 183.51(4) pm) has also been described.\nExtremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.\n# [Chromium compound determined experimentally to contain a Cr-Cr quintuple bond | upload.wikimedia.org/wikipedia/commons/6/60/5-fold///chromium.png]\n\n# Occurrence\nChromium is the 21st most [abundant element in Earth's crust](https://bliptext.com/articles/abundance-of-elements-in-earth-s-crust) with an average concentration of 100 ppm.\nChromium compounds are found in the environment from the [erosion](https://bliptext.com/articles/erosion) of chromium-containing rocks, and can be redistributed by volcanic eruptions.\nTypical background concentrations of chromium in environmental media are: atmosphere <10 ng/m3; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg.\nChromium is mined as chromite (FeCr2O4) ore.\nAbout two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers.\nUntapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.\nAlthough rare, deposits of [native](https://bliptext.com/articles/native-metal) chromium exist.\nThe [Udachnaya Pipe](https://bliptext.com/articles/udachnaya-pipe) in Russia produces samples of the native metal.\nThis mine is a [kimberlite](https://bliptext.com/articles/kimberlite) pipe, rich in [diamonds](https://bliptext.com/articles/diamond), and the [reducing environment](https://bliptext.com/articles/redox) helped produce both elemental chromium and [diamonds](https://bliptext.com/articles/diamond).\nThe relation between Cr(III) and Cr(VI) strongly depends on [pH](https://bliptext.com/articles/ph) and [oxidative](https://bliptext.com/articles/oxidative) properties of the location.\nIn most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L is Cr(VI).\n# [Crocoite (PbCrO4) | upload.wikimedia.org/wikipedia/commons/a/ac/Crocoite///from///Tasmania.jpg]\n# [Chromite ore | upload.wikimedia.org/wikipedia/commons/0/00/Chromit///1.jpg]\n\n# History\n\n## Early applications\nChromium minerals as pigments came to the attention of the west in the eighteenth century.\nOn 26 July 1761, [Johann Gottlob Lehmann](https://bliptext.com/articles/johann-gottlob-lehmann-scientist) found an orange-red mineral in the [Beryozovskoye mines](https://bliptext.com/articles/beryozovskoye-deposit) in the [Ural Mountains](https://bliptext.com/articles/ural-mountains) which he named Siberian red lead.\nThough misidentified as a [lead](https://bliptext.com/articles/lead) compound with [selenium](https://bliptext.com/articles/selenium) and [iron](https://bliptext.com/articles/iron) components, the mineral was in fact [crocoite](https://bliptext.com/articles/crocoite) with a formula of PbCrO4.\nIn 1770, [Peter Simon Pallas](https://bliptext.com/articles/peter-simon-pallas) visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a [pigment](https://bliptext.com/articles/pigment) in [paints](https://bliptext.com/articles/paint).\nAfter Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region.\nCrocoite would be the principal source of chromium in pigments until the discovery of [chromite](https://bliptext.com/articles/chromite) many years later.\nIn 1794, [Louis Nicolas Vauquelin](https://bliptext.com/articles/louis-nicolas-vauquelin) received samples of crocoite [ore](https://bliptext.com/articles/ore).\nHe produced [chromium trioxide](https://bliptext.com/articles/chromium-vi-oxide) (CrO3) by mixing crocoite with [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid).\nIn 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.\nVauquelin was also able to detect traces of chromium in precious [gemstones](https://bliptext.com/articles/gemstone), such as [ruby](https://bliptext.com/articles/ruby) and [emerald](https://bliptext.com/articles/emerald).\nDuring the nineteenth century, chromium was primarily used not only as a component of paints, but in [tanning](https://bliptext.com/articles/tanning-leather) salts as well.\nFor quite some time, the crocoite found in Russia was the main source for such tanning materials.\nIn 1827, a larger chromite deposit was discovered near [Baltimore](https://bliptext.com/articles/baltimore), United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.\nThis made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of [Bursa](https://bliptext.com/articles/bursa), Turkey.\nWith the development of metallurgy and chemical industries in the Western world, the need for chromium increased.\nChromium is also famous for its reflective, metallic luster when polished.\nIt is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by [electroplating](https://bliptext.com/articles/electroplating).\nChromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.\n# [The red color of rubies is due to trace amounts of chromium within the corundum. | upload.wikimedia.org/wikipedia/commons/c/c4/Cut///Ruby.jpg]\n\n# Production\nApproximately 28.8 million metric tons (Mt) of marketable chromite ore was produced in 2013, and converted into 7.5 Mt of ferrochromium.\nAccording to John F. Papp, writing for the USGS, \"Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium.\"\nThe largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing the rest of about 18% of the world production.\nThe two main products of chromium ore refining are [ferrochromium](https://bliptext.com/articles/ferrochromium) and metallic chromium.\nFor those products the ore smelter process differs considerably.\nFor the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in [electric arc furnace](https://bliptext.com/articles/electric-arc-furnace) or in smaller smelters with either [aluminium](https://bliptext.com/articles/aluminium) or [silicon](https://bliptext.com/articles/silicon) in an [aluminothermic reaction](https://bliptext.com/articles/aluminothermic-reaction).\nFor the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process.\nThe chromite ore is heated with a mixture of [calcium carbonate](https://bliptext.com/articles/calcium-carbonate) and [sodium carbonate](https://bliptext.com/articles/sodium-carbonate) in the presence of air.\nThe chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.\nThe subsequent leaching at higher elevated temperatures dissolves the [chromates](https://bliptext.com/articles/chromates) and leaves the insoluble iron oxide.\nThe chromate is converted by [sulfuric acid](https://bliptext.com/articles/sulfuric-acid) into the dichromate.\nThe dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.\n# [Piece of chromium produced with aluminothermic reaction | upload.wikimedia.org/wikipedia/commons/c/cf/Chrom///1.jpg]\n# [World production trend of chromium | upload.wikimedia.org/wikipedia/commons/5/5f/Chromium///-///world///production///trend.svg]\n# [Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains | upload.wikimedia.org/wikipedia/commons/4/42/Chromium///zone///refined///and///1cm3///cube.jpg]\n# [Chromium ore output in 2002 | upload.wikimedia.org/wikipedia/commons/2/2c/World///Chromium///Production///2002.svg]\n\n# Applications\nThe creation of metal alloys account for 85% of the available chromium's usage.\nThe remainder of chromium is used in the [chemical](https://bliptext.com/articles/chemical-industry), [refractory](https://bliptext.com/articles/refractory), and [foundry](https://bliptext.com/articles/foundry) industries.\n\n## Metallurgy\nThe strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.\n[High-speed tool steels](https://bliptext.com/articles/high-speed-steel) contain 3–5% chromium.\n[Stainless steel](https://bliptext.com/articles/stainless-steel), the primary corrosion-resistant metal alloy, is formed when chromium is introduced to [iron](https://bliptext.com/articles/iron) in concentrations above 11%.\nFor stainless steel's formation, ferrochromium is added to the molten iron.\nAlso, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries.\nFor example, [Inconel](https://bliptext.com/articles/inconel) 718 contains 18.6% chromium.\nBecause of the excellent high-temperature properties of these nickel [superalloys](https://bliptext.com/articles/superalloy), they are used in [jet engines](https://bliptext.com/articles/jet-engine) and [gas turbines](https://bliptext.com/articles/gas-turbine) in lieu of common structural materials.\n[ASTM](https://bliptext.com/articles/astm) B163 relies on chromium for condenser and heat-exchanger tubes, while [castings](https://bliptext.com/articles/castings) with high strength at elevated temperatures that contain chromium are standardised with [ASTM](https://bliptext.com/articles/astm) A567.\n[AISI](https://bliptext.com/articles/american-iron-and-steel-institute) type 332 is used where high temperature would normally cause [carburization](https://bliptext.com/articles/carburization), [oxidation](https://bliptext.com/articles/oxidation) or [corrosion](https://bliptext.com/articles/corrosion).\n[Incoloy](https://bliptext.com/articles/incoloy) 800 \"is capable of remaining stable and maintaining its [austenitic](https://bliptext.com/articles/austenitic) structure even after long time exposures to high temperatures\".\n[Nichrome](https://bliptext.com/articles/nichrome) is used as resistance wire for heating elements in things like [toasters](https://bliptext.com/articles/toasters) and space heaters.\nThese uses make chromium a [strategic material](https://bliptext.com/articles/strategic-material).\nConsequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it \"may become a critical material during the emergency\".\nThe United States likewise considered chromium \"essential for the German war industry\" and made intense diplomatic efforts to keep it out of the hands of [Nazi Germany](https://bliptext.com/articles/nazi-germany).\nThe high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals.\nA layer of chromium is deposited on pretreated metallic surfaces by [electroplating](https://bliptext.com/articles/electroplating) techniques.\nThere are two deposition methods: thin, and thick.\nThin deposition involves a layer of chromium below 1 μm thickness deposited by [chrome plating](https://bliptext.com/articles/chrome-plating), and is used for decorative surfaces.\nThicker chromium layers are deposited if wear-resistant surfaces are needed.\nBoth methods use acidic chromate or [dichromate](https://bliptext.com/articles/dichromate) solutions.\nTo prevent the energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used.\nIn the [chromate conversion coating](https://bliptext.com/articles/chromate-conversion-coating) process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium.\nThis [passivation](https://bliptext.com/articles/passivation-chemistry) and the self-healing properties of the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.\nBecause of environmental and health regulations on chromates, alternative coating methods are under development.\nChromic acid [anodizing](https://bliptext.com/articles/anodizing) (or Type I [anodizing](https://bliptext.com/articles/anodizing)) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses [chromic acid](https://bliptext.com/articles/chromic-acid) as an electrolyte in the solution.\nDuring anodization, an oxide layer is formed on the aluminium.\nThe use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.\nThe high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least a change to less toxic chromium(III) compounds.\n# [Stainless steel cutlery made from Cromargan 18/10, containing 18% chromium | upload.wikimedia.org/wikipedia/commons/6/66/Besteck///WMF///Stockholm///ca///1960er.jpg]\n# [Decorative chrome plating on a motorcycle | upload.wikimedia.org/wikipedia/commons/e/e1/Motorcycle///Reflections///bw///edit.jpg]\n\n## Pigment\nThe mineral [crocoite](https://bliptext.com/articles/crocoite) (which is also [lead chromate](https://bliptext.com/articles/lead-chromate) PbCrO4) was used as a yellow pigment shortly after its discovery.\nAfter a synthesis method became available starting from the more abundant chromite, [chrome yellow](https://bliptext.com/articles/chrome-yellow) was, together with [cadmium yellow](https://bliptext.com/articles/cadmium-yellow), one of the most used yellow pigments.\nThe pigment does not photodegrade, but it tends to darken due to the formation of chromium(III) oxide.\nIt has a strong color, and was used for school buses in the United States and for the postal services (for example, the [Deutsche Post](https://bliptext.com/articles/deutsche-post)) in Europe.\nThe use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium.\nOther pigments that are based around chromium are, for example, the deep shade of red pigment [chrome red](https://bliptext.com/articles/chrome-red), which is simply lead chromate with [lead(II) hydroxide](https://bliptext.com/articles/lead-ii-hydroxide) (PbCrO4·Pb(OH)2).\nA very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate.\nA wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution.\nThis used zinc tetroxychromate dispersed in a solution of [polyvinyl butyral](https://bliptext.com/articles/polyvinyl-butyral).\nAn 8% solution of phosphoric acid in solvent was added just before application.\nIt was found that an easily oxidized alcohol was an essential ingredient.\nA thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured.\nThere is still a question as to the correct mechanism.\nChrome green is a mixture of [Prussian blue](https://bliptext.com/articles/prussian-blue) and [chrome yellow](https://bliptext.com/articles/chrome-yellow), while the chrome oxide green is [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium oxides are also used as a green pigment in the field of glassmaking and also as a glaze for ceramics.\nGreen chromium oxide is extremely [lightfast](https://bliptext.com/articles/lightfastness) and as such is used in cladding coatings.\nIt is also the main ingredient in [infrared](https://bliptext.com/articles/infrared) reflecting paints, used by the armed forces to paint vehicles and to give them the same [infrared](https://bliptext.com/articles/infrared) reflectance as green leaves.\n\n## Other uses\nChromium(III) ions present in [corundum](https://bliptext.com/articles/corundum) crystals (aluminium oxide) cause them to be colored red; when [corundum](https://bliptext.com/articles/corundum) appears as such, it is known as a [ruby](https://bliptext.com/articles/ruby).\nIf the corundum is lacking in chromium(III) ions, it is known as a [sapphire](https://bliptext.com/articles/sapphire).\nA red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies.\nSuch a synthetic ruby crystal was the basis for the first [laser](https://bliptext.com/articles/laser), produced in 1960, which relied on [stimulated emission](https://bliptext.com/articles/stimulated-emission) of light from the chromium atoms in such a crystal.\nRuby has a laser transition at 694.3 nanometers, in a deep red color.\nChromium(VI) salts are used for the preservation of wood.\nFor example, [chromated copper arsenate](https://bliptext.com/articles/chromated-copper-arsenate) (CCA) is used in [timber treatment](https://bliptext.com/articles/timber-treatment) to protect wood from decay fungi, wood-attacking insects, including [termites](https://bliptext.com/articles/termites), and marine borers.\nThe formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%.\nIn the United States, 65,300 metric tons of CCA solution were used in 1996.\nChromium(III) salts, especially [chrome alum](https://bliptext.com/articles/chrome-alum) and [chromium(III) sulfate](https://bliptext.com/articles/chromium-iii-sulfate), are used in the tanning of [leather](https://bliptext.com/articles/leather).\nThe chromium(III) stabilizes the leather by cross linking the [collagen](https://bliptext.com/articles/collagen) fibers.\nChromium tanned leather can contain 4–5% of chromium, which is tightly bound to the proteins.\nAlthough the form of chromium used for tanning is not the toxic hexavalent variety, there remains interest in management of chromium in the tanning industry.\nRecovery and reuse, direct/indirect recycling, and \"chrome-less\" or \"chrome-free\" tanning are practiced to better manage chromium usage.\nThe high heat resistivity and high melting point makes [chromite](https://bliptext.com/articles/chromite) and chromium(III) oxide a material for high temperature refractory applications, like [blast furnaces](https://bliptext.com/articles/blast-furnace), cement [kilns](https://bliptext.com/articles/kiln), molds for the firing of [bricks](https://bliptext.com/articles/brick) and as foundry sands for the [casting](https://bliptext.com/articles/casting-metalworking) of metals.\nIn these applications, the refractory materials are made from mixtures of chromite and magnesite.\nThe use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).\nSeveral chromium compounds are used as [catalysts](https://bliptext.com/articles/catalyst) for processing hydrocarbons.\nFor example, the [Phillips catalyst](https://bliptext.com/articles/phillips-catalyst), prepared from chromium oxides, is used for the production of about half the world's [polyethylene](https://bliptext.com/articles/polyethylene).\nFe-Cr mixed oxides are employed as high-temperature catalysts for the [water gas shift reaction](https://bliptext.com/articles/water-gas-shift-reaction).\n[Copper chromite](https://bliptext.com/articles/copper-chromite) is a useful [hydrogenation](https://bliptext.com/articles/hydrogenation) catalyst.\n# [Red crystal of a ruby laser | upload.wikimedia.org/wikipedia/commons/7/7d/5///Maiman///Laser///Components.jpg]\n\n## Uses of compounds\n\n# Biological role\nThe possible nutritional value of chromium(III) is unproven.\nAlthough chromium is regarded as a trace element and [dietary mineral](https://bliptext.com/articles/mineral-nutrient), its suspected roles in the action of [insulin](https://bliptext.com/articles/insulin) – a hormone that mediates the metabolism and storage of carbohydrate, fat, and protein – have not been adequately established.\nThe [mechanism of its actions](https://bliptext.com/articles/mechanism-of-action) in the body is undefined, leaving in doubt whether chromium has a biological role in healthy people.\nIn contrast, [hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium) (Cr(VI) or Cr6+) is highly toxic and [mutagenic](https://bliptext.com/articles/mutagen).\nIngestion of chromium(VI) in water has been linked to stomach tumors, and it may also cause allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis).\n\"[Chromium deficiency](https://bliptext.com/articles/chromium-deficiency)\", involving a lack of Cr(III) in the body, or perhaps some complex of it, such as [glucose tolerance factor](https://bliptext.com/articles/glucose-tolerance-factor), is not accepted as a medical condition, as it has no symptoms and healthy people do not require chromium supplementation.\nSome studies suggest that the biologically active form of chromium(III) is transported in the body via an oligopeptide called [low-molecular-weight chromium-binding substance](https://bliptext.com/articles/low-molecular-weight-chromium-binding-substance) (chromodulin), which might play a role in the insulin signaling pathway.\nThe chromium content of common foods is generally low (1–13 micrograms per serving).\nThe chromium content of food varies widely, due to differences in soil mineral content, growing season, plant [cultivar](https://bliptext.com/articles/cultivar), and contamination during processing.\nChromium (and [nickel](https://bliptext.com/articles/nickel)) leach into food cooked in stainless steel, with the effect being largest when the cookware is new.\nAcidic foods that are cooked for many hours also exacerbate this effect.\n\n## Dietary recommendations\nThere is disagreement on chromium's status as an essential nutrient.\nGovernmental departments from Australia, New Zealand, India, and Japan consider chromium as essential, while the United States and European Food Safety Authority of the European Union do not.\nThe U.S. [National Academy of Medicine](https://bliptext.com/articles/national-academy-of-medicine) (NAM) updated the [Estimated Average Requirements](https://bliptext.com/articles/dietary-reference-intake) (EARs) and the [Recommended Dietary Allowances](https://bliptext.com/articles/dietary-reference-intake) (RDAs) for chromium in 2001.\nFor chromium, there was insufficient information to set EARs and RDAs, so its needs are described as estimates for [Adequate Intake](https://bliptext.com/articles/dietary-reference-intake) (AI).\nFrom a 2001 assessment, AI of chromium for women ages 14 through 50 is 25 μg/day, and the AI for women ages 50 and above is 20 μg/day.\nThe AIs for women who are pregnant are 30 μg/day, and for women who are lactating, the set AI is 45 μg/day.\nThe AI for men ages 14 through 50 is 35 μg/day, and the AI for men ages 50 and above is 30 μg/day.\nFor children ages 1 through 13, the AI increases with age from 0.2 μg/day up to 25 μg/day.\nAs for safety, the NAM sets [Tolerable Upper Intake Levels](https://bliptext.com/articles/dietary-reference-intake) (ULs) for vitamins and minerals when the evidence is sufficient.\nIn the case of chromium, there is not yet enough information, hence no UL has been established.\nCollectively, the EARs, RDAs, AIs, and ULs are the parameters for the nutrition recommendation system known as [Dietary Reference Intake](https://bliptext.com/articles/dietary-reference-intake) (DRI).\nAustralia and New Zealand consider chromium to be an essential nutrient, with an AI of 35 μg/day for men, 25 μg/day for women, 30 μg/day for women who are pregnant, and 45 μg/day for women who are lactating.\nA UL has not been set due to the lack of sufficient data.\nIndia considers chromium to be an essential nutrient, with an adult recommended intake of 33 μg/day.\nJapan also considers chromium to be an essential nutrient, with an AI of 10 μg/day for adults, including women who are pregnant or lactating.\nA UL has not been set.\nThe EFSA does not consider chromium to be an essential nutrient.\n\n### Labeling\nFor U.S. food and dietary supplement labeling purposes, the amount of the substance in a serving is expressed as a percent of the [Daily Value](https://bliptext.com/articles/reference-daily-intake) (%DV).\nFor chromium labeling purposes, 100% of the Daily Value was 120 μg. As of 27 May 2016, the percentage of daily value was revised to 35 μg to bring the chromium intake into a consensus with the official [Recommended Dietary Allowance](https://bliptext.com/articles/dietary-reference-intake).\nA table of the old and new adult daily values in the United States is provided at [Reference Daily Intake](https://bliptext.com/articles/reference-daily-intake).\nAfter evaluation of research on the potential nutritional value of chromium, the European Food Safety Authority concluded that there was no evidence of benefit by dietary chromium in healthy people, thereby declining to establish recommendations in Europe for dietary intake of chromium.\n\n## Food sources\nFood composition databases such as those maintained by the U.S. Department of Agriculture do not contain information on the chromium content of foods.\nA wide variety of animal and vegetable foods contain chromium.\nContent per serving is influenced by the chromium content of the soil in which the plants are grown, by foodstuffs fed to animals, and by processing methods, as chromium is leached into foods if processed or cooked in stainless steel equipment.\nOne diet analysis study conducted in Mexico reported an average daily chromium intake of 30 micrograms.\nAn estimated 31% of adults in the United States consume multi-vitamin/mineral dietary supplements, which often contain 25 to 60 micrograms of chromium.\n\n## Supplementation\nChromium is an ingredient in [total parenteral nutrition](https://bliptext.com/articles/total-parenteral-nutrition) (TPN), because deficiency can occur after months of intravenous feeding with chromium-free TPN.\nIt is also added to nutritional products for [preterm infants](https://bliptext.com/articles/preterm-infant).\nAlthough the mechanism of action in biological roles for chromium is unclear, in the United States chromium-containing products are sold as non-prescription dietary supplements in amounts ranging from 50 to 1,000 μg. Lower amounts of chromium are also often incorporated into multi-vitamin/mineral supplements consumed by an estimated 31% of adults in the United States.\nChemical compounds used in dietary supplements include chromium chloride, chromium citrate, [chromium(III) picolinate](https://bliptext.com/articles/chromium-iii-picolinate), [chromium(III) polynicotinate](https://bliptext.com/articles/chromium-polynicotinate), and other chemical compositions.\nThe benefit of supplements has not been proven.\n\n### Initiation of research on glucose\nThe notion of chromium as a potential regulator of glucose metabolism began in the 1950s when scientists performed a series of experiments controlling the diet of rats.\nThe experimenters subjected the rats to a chromium deficient diet, and witnessed an inability to respond effectively to increased levels of blood glucose.\nA chromium-rich [Brewer's yeast](https://bliptext.com/articles/yeast) was provided in the diet, enabling the rats to effectively metabolize glucose, and so giving evidence that chromium may have a role in glucose management.\n\n## Approved and disapproved health claims\nIn 2005, the U.S. Food and Drug Administration had approved a qualified health claim for chromium picolinate with a requirement for specific label wording:\nIn other parts of the petition, the FDA rejected claims for chromium picolinate and cardiovascular disease, retinopathy or kidney disease caused by abnormally high blood sugar levels.\nAs of March 2024, this ruling on chromium remains in effect.\nIn 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements.\nApproved labeling statements include: a factor in the maintenance of good health, provides support for healthy glucose metabolism, helps the body to metabolize carbohydrates and helps the body to metabolize fats.\nThe European Food Safety Authority approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration, but rejected claims for maintenance or achievement of a normal body weight, or reduction of tiredness or fatigue.\nHowever, in a 2014 reassessment of studies to determine whether a Dietary Reference Intake value could be established for chromium, EFSA stated:\n\n### Diabetes\nGiven the evidence for chromium deficiency causing problems with glucose management in the context of intravenous nutrition products formulated without chromium, research interest turned to whether chromium supplementation would benefit people who have type 2 diabetes but are not chromium deficient.\nLooking at the results from four meta-analyses, one reported a statistically significant decrease in fasting [plasma glucose](https://bliptext.com/articles/plasma-glucose) levels and a non-significant trend in lower [hemoglobin A1C](https://bliptext.com/articles/glycated-hemoglobin).\nA second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either.\nA review published in 2016 listed 53 [randomized clinical trials](https://bliptext.com/articles/randomized-clinical-trial) that were included in one or more of six [meta-analyses](https://bliptext.com/articles/meta-analysis).\nIt concluded that whereas there may be modest decreases in fasting blood glucose and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome.\n\n### Body weight\nTwo [systematic reviews](https://bliptext.com/articles/systematic-review) looked at chromium supplements as a mean of managing body weight in overweight and obese people.\nOne, limited to [chromium picolinate](https://bliptext.com/articles/chromium-picolinate), a common supplement ingredient, reported a statistically significant −1.1 kg (2.4 lb) weight loss in trials longer than 12 weeks.\nThe other included all chromium compounds and reported a statistically significant −0.50 kg (1.1 lb) weight change.\nChange in percent body fat did not reach statistical significance.\nAuthors of both reviews considered the clinical relevance of this modest weight loss as uncertain/unreliable.\nThe European Food Safety Authority reviewed the literature and concluded that there was insufficient evidence to support a claim.\n\n### Sports\nChromium is promoted as a sports performance dietary supplement, based on the theory that it potentiates insulin activity, with anticipated results of increased muscle mass, and faster recovery of glycogen storage during post-exercise recovery.\nA review of clinical trials reported that chromium supplementation did not improve exercise performance or increase muscle strength.\nThe International Olympic Committee reviewed dietary supplements for high-performance athletes in 2018 and concluded there was no need to increase chromium intake for athletes, nor support for claims of losing body fat.\n\n## Fresh-water fish\nIrrigation water standards for chromium are 0.1 mg/L, but some rivers in [Bangladesh](https://bliptext.com/articles/bangladesh) are more than five times that amount.\nThe standard for fish for human consumption is less than 1 mg/kg, but many tested samples were more than five times that amount.\nChromium, especially hexavalent chromium, is highly toxic to fish because it is easily absorbed across the gills, readily enters blood circulation, crosses cell membranes and bioconcentrates up the food chain.\nIn contrast, the toxicity of trivalent chromium is very low, attributed to poor membrane permeability and little biomagnification.\nAcute and chronic exposure to chromium(VI) affects fish behavior, physiology, reproduction and survival.\nHyperactivity and erratic swimming have been reported in contaminated environments.\nEgg hatching and fingerling survival are affected.\nIn adult fish there are reports of histopathological damage to liver, kidney, muscle, intestines, and gills.\nMechanisms include mutagenic gene damage and disruptions of enzyme functions.\nThere is evidence that fish may not require chromium, but benefit from a measured amount in diet.\nIn one study, juvenile fish gained weight on a zero chromium diet, but the addition of 500 μg of chromium in the form of chromium chloride or other supplement types, per kilogram of food (dry weight), increased weight gain.\nAt 2,000 μg/kg the weight gain was no better than with the zero chromium diet, and there were increased DNA strand breaks.\n\n# Precautions\nWater-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.\nBecause of the specific [transport](https://bliptext.com/articles/transport-protein) mechanisms, only limited amounts of chromium(III) enter the cells.\nAcute oral toxicity ranges between 50 and 150 mg/kg.\nA 2008 review suggested that moderate uptake of chromium(III) through dietary supplements poses no genetic-toxic risk.\nIn the US, the [Occupational Safety and Health Administration](https://bliptext.com/articles/occupational-safety-and-health-administration) (OSHA) has designated an air [permissible exposure limit](https://bliptext.com/articles/permissible-exposure-limit) (PEL) in the workplace as a time-weighted average (TWA) of 1 mg/m3.\nThe [National Institute for Occupational Safety and Health](https://bliptext.com/articles/national-institute-for-occupational-safety-and-health) (NIOSH) has set a [recommended exposure limit](https://bliptext.com/articles/recommended-exposure-limit) (REL) of 0.5 mg/m3, time-weighted average.\nThe [IDLH](https://bliptext.com/articles/idlh) (immediately dangerous to life and health) value is 250 mg/m3.\n\n## Chromium(VI) toxicity\nThe acute [oral](https://bliptext.com/articles/mouth) [toxicity](https://bliptext.com/articles/toxicity) for [chromium(VI)](https://bliptext.com/articles/hexavalent-chromium) ranges between 1.5 and 3.3 mg/kg.\nIn the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells.\nThe chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also [sulfate](https://bliptext.com/articles/sulfate) and [phosphate](https://bliptext.com/articles/phosphate) ions enter the cell.\nThe acute toxicity of chromium(VI) is due to its strong [oxidant](https://bliptext.com/articles/redox) properties.\nAfter it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions.\n[Hemolysis](https://bliptext.com/articles/hemolysis), [renal](https://bliptext.com/articles/renal), and liver failure result.\nAggressive dialysis can be therapeutic.\nThe [carcinogenity](https://bliptext.com/articles/carcinogenity) of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.\nThree mechanisms have been proposed to describe the [genotoxicity](https://bliptext.com/articles/genotoxicity) of chromium(VI).\nThe first mechanism includes highly reactive [hydroxyl radicals](https://bliptext.com/articles/hydroxyl-radical) and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III).\nThe second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the [DNA](https://bliptext.com/articles/dna).\nThe last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.\nChromium salts (chromates) are also the cause of [allergic reactions](https://bliptext.com/articles/allergic-reaction) in some people.\nChromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.\nContact with products containing chromates can lead to allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis) and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as \"chrome ulcers\".\nThis condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.\n\n## Environmental issues\nBecause chromium compounds were used in [dyes](https://bliptext.com/articles/dye), [paints](https://bliptext.com/articles/paint), and [leather](https://bliptext.com/articles/leather) [tanning](https://bliptext.com/articles/tanning-leather) compounds, these compounds are often found in soil and [groundwater](https://bliptext.com/articles/groundwater) at active and abandoned industrial sites, needing [environmental cleanup](https://bliptext.com/articles/environmental-cleanup) and [remediation](https://bliptext.com/articles/environmental-remediation).\n[Primer paint](https://bliptext.com/articles/primer-paint) containing hexavalent chromium is still widely used for [aerospace](https://bliptext.com/articles/aerospace) and [automobile](https://bliptext.com/articles/automobile) refinishing applications.\nIn 2010, the [Environmental Working Group](https://bliptext.com/articles/environmental-working-group) studied the drinking water in 35 American cities in the first nationwide study.\nThe study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with [Norman, Oklahoma](https://bliptext.com/articles/norman-oklahoma), at the top of list; 25 cities had levels that exceeded California's proposed limit.\nThe more toxic hexavalent chromium form can be reduced to the less soluble trivalent oxidation state in soils by organic matter, ferrous iron, sulfides, and other reducing agents, with the rates of such reduction being faster under more acidic conditions than under more alkaline ones.\nIn contrast, trivalent chromium can be oxidized to hexavalent chromium in soils by manganese oxides, such as Mn(III) and Mn(IV) compounds.\nSince the solubility and toxicity of chromium (VI) are greater that those of chromium (III), the oxidation-reduction conversions between the two oxidation states have implications for movement and bioavailability of chromium in soils, groundwater, and plants.\n\n# General bibliography","wordIndex":784,"createdAt":"2025-03-18T15:13:42.318Z","user":{"id":"jr9320kzLD37CkxadNfMG9YBINNdhTeS","name":"The Raters","image":"https://lh3.googleusercontent.com/a/ACg8ocIdQIQQjHI233tCJ_h-vtFv9t351nMGaL3Sfolwv8P7mLg2Ez0=s96-c"}}],"article":{"id":"c586ebee-801a-44b6-a0ce-9d4ff8927a78","title":"Chromium","slug":"chromium","content":":::summary\n**Vickers Hardness:** 950HV \n**Vickers Hardness Ref:** https://www.journalmt.com/pdfs/mft/2018/04/16.pdf \n:::\n\n# \n**Chromium** is a [chemical element](https://bliptext.com/articles/chemical-element); it has [symbol](https://bliptext.com/articles/symbol-chemistry) **Cr** and [atomic number](https://bliptext.com/articles/atomic-number) 24.\nIt is the first element in [group 6](https://bliptext.com/articles/group-6-element).\nIt is a steely-grey, [lustrous](https://bliptext.com/articles/luster-mineralogy), hard, and brittle [transition metal](https://bliptext.com/articles/transition-metal).\nChromium is valued for its high [corrosion](https://bliptext.com/articles/corrosion) resistance and [hardness](https://bliptext.com/articles/hardness).\nA major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form [stainless steel](https://bliptext.com/articles/stainless-steel).\nStainless steel and [chrome plating](https://bliptext.com/articles/chrome-plating) ([electroplating](https://bliptext.com/articles/electroplating) with chromium) together comprise 85% of the commercial use.\nChromium is also greatly valued as a [metal](https://bliptext.com/articles/metal) that is able to be highly [polished](https://bliptext.com/articles/polishing) while resisting [tarnishing](https://bliptext.com/articles/tarnish).\nPolished chromium reflects almost 70% of the [visible spectrum](https://bliptext.com/articles/visible-spectrum), and almost 90% of [infrared light](https://bliptext.com/articles/infrared).\nThe name of the element is derived from the [Greek](https://bliptext.com/articles/ancient-greek) word χρῶμα, chrōma, meaning [color](https://bliptext.com/articles/color), because many chromium compounds are intensely [color](https://bliptext.com/articles/color)ed.\nIndustrial production of chromium proceeds from [chromite](https://bliptext.com/articles/chromite) ore (mostly FeCr2O4) to produce [ferrochromium](https://bliptext.com/articles/ferrochromium), an iron-chromium alloy, by means of [aluminothermic](https://bliptext.com/articles/aluminothermic-reaction) or [silicothermic reactions](https://bliptext.com/articles/silicothermic-reaction).\nFerrochromium is then used to produce alloys such as stainless steel.\nPure chromium metal is produced by a different process: [roasting](https://bliptext.com/articles/roasting-metallurgy) and [leaching](https://bliptext.com/articles/leaching-metallurgy) of chromite to separate it from iron, followed by reduction with [carbon](https://bliptext.com/articles/carbon) and then [aluminium](https://bliptext.com/articles/aluminium).\n[Trivalent](https://bliptext.com/articles/trivalent) chromium (Cr(III)) occurs naturally in many foods and is sold as a [dietary supplement](https://bliptext.com/articles/dietary-supplement), although there is insufficient evidence that dietary chromium provides nutritional benefit to people.\nIn 2014, the [European Food Safety Authority](https://bliptext.com/articles/european-food-safety-authority) concluded that research on dietary chromium did not justify it to be recognized as an essential [nutrient](https://bliptext.com/articles/nutrient).\nWhile chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called \"[hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium)\", is toxic and [carcinogenic](https://bliptext.com/articles/carcinogenic).\nAccording to the European Chemicals Agency (ECHA), [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) that is used in industrial electroplating processes is a \"substance of very high concern\" (SVHC).\n\n# Physical properties\n\n## Atomic\nGaseous chromium has a ground-state [electron configuration](https://bliptext.com/articles/electron-configuration) of [ [Ar](https://bliptext.com/articles/argon)] 3d5 4s1.\nIt is the first element in the periodic table whose configuration violates the [Aufbau principle](https://bliptext.com/articles/aufbau-principle).\nExceptions to the principle also occur later in the periodic table for elements such as [copper](https://bliptext.com/articles/copper), [niobium](https://bliptext.com/articles/niobium) and [molybdenum](https://bliptext.com/articles/molybdenum).\nChromium is the first element in the 3d series where the 3d electrons start to sink into the core; they thus contribute less to [metallic bonding](https://bliptext.com/articles/metallic-bonding), and hence the melting and boiling points and the [enthalpy of atomisation](https://bliptext.com/articles/enthalpy-of-atomisation) of chromium are lower than those of the preceding element [vanadium](https://bliptext.com/articles/vanadium).\nChromium(VI) is a strong [oxidising agent](https://bliptext.com/articles/oxidising-agent) in contrast to the [molybdenum](https://bliptext.com/articles/molybdenum)(VI) and [tungsten](https://bliptext.com/articles/tungsten)(VI) oxides.\n\n## Bulk\nChromium is the third hardest element after [carbon](https://bliptext.com/articles/carbon) ([diamond](https://bliptext.com/articles/diamond)) and [boron](https://bliptext.com/articles/boron).\nIts [Mohs hardness](https://bliptext.com/articles/mohs-scale-of-mineral-hardness) is 8.5, which means that it can scratch samples of [quartz](https://bliptext.com/articles/quartz) and [topaz](https://bliptext.com/articles/topaz), but can be scratched by [corundum](https://bliptext.com/articles/corundum).\nChromium is highly resistant to [tarnishing](https://bliptext.com/articles/tarnish), which makes it useful as a metal that preserves its outermost layer from [corroding](https://bliptext.com/articles/corrosion), unlike other metals such as [copper](https://bliptext.com/articles/copper), [magnesium](https://bliptext.com/articles/magnesium), and [aluminium](https://bliptext.com/articles/aluminium).\nChromium has a [melting point](https://bliptext.com/articles/melting-point) of 1907 °C (3465 °F), which is relatively low compared to the majority of transition metals.\nHowever, it still has the second highest melting point out of all the [period 4 elements](https://bliptext.com/articles/period-4-element), being topped by [vanadium](https://bliptext.com/articles/vanadium) by 3 °C (5 °F) at 1910 °C (3470 °F).\nThe [boiling point](https://bliptext.com/articles/boiling-point) of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest [boiling point](https://bliptext.com/articles/boiling-point) out of the [Period 4](https://bliptext.com/articles/period-4) [transition metals](https://bliptext.com/articles/transition-metal) alone behind [copper](https://bliptext.com/articles/copper), [manganese](https://bliptext.com/articles/manganese) and [zinc](https://bliptext.com/articles/zinc).\nThe [electrical resistivity](https://bliptext.com/articles/electrical-resistivity-and-conductivity) of chromium at 20 °C is 125 [nanoohm](https://bliptext.com/articles/ohm)-[meters](https://bliptext.com/articles/meter).\nChromium has a high [specular reflection](https://bliptext.com/articles/specular-reflection) in comparison to other transition metals.\nIn [infrared](https://bliptext.com/articles/infrared), at 425 [μm](https://bliptext.com/articles/micrometre), chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 [μm](https://bliptext.com/articles/micrometre) before rising again to 90% at 4000 [μm](https://bliptext.com/articles/micrometre).\nWhen chromium is used in [stainless steel](https://bliptext.com/articles/stainless-steel) alloys and [polished](https://bliptext.com/articles/polishing), the specular reflection decreases with the inclusion of additional metals, yet is still high in comparison with other alloys.\nBetween 40% and 60% of the visible spectrum is reflected from polished stainless steel.\nThe explanation on why chromium displays such a high turnout of reflected [photon](https://bliptext.com/articles/photon) waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties.\nChromium has unique magnetic properties; it is the only elemental solid that shows [antiferromagnetic](https://bliptext.com/articles/antiferromagnetic) ordering at room temperature and below.\nAbove 38 °C, its magnetic ordering becomes [paramagnetic](https://bliptext.com/articles/paramagnetic).\nThe antiferromagnetic properties, which cause the chromium atoms to temporarily [ionize](https://bliptext.com/articles/ionization) and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the [lattice periodicity](https://bliptext.com/articles/crystal-structure).\nThis is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers.\nFrom here, the frequency-dependent [relative permittivity](https://bliptext.com/articles/relative-permittivity) of chromium, deriving from [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations) and Chromakopia By, Tylerthecreator chromium with a high infrared and visible light reflectance.\n# [Sample of chromium metal | upload.wikimedia.org/wikipedia/commons/a/a1/Chromium.jpg]\n\n### Passivation\nChromium metal in air is [passivated](https://bliptext.com/articles/passivation-chemistry): it forms a thin, protective surface layer of chromium oxide with the [corundum](https://bliptext.com/articles/corundum-structure) structure.\nPassivation can be enhanced by short contact with [oxidizing acids](https://bliptext.com/articles/oxidizing-acid) like [nitric acid](https://bliptext.com/articles/nitric-acid).\nPassivated chromium is stable against acids.\nPassivation can be removed with a strong [reducing agent](https://bliptext.com/articles/reducing-agent) that destroys the protective oxide layer on the metal.\nChromium metal treated in this way readily dissolves in weak acids.\nThe surface [chromia](https://bliptext.com/articles/chromium-iii-oxide) Cr2O3 scale, is adherent to the metal.\nIn contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued [rusting](https://bliptext.com/articles/rust).\nAt room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward [diffusion](https://bliptext.com/articles/atomic-diffusion) of metal ions across the scale.\nAbove 950 °C volatile [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) CrO3 forms from the chromia scale, limiting the scale thickness and oxidation protection.\nChromium, unlike iron and nickel, does not suffer from [hydrogen embrittlement](https://bliptext.com/articles/hydrogen-embrittlement).\nHowever, it does suffer from nitrogen [embrittlement](https://bliptext.com/articles/embrittlement), reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.\n\n## Isotopes\nNaturally occurring chromium is composed of four stable [isotopes](https://bliptext.com/articles/isotope); 50Cr, 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% [natural abundance](https://bliptext.com/articles/natural-abundance)).\n50Cr is [observationally stable](https://bliptext.com/articles/stable-nuclide), as it is theoretically capable of [decaying](https://bliptext.com/articles/radioactive-decay) to [50Ti](https://bliptext.com/articles/isotopes-of-titanium) via [double electron capture](https://bliptext.com/articles/double-electron-capture) with a [half-life](https://bliptext.com/articles/half-life) of no less than 1.3 years.\nTwenty-five [radioisotopes](https://bliptext.com/articles/radioisotope) have been characterized, ranging from 42Cr to 70Cr; the most stable radioisotope is 51Cr with a half-life of 27.7 days.\nAll of the remaining [radioactive](https://bliptext.com/articles/radioactive) isotopes have half-lives that are less than 24 hours and the majority less than 1 minute.\nChromium also has two [metastable](https://bliptext.com/articles/metastable) [nuclear isomers](https://bliptext.com/articles/nuclear-isomer).\nThe primary [decay mode](https://bliptext.com/articles/decay-mode) before the most abundant stable isotope, 52Cr, is [electron capture](https://bliptext.com/articles/electron-capture) and the primary mode after is [beta decay](https://bliptext.com/articles/beta-decay).\n53Cr is the [radiogenic](https://bliptext.com/articles/radiogenic) decay product of 53[Mn](https://bliptext.com/articles/manganese) (half-life 3.74 million years).\nChromium isotopes are typically collocated (and compounded) with [manganese](https://bliptext.com/articles/manganese) isotopes.\nThis circumstance is useful in [isotope geology](https://bliptext.com/articles/isotope-geology).\nManganese-chromium isotope ratios reinforce the evidence from [26Al](https://bliptext.com/articles/aluminium-26) and 107[Pd](https://bliptext.com/articles/palladium) concerning the early history of the [Solar System](https://bliptext.com/articles/solar-system).\nVariations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies.\nHence 53Cr provides additional evidence for [nucleosynthetic](https://bliptext.com/articles/nucleosynthesis) processes immediately before coalescence of the Solar System.\n53Cr has been posited as a proxy for atmospheric oxygen concentration.\n\n# Chemistry and compounds\nChromium is a member of [group 6](https://bliptext.com/articles/group-6-element), of the [transition metals](https://bliptext.com/articles/transition-metal).\nThe +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.\n# [The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide | upload.wikimedia.org/wikipedia/commons/c/c3/Chromium///in///water///pourbiax///diagram.png]\n\n## Common oxidation states\n\n### Chromium(0)\nMany Cr(0) complexes are known.\n[Bis(benzene)chromium](https://bliptext.com/articles/bis-benzene-chromium) and [chromium hexacarbonyl](https://bliptext.com/articles/chromium-hexacarbonyl) are highlights in [organochromium chemistry](https://bliptext.com/articles/organochromium-chemistry).\n\n### Chromium(II)\nChromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air.\nWater-stable [chromium(II) chloride](https://bliptext.com/articles/chromium-ii-chloride) that can be made by reducing chromium(III) chloride with zinc.\nThe resulting bright blue solution created from dissolving chromium(II) chloride is stable at neutral [pH](https://bliptext.com/articles/ph).\nSome other notable chromium(II) compounds include [chromium(II) oxide](https://bliptext.com/articles/chromium-ii-oxide), and [chromium(II) sulfate](https://bliptext.com/articles/chromium-ii-sulfate).\nMany chromium(II) carboxylates are known.\nThe red [chromium(II) acetate](https://bliptext.com/articles/chromium-ii-acetate) (Cr2(O2CCH3)4) is somewhat famous.\nIt features a Cr-Cr [quadruple bond](https://bliptext.com/articles/quadruple-bond).\n# [Chromium(II) carbide (Cr3C2) | upload.wikimedia.org/wikipedia/commons/e/eb/Chromium///carbide///Cr3C2.JPG]\n\n### Chromium(III)\nA large number of chromium(III) compounds are known, such as [chromium(III) nitrate](https://bliptext.com/articles/chromium-nitrate), [chromium(III) acetate](https://bliptext.com/articles/chromium-iii-acetate), and [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium(III) can be obtained by dissolving elemental chromium in acids like [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid) or [sulfuric acid](https://bliptext.com/articles/sulfuric-acid), but it can also be formed through the reduction of chromium(VI) by [cytochrome](https://bliptext.com/articles/cytochrome) [c7](https://bliptext.com/articles/cytochrome-c).\nThe ion has a similar radius (63 [pm](https://bliptext.com/articles/picometer)) to (radius 50 [pm](https://bliptext.com/articles/picometer)), and they can replace each other in some compounds, such as in [chrome alum](https://bliptext.com/articles/chrome-[alum](https://bliptext.com/articles/alum)) and [alum](https://bliptext.com/articles/alum).\nChromium(III) tends to form [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) complexes.\nCommercially available [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) hydrate is the dark green complex [CrCl2(H2O)4]Cl.\nClosely related compounds are the pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.\nIf anhydrous violet [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) is dissolved in water, the violet solution turns green after some time as the chloride in the inner [coordination sphere](https://bliptext.com/articles/coordination-sphere) is replaced by water.\nThis kind of reaction is also observed with solutions of [chrome alum](https://bliptext.com/articles/chrome-alum) and other water-soluble chromium(III) salts.\nA [tetrahedral](https://bliptext.com/articles/tetrahedral-molecular-geometry) coordination of [chromium(III)](https://bliptext.com/articles/chromium-iii) has been reported for the Cr-centered [Keggin](https://bliptext.com/articles/keggin-structure) anion [α-CrW12O40]5–.\n[Chromium(III) hydroxide](https://bliptext.com/articles/chromium-iii-hydroxide) (Cr(OH)3) is [amphoteric](https://bliptext.com/articles/amphoterism), dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form.\nIt is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), a stable oxide with a crystal structure identical to that of [corundum](https://bliptext.com/articles/corundum).\n# [Anhydrous chromium(III) chloride (CrCl3) | upload.wikimedia.org/wikipedia/commons/3/3b/Chromium%28III%29-chloride-purple-anhydrous-sunlight.jpg]\n\n### Chromium(VI)\n[Chromium(VI) compounds](https://bliptext.com/articles/hexavalent-chromium) are oxidants at low or neutral pH.\n[Chromate](https://bliptext.com/articles/chromate-and-[dichromate](https://bliptext.com/articles/chromate-and-dichromate)) anions and [dichromate](https://bliptext.com/articles/chromate-and-dichromate) (Cr2O72−) anions are the principal ions at this oxidation state.\nThey exist at an equilibrium, determined by pH:\nChromium(VI) oxyhalides are known also and include [chromyl fluoride](https://bliptext.com/articles/chromyl-fluoride) (CrO2F2) and [chromyl chloride](https://bliptext.com/articles/chromyl-chloride).\nHowever, despite several erroneous claims, [chromium hexafluoride](https://bliptext.com/articles/chromium-hexafluoride) (as well as all higher hexahalides) remains unknown, as of 2020.\n[Sodium chromate](https://bliptext.com/articles/sodium-chromate) is produced industrially by the oxidative roasting of [chromite](https://bliptext.com/articles/chromite) ore with [sodium carbonate](https://bliptext.com/articles/sodium-carbonate).\nThe change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of [potassium chromate](https://bliptext.com/articles/potassium-chromate).\nAt yet lower pH values, further condensation to more complex [oxyanions](https://bliptext.com/articles/oxyanion) of chromium is possible.\nBoth the [chromate and dichromate](https://bliptext.com/articles/chromate-and-dichromate) anions are strong oxidizing reagents at low pH:\nThey are, however, only moderately oxidizing at high pH:\nChromium(VI) compounds in solution can be detected by adding an acidic [hydrogen peroxide](https://bliptext.com/articles/hydrogen-peroxide) solution.\nThe unstable dark blue [chromium(VI) peroxide](https://bliptext.com/articles/chromium-vi-peroxide) (CrO5) is formed, which can be stabilized as an ether adduct.\n[Chromic acid](https://bliptext.com/articles/chromic-acid) has the hypothetical formula.\nIt is a vaguely described chemical, despite many well-defined chromates and dichromates being known.\nThe dark red [chromium(VI) oxide](https://bliptext.com/articles/chromium-vi-oxide), the acid [anhydride](https://bliptext.com/articles/anhydride) of chromic acid, is sold industrially as \"chromic acid\".\nIt can be produced by mixing sulfuric acid with dichromate and is a strong oxidizing agent.\n# [Chromium(VI) oxide | upload.wikimedia.org/wikipedia/commons/1/1e/Chrom%28VI%29-oxid.jpg]\n# [Sodium chromate (Na2CrO4) | upload.wikimedia.org/wikipedia/commons/5/51/Chroman///sodn%C3%BD.JPG]\n\n## Other oxidation states\nCompounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate.\nThe only binary compound is the volatile [chromium(V) fluoride](https://bliptext.com/articles/chromium-v-fluoride) (CrF5).\nThis red solid has a melting point of 30 °C and a boiling point of 117 °C.\nIt can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure.\nThe peroxochromate(V) is another example of the +5 oxidation state.\n[Potassium peroxochromate](https://bliptext.com/articles/potassium-tetraperoxochromate-v) (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures.\nThis red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.\nCompounds of chromium(IV) are slightly more common than those of chromium(V).\nThe tetrahalides, [CrF4](https://bliptext.com/articles/chromium-iv-fluoride), [CrCl4](https://bliptext.com/articles/chromium-iv-chloride), and CrBr4, can be produced by treating the trihalides with the corresponding halogen at elevated temperatures.\nSuch compounds are susceptible to disproportionation reactions and are not stable in water.\nOrganic compounds containing Cr(IV) state such as chromium tetra t-butoxide are also known.\nMost chromium(I) compounds are obtained solely by oxidation of electron-rich, [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) chromium(0) complexes.\nOther chromium(I) complexes contain [cyclopentadienyl](https://bliptext.com/articles/cyclopentadienyl) ligands.\nAs verified by [X-ray diffraction](https://bliptext.com/articles/x-ray-diffraction), a Cr-Cr [quintuple bond](https://bliptext.com/articles/quintuple-bond) (length 183.51(4) pm) has also been described.\nExtremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.\n# [Chromium compound determined experimentally to contain a Cr-Cr quintuple bond | upload.wikimedia.org/wikipedia/commons/6/60/5-fold///chromium.png]\n\n# Occurrence\nChromium is the 21st most [abundant element in Earth's crust](https://bliptext.com/articles/abundance-of-elements-in-earth-s-crust) with an average concentration of 100 ppm.\nChromium compounds are found in the environment from the [erosion](https://bliptext.com/articles/erosion) of chromium-containing rocks, and can be redistributed by volcanic eruptions.\nTypical background concentrations of chromium in environmental media are: atmosphere <10 ng/m3; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg.\nChromium is mined as chromite (FeCr2O4) ore.\nAbout two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers.\nUntapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.\nAlthough rare, deposits of [native](https://bliptext.com/articles/native-metal) chromium exist.\nThe [Udachnaya Pipe](https://bliptext.com/articles/udachnaya-pipe) in Russia produces samples of the native metal.\nThis mine is a [kimberlite](https://bliptext.com/articles/kimberlite) pipe, rich in [diamonds](https://bliptext.com/articles/diamond), and the [reducing environment](https://bliptext.com/articles/redox) helped produce both elemental chromium and [diamonds](https://bliptext.com/articles/diamond).\nThe relation between Cr(III) and Cr(VI) strongly depends on [pH](https://bliptext.com/articles/ph) and [oxidative](https://bliptext.com/articles/oxidative) properties of the location.\nIn most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L is Cr(VI).\n# [Crocoite (PbCrO4) | upload.wikimedia.org/wikipedia/commons/a/ac/Crocoite///from///Tasmania.jpg]\n# [Chromite ore | upload.wikimedia.org/wikipedia/commons/0/00/Chromit///1.jpg]\n\n# History\n\n## Early applications\nChromium minerals as pigments came to the attention of the west in the eighteenth century.\nOn 26 July 1761, [Johann Gottlob Lehmann](https://bliptext.com/articles/johann-gottlob-lehmann-scientist) found an orange-red mineral in the [Beryozovskoye mines](https://bliptext.com/articles/beryozovskoye-deposit) in the [Ural Mountains](https://bliptext.com/articles/ural-mountains) which he named Siberian red lead.\nThough misidentified as a [lead](https://bliptext.com/articles/lead) compound with [selenium](https://bliptext.com/articles/selenium) and [iron](https://bliptext.com/articles/iron) components, the mineral was in fact [crocoite](https://bliptext.com/articles/crocoite) with a formula of PbCrO4.\nIn 1770, [Peter Simon Pallas](https://bliptext.com/articles/peter-simon-pallas) visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a [pigment](https://bliptext.com/articles/pigment) in [paints](https://bliptext.com/articles/paint).\nAfter Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region.\nCrocoite would be the principal source of chromium in pigments until the discovery of [chromite](https://bliptext.com/articles/chromite) many years later.\nIn 1794, [Louis Nicolas Vauquelin](https://bliptext.com/articles/louis-nicolas-vauquelin) received samples of crocoite [ore](https://bliptext.com/articles/ore).\nHe produced [chromium trioxide](https://bliptext.com/articles/chromium-vi-oxide) (CrO3) by mixing crocoite with [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid).\nIn 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.\nVauquelin was also able to detect traces of chromium in precious [gemstones](https://bliptext.com/articles/gemstone), such as [ruby](https://bliptext.com/articles/ruby) and [emerald](https://bliptext.com/articles/emerald).\nDuring the nineteenth century, chromium was primarily used not only as a component of paints, but in [tanning](https://bliptext.com/articles/tanning-leather) salts as well.\nFor quite some time, the crocoite found in Russia was the main source for such tanning materials.\nIn 1827, a larger chromite deposit was discovered near [Baltimore](https://bliptext.com/articles/baltimore), United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.\nThis made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of [Bursa](https://bliptext.com/articles/bursa), Turkey.\nWith the development of metallurgy and chemical industries in the Western world, the need for chromium increased.\nChromium is also famous for its reflective, metallic luster when polished.\nIt is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by [electroplating](https://bliptext.com/articles/electroplating).\nChromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.\n# [The red color of rubies is due to trace amounts of chromium within the corundum. | upload.wikimedia.org/wikipedia/commons/c/c4/Cut///Ruby.jpg]\n\n# Production\nApproximately 28.8 million metric tons (Mt) of marketable chromite ore was produced in 2013, and converted into 7.5 Mt of ferrochromium.\nAccording to John F. Papp, writing for the USGS, \"Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium.\"\nThe largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing the rest of about 18% of the world production.\nThe two main products of chromium ore refining are [ferrochromium](https://bliptext.com/articles/ferrochromium) and metallic chromium.\nFor those products the ore smelter process differs considerably.\nFor the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in [electric arc furnace](https://bliptext.com/articles/electric-arc-furnace) or in smaller smelters with either [aluminium](https://bliptext.com/articles/aluminium) or [silicon](https://bliptext.com/articles/silicon) in an [aluminothermic reaction](https://bliptext.com/articles/aluminothermic-reaction).\nFor the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process.\nThe chromite ore is heated with a mixture of [calcium carbonate](https://bliptext.com/articles/calcium-carbonate) and [sodium carbonate](https://bliptext.com/articles/sodium-carbonate) in the presence of air.\nThe chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.\nThe subsequent leaching at higher elevated temperatures dissolves the [chromates](https://bliptext.com/articles/chromates) and leaves the insoluble iron oxide.\nThe chromate is converted by [sulfuric acid](https://bliptext.com/articles/sulfuric-acid) into the dichromate.\nThe dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.\n# [Piece of chromium produced with aluminothermic reaction | upload.wikimedia.org/wikipedia/commons/c/cf/Chrom///1.jpg]\n# [World production trend of chromium | upload.wikimedia.org/wikipedia/commons/5/5f/Chromium///-///world///production///trend.svg]\n# [Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains | upload.wikimedia.org/wikipedia/commons/4/42/Chromium///zone///refined///and///1cm3///cube.jpg]\n# [Chromium ore output in 2002 | upload.wikimedia.org/wikipedia/commons/2/2c/World///Chromium///Production///2002.svg]\n\n# Applications\nThe creation of metal alloys account for 85% of the available chromium's usage.\nThe remainder of chromium is used in the [chemical](https://bliptext.com/articles/chemical-industry), [refractory](https://bliptext.com/articles/refractory), and [foundry](https://bliptext.com/articles/foundry) industries.\n\n## Metallurgy\nThe strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.\n[High-speed tool steels](https://bliptext.com/articles/high-speed-steel) contain 3–5% chromium.\n[Stainless steel](https://bliptext.com/articles/stainless-steel), the primary corrosion-resistant metal alloy, is formed when chromium is introduced to [iron](https://bliptext.com/articles/iron) in concentrations above 11%.\nFor stainless steel's formation, ferrochromium is added to the molten iron.\nAlso, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries.\nFor example, [Inconel](https://bliptext.com/articles/inconel) 718 contains 18.6% chromium.\nBecause of the excellent high-temperature properties of these nickel [superalloys](https://bliptext.com/articles/superalloy), they are used in [jet engines](https://bliptext.com/articles/jet-engine) and [gas turbines](https://bliptext.com/articles/gas-turbine) in lieu of common structural materials.\n[ASTM](https://bliptext.com/articles/astm) B163 relies on chromium for condenser and heat-exchanger tubes, while [castings](https://bliptext.com/articles/castings) with high strength at elevated temperatures that contain chromium are standardised with [ASTM](https://bliptext.com/articles/astm) A567.\n[AISI](https://bliptext.com/articles/american-iron-and-steel-institute) type 332 is used where high temperature would normally cause [carburization](https://bliptext.com/articles/carburization), [oxidation](https://bliptext.com/articles/oxidation) or [corrosion](https://bliptext.com/articles/corrosion).\n[Incoloy](https://bliptext.com/articles/incoloy) 800 \"is capable of remaining stable and maintaining its [austenitic](https://bliptext.com/articles/austenitic) structure even after long time exposures to high temperatures\".\n[Nichrome](https://bliptext.com/articles/nichrome) is used as resistance wire for heating elements in things like [toasters](https://bliptext.com/articles/toasters) and space heaters.\nThese uses make chromium a [strategic material](https://bliptext.com/articles/strategic-material).\nConsequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it \"may become a critical material during the emergency\".\nThe United States likewise considered chromium \"essential for the German war industry\" and made intense diplomatic efforts to keep it out of the hands of [Nazi Germany](https://bliptext.com/articles/nazi-germany).\nThe high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals.\nA layer of chromium is deposited on pretreated metallic surfaces by [electroplating](https://bliptext.com/articles/electroplating) techniques.\nThere are two deposition methods: thin, and thick.\nThin deposition involves a layer of chromium below 1 μm thickness deposited by [chrome plating](https://bliptext.com/articles/chrome-plating), and is used for decorative surfaces.\nThicker chromium layers are deposited if wear-resistant surfaces are needed.\nBoth methods use acidic chromate or [dichromate](https://bliptext.com/articles/dichromate) solutions.\nTo prevent the energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used.\nIn the [chromate conversion coating](https://bliptext.com/articles/chromate-conversion-coating) process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium.\nThis [passivation](https://bliptext.com/articles/passivation-chemistry) and the self-healing properties of the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.\nBecause of environmental and health regulations on chromates, alternative coating methods are under development.\nChromic acid [anodizing](https://bliptext.com/articles/anodizing) (or Type I [anodizing](https://bliptext.com/articles/anodizing)) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses [chromic acid](https://bliptext.com/articles/chromic-acid) as an electrolyte in the solution.\nDuring anodization, an oxide layer is formed on the aluminium.\nThe use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.\nThe high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least a change to less toxic chromium(III) compounds.\n# [Stainless steel cutlery made from Cromargan 18/10, containing 18% chromium | upload.wikimedia.org/wikipedia/commons/6/66/Besteck///WMF///Stockholm///ca///1960er.jpg]\n# [Decorative chrome plating on a motorcycle | upload.wikimedia.org/wikipedia/commons/e/e1/Motorcycle///Reflections///bw///edit.jpg]\n\n## Pigment\nThe mineral [crocoite](https://bliptext.com/articles/crocoite) (which is also [lead chromate](https://bliptext.com/articles/lead-chromate) PbCrO4) was used as a yellow pigment shortly after its discovery.\nAfter a synthesis method became available starting from the more abundant chromite, [chrome yellow](https://bliptext.com/articles/chrome-yellow) was, together with [cadmium yellow](https://bliptext.com/articles/cadmium-yellow), one of the most used yellow pigments.\nThe pigment does not photodegrade, but it tends to darken due to the formation of chromium(III) oxide.\nIt has a strong color, and was used for school buses in the United States and for the postal services (for example, the [Deutsche Post](https://bliptext.com/articles/deutsche-post)) in Europe.\nThe use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium.\nOther pigments that are based around chromium are, for example, the deep shade of red pigment [chrome red](https://bliptext.com/articles/chrome-red), which is simply lead chromate with [lead(II) hydroxide](https://bliptext.com/articles/lead-ii-hydroxide) (PbCrO4·Pb(OH)2).\nA very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate.\nA wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution.\nThis used zinc tetroxychromate dispersed in a solution of [polyvinyl butyral](https://bliptext.com/articles/polyvinyl-butyral).\nAn 8% solution of phosphoric acid in solvent was added just before application.\nIt was found that an easily oxidized alcohol was an essential ingredient.\nA thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured.\nThere is still a question as to the correct mechanism.\nChrome green is a mixture of [Prussian blue](https://bliptext.com/articles/prussian-blue) and [chrome yellow](https://bliptext.com/articles/chrome-yellow), while the chrome oxide green is [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium oxides are also used as a green pigment in the field of glassmaking and also as a glaze for ceramics.\nGreen chromium oxide is extremely [lightfast](https://bliptext.com/articles/lightfastness) and as such is used in cladding coatings.\nIt is also the main ingredient in [infrared](https://bliptext.com/articles/infrared) reflecting paints, used by the armed forces to paint vehicles and to give them the same [infrared](https://bliptext.com/articles/infrared) reflectance as green leaves.\n\n## Other uses\nChromium(III) ions present in [corundum](https://bliptext.com/articles/corundum) crystals (aluminium oxide) cause them to be colored red; when [corundum](https://bliptext.com/articles/corundum) appears as such, it is known as a [ruby](https://bliptext.com/articles/ruby).\nIf the corundum is lacking in chromium(III) ions, it is known as a [sapphire](https://bliptext.com/articles/sapphire).\nA red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies.\nSuch a synthetic ruby crystal was the basis for the first [laser](https://bliptext.com/articles/laser), produced in 1960, which relied on [stimulated emission](https://bliptext.com/articles/stimulated-emission) of light from the chromium atoms in such a crystal.\nRuby has a laser transition at 694.3 nanometers, in a deep red color.\nChromium(VI) salts are used for the preservation of wood.\nFor example, [chromated copper arsenate](https://bliptext.com/articles/chromated-copper-arsenate) (CCA) is used in [timber treatment](https://bliptext.com/articles/timber-treatment) to protect wood from decay fungi, wood-attacking insects, including [termites](https://bliptext.com/articles/termites), and marine borers.\nThe formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%.\nIn the United States, 65,300 metric tons of CCA solution were used in 1996.\nChromium(III) salts, especially [chrome alum](https://bliptext.com/articles/chrome-alum) and [chromium(III) sulfate](https://bliptext.com/articles/chromium-iii-sulfate), are used in the tanning of [leather](https://bliptext.com/articles/leather).\nThe chromium(III) stabilizes the leather by cross linking the [collagen](https://bliptext.com/articles/collagen) fibers.\nChromium tanned leather can contain 4–5% of chromium, which is tightly bound to the proteins.\nAlthough the form of chromium used for tanning is not the toxic hexavalent variety, there remains interest in management of chromium in the tanning industry.\nRecovery and reuse, direct/indirect recycling, and \"chrome-less\" or \"chrome-free\" tanning are practiced to better manage chromium usage.\nThe high heat resistivity and high melting point makes [chromite](https://bliptext.com/articles/chromite) and chromium(III) oxide a material for high temperature refractory applications, like [blast furnaces](https://bliptext.com/articles/blast-furnace), cement [kilns](https://bliptext.com/articles/kiln), molds for the firing of [bricks](https://bliptext.com/articles/brick) and as foundry sands for the [casting](https://bliptext.com/articles/casting-metalworking) of metals.\nIn these applications, the refractory materials are made from mixtures of chromite and magnesite.\nThe use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).\nSeveral chromium compounds are used as [catalysts](https://bliptext.com/articles/catalyst) for processing hydrocarbons.\nFor example, the [Phillips catalyst](https://bliptext.com/articles/phillips-catalyst), prepared from chromium oxides, is used for the production of about half the world's [polyethylene](https://bliptext.com/articles/polyethylene).\nFe-Cr mixed oxides are employed as high-temperature catalysts for the [water gas shift reaction](https://bliptext.com/articles/water-gas-shift-reaction).\n[Copper chromite](https://bliptext.com/articles/copper-chromite) is a useful [hydrogenation](https://bliptext.com/articles/hydrogenation) catalyst.\n# [Red crystal of a ruby laser | upload.wikimedia.org/wikipedia/commons/7/7d/5///Maiman///Laser///Components.jpg]\n\n## Uses of compounds\n\n# Biological role\nThe possible nutritional value of chromium(III) is unproven.\nAlthough chromium is regarded as a trace element and [dietary mineral](https://bliptext.com/articles/mineral-nutrient), its suspected roles in the action of [insulin](https://bliptext.com/articles/insulin) – a hormone that mediates the metabolism and storage of carbohydrate, fat, and protein – have not been adequately established.\nThe [mechanism of its actions](https://bliptext.com/articles/mechanism-of-action) in the body is undefined, leaving in doubt whether chromium has a biological role in healthy people.\nIn contrast, [hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium) (Cr(VI) or Cr6+) is highly toxic and [mutagenic](https://bliptext.com/articles/mutagen).\nIngestion of chromium(VI) in water has been linked to stomach tumors, and it may also cause allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis).\n\"[Chromium deficiency](https://bliptext.com/articles/chromium-deficiency)\", involving a lack of Cr(III) in the body, or perhaps some complex of it, such as [glucose tolerance factor](https://bliptext.com/articles/glucose-tolerance-factor), is not accepted as a medical condition, as it has no symptoms and healthy people do not require chromium supplementation.\nSome studies suggest that the biologically active form of chromium(III) is transported in the body via an oligopeptide called [low-molecular-weight chromium-binding substance](https://bliptext.com/articles/low-molecular-weight-chromium-binding-substance) (chromodulin), which might play a role in the insulin signaling pathway.\nThe chromium content of common foods is generally low (1–13 micrograms per serving).\nThe chromium content of food varies widely, due to differences in soil mineral content, growing season, plant [cultivar](https://bliptext.com/articles/cultivar), and contamination during processing.\nChromium (and [nickel](https://bliptext.com/articles/nickel)) leach into food cooked in stainless steel, with the effect being largest when the cookware is new.\nAcidic foods that are cooked for many hours also exacerbate this effect.\n\n## Dietary recommendations\nThere is disagreement on chromium's status as an essential nutrient.\nGovernmental departments from Australia, New Zealand, India, and Japan consider chromium as essential, while the United States and European Food Safety Authority of the European Union do not.\nThe U.S. [National Academy of Medicine](https://bliptext.com/articles/national-academy-of-medicine) (NAM) updated the [Estimated Average Requirements](https://bliptext.com/articles/dietary-reference-intake) (EARs) and the [Recommended Dietary Allowances](https://bliptext.com/articles/dietary-reference-intake) (RDAs) for chromium in 2001.\nFor chromium, there was insufficient information to set EARs and RDAs, so its needs are described as estimates for [Adequate Intake](https://bliptext.com/articles/dietary-reference-intake) (AI).\nFrom a 2001 assessment, AI of chromium for women ages 14 through 50 is 25 μg/day, and the AI for women ages 50 and above is 20 μg/day.\nThe AIs for women who are pregnant are 30 μg/day, and for women who are lactating, the set AI is 45 μg/day.\nThe AI for men ages 14 through 50 is 35 μg/day, and the AI for men ages 50 and above is 30 μg/day.\nFor children ages 1 through 13, the AI increases with age from 0.2 μg/day up to 25 μg/day.\nAs for safety, the NAM sets [Tolerable Upper Intake Levels](https://bliptext.com/articles/dietary-reference-intake) (ULs) for vitamins and minerals when the evidence is sufficient.\nIn the case of chromium, there is not yet enough information, hence no UL has been established.\nCollectively, the EARs, RDAs, AIs, and ULs are the parameters for the nutrition recommendation system known as [Dietary Reference Intake](https://bliptext.com/articles/dietary-reference-intake) (DRI).\nAustralia and New Zealand consider chromium to be an essential nutrient, with an AI of 35 μg/day for men, 25 μg/day for women, 30 μg/day for women who are pregnant, and 45 μg/day for women who are lactating.\nA UL has not been set due to the lack of sufficient data.\nIndia considers chromium to be an essential nutrient, with an adult recommended intake of 33 μg/day.\nJapan also considers chromium to be an essential nutrient, with an AI of 10 μg/day for adults, including women who are pregnant or lactating.\nA UL has not been set.\nThe EFSA does not consider chromium to be an essential nutrient.\n\n### Labeling\nFor U.S. food and dietary supplement labeling purposes, the amount of the substance in a serving is expressed as a percent of the [Daily Value](https://bliptext.com/articles/reference-daily-intake) (%DV).\nFor chromium labeling purposes, 100% of the Daily Value was 120 μg. As of 27 May 2016, the percentage of daily value was revised to 35 μg to bring the chromium intake into a consensus with the official [Recommended Dietary Allowance](https://bliptext.com/articles/dietary-reference-intake).\nA table of the old and new adult daily values in the United States is provided at [Reference Daily Intake](https://bliptext.com/articles/reference-daily-intake).\nAfter evaluation of research on the potential nutritional value of chromium, the European Food Safety Authority concluded that there was no evidence of benefit by dietary chromium in healthy people, thereby declining to establish recommendations in Europe for dietary intake of chromium.\n\n## Food sources\nFood composition databases such as those maintained by the U.S. Department of Agriculture do not contain information on the chromium content of foods.\nA wide variety of animal and vegetable foods contain chromium.\nContent per serving is influenced by the chromium content of the soil in which the plants are grown, by foodstuffs fed to animals, and by processing methods, as chromium is leached into foods if processed or cooked in stainless steel equipment.\nOne diet analysis study conducted in Mexico reported an average daily chromium intake of 30 micrograms.\nAn estimated 31% of adults in the United States consume multi-vitamin/mineral dietary supplements, which often contain 25 to 60 micrograms of chromium.\n\n## Supplementation\nChromium is an ingredient in [total parenteral nutrition](https://bliptext.com/articles/total-parenteral-nutrition) (TPN), because deficiency can occur after months of intravenous feeding with chromium-free TPN.\nIt is also added to nutritional products for [preterm infants](https://bliptext.com/articles/preterm-infant).\nAlthough the mechanism of action in biological roles for chromium is unclear, in the United States chromium-containing products are sold as non-prescription dietary supplements in amounts ranging from 50 to 1,000 μg. Lower amounts of chromium are also often incorporated into multi-vitamin/mineral supplements consumed by an estimated 31% of adults in the United States.\nChemical compounds used in dietary supplements include chromium chloride, chromium citrate, [chromium(III) picolinate](https://bliptext.com/articles/chromium-iii-picolinate), [chromium(III) polynicotinate](https://bliptext.com/articles/chromium-polynicotinate), and other chemical compositions.\nThe benefit of supplements has not been proven.\n\n### Initiation of research on glucose\nThe notion of chromium as a potential regulator of glucose metabolism began in the 1950s when scientists performed a series of experiments controlling the diet of rats.\nThe experimenters subjected the rats to a chromium deficient diet, and witnessed an inability to respond effectively to increased levels of blood glucose.\nA chromium-rich [Brewer's yeast](https://bliptext.com/articles/yeast) was provided in the diet, enabling the rats to effectively metabolize glucose, and so giving evidence that chromium may have a role in glucose management.\n\n## Approved and disapproved health claims\nIn 2005, the U.S. Food and Drug Administration had approved a qualified health claim for chromium picolinate with a requirement for specific label wording:\nIn other parts of the petition, the FDA rejected claims for chromium picolinate and cardiovascular disease, retinopathy or kidney disease caused by abnormally high blood sugar levels.\nAs of March 2024, this ruling on chromium remains in effect.\nIn 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements.\nApproved labeling statements include: a factor in the maintenance of good health, provides support for healthy glucose metabolism, helps the body to metabolize carbohydrates and helps the body to metabolize fats.\nThe European Food Safety Authority approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration, but rejected claims for maintenance or achievement of a normal body weight, or reduction of tiredness or fatigue.\nHowever, in a 2014 reassessment of studies to determine whether a Dietary Reference Intake value could be established for chromium, EFSA stated:\n\n### Diabetes\nGiven the evidence for chromium deficiency causing problems with glucose management in the context of intravenous nutrition products formulated without chromium, research interest turned to whether chromium supplementation would benefit people who have type 2 diabetes but are not chromium deficient.\nLooking at the results from four meta-analyses, one reported a statistically significant decrease in fasting [plasma glucose](https://bliptext.com/articles/plasma-glucose) levels and a non-significant trend in lower [hemoglobin A1C](https://bliptext.com/articles/glycated-hemoglobin).\nA second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either.\nA review published in 2016 listed 53 [randomized clinical trials](https://bliptext.com/articles/randomized-clinical-trial) that were included in one or more of six [meta-analyses](https://bliptext.com/articles/meta-analysis).\nIt concluded that whereas there may be modest decreases in fasting blood glucose and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome.\n\n### Body weight\nTwo [systematic reviews](https://bliptext.com/articles/systematic-review) looked at chromium supplements as a mean of managing body weight in overweight and obese people.\nOne, limited to [chromium picolinate](https://bliptext.com/articles/chromium-picolinate), a common supplement ingredient, reported a statistically significant −1.1 kg (2.4 lb) weight loss in trials longer than 12 weeks.\nThe other included all chromium compounds and reported a statistically significant −0.50 kg (1.1 lb) weight change.\nChange in percent body fat did not reach statistical significance.\nAuthors of both reviews considered the clinical relevance of this modest weight loss as uncertain/unreliable.\nThe European Food Safety Authority reviewed the literature and concluded that there was insufficient evidence to support a claim.\n\n### Sports\nChromium is promoted as a sports performance dietary supplement, based on the theory that it potentiates insulin activity, with anticipated results of increased muscle mass, and faster recovery of glycogen storage during post-exercise recovery.\nA review of clinical trials reported that chromium supplementation did not improve exercise performance or increase muscle strength.\nThe International Olympic Committee reviewed dietary supplements for high-performance athletes in 2018 and concluded there was no need to increase chromium intake for athletes, nor support for claims of losing body fat.\n\n## Fresh-water fish\nIrrigation water standards for chromium are 0.1 mg/L, but some rivers in [Bangladesh](https://bliptext.com/articles/bangladesh) are more than five times that amount.\nThe standard for fish for human consumption is less than 1 mg/kg, but many tested samples were more than five times that amount.\nChromium, especially hexavalent chromium, is highly toxic to fish because it is easily absorbed across the gills, readily enters blood circulation, crosses cell membranes and bioconcentrates up the food chain.\nIn contrast, the toxicity of trivalent chromium is very low, attributed to poor membrane permeability and little biomagnification.\nAcute and chronic exposure to chromium(VI) affects fish behavior, physiology, reproduction and survival.\nHyperactivity and erratic swimming have been reported in contaminated environments.\nEgg hatching and fingerling survival are affected.\nIn adult fish there are reports of histopathological damage to liver, kidney, muscle, intestines, and gills.\nMechanisms include mutagenic gene damage and disruptions of enzyme functions.\nThere is evidence that fish may not require chromium, but benefit from a measured amount in diet.\nIn one study, juvenile fish gained weight on a zero chromium diet, but the addition of 500 μg of chromium in the form of chromium chloride or other supplement types, per kilogram of food (dry weight), increased weight gain.\nAt 2,000 μg/kg the weight gain was no better than with the zero chromium diet, and there were increased DNA strand breaks.\n\n# Precautions\nWater-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.\nBecause of the specific [transport](https://bliptext.com/articles/transport-protein) mechanisms, only limited amounts of chromium(III) enter the cells.\nAcute oral toxicity ranges between 50 and 150 mg/kg.\nA 2008 review suggested that moderate uptake of chromium(III) through dietary supplements poses no genetic-toxic risk.\nIn the US, the [Occupational Safety and Health Administration](https://bliptext.com/articles/occupational-safety-and-health-administration) (OSHA) has designated an air [permissible exposure limit](https://bliptext.com/articles/permissible-exposure-limit) (PEL) in the workplace as a time-weighted average (TWA) of 1 mg/m3.\nThe [National Institute for Occupational Safety and Health](https://bliptext.com/articles/national-institute-for-occupational-safety-and-health) (NIOSH) has set a [recommended exposure limit](https://bliptext.com/articles/recommended-exposure-limit) (REL) of 0.5 mg/m3, time-weighted average.\nThe [IDLH](https://bliptext.com/articles/idlh) (immediately dangerous to life and health) value is 250 mg/m3.\n\n## Chromium(VI) toxicity\nThe acute [oral](https://bliptext.com/articles/mouth) [toxicity](https://bliptext.com/articles/toxicity) for [chromium(VI)](https://bliptext.com/articles/hexavalent-chromium) ranges between 1.5 and 3.3 mg/kg.\nIn the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells.\nThe chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also [sulfate](https://bliptext.com/articles/sulfate) and [phosphate](https://bliptext.com/articles/phosphate) ions enter the cell.\nThe acute toxicity of chromium(VI) is due to its strong [oxidant](https://bliptext.com/articles/redox) properties.\nAfter it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions.\n[Hemolysis](https://bliptext.com/articles/hemolysis), [renal](https://bliptext.com/articles/renal), and liver failure result.\nAggressive dialysis can be therapeutic.\nThe [carcinogenity](https://bliptext.com/articles/carcinogenity) of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.\nThree mechanisms have been proposed to describe the [genotoxicity](https://bliptext.com/articles/genotoxicity) of chromium(VI).\nThe first mechanism includes highly reactive [hydroxyl radicals](https://bliptext.com/articles/hydroxyl-radical) and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III).\nThe second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the [DNA](https://bliptext.com/articles/dna).\nThe last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.\nChromium salts (chromates) are also the cause of [allergic reactions](https://bliptext.com/articles/allergic-reaction) in some people.\nChromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.\nContact with products containing chromates can lead to allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis) and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as \"chrome ulcers\".\nThis condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.\n\n## Environmental issues\nBecause chromium compounds were used in [dyes](https://bliptext.com/articles/dye), [paints](https://bliptext.com/articles/paint), and [leather](https://bliptext.com/articles/leather) [tanning](https://bliptext.com/articles/tanning-leather) compounds, these compounds are often found in soil and [groundwater](https://bliptext.com/articles/groundwater) at active and abandoned industrial sites, needing [environmental cleanup](https://bliptext.com/articles/environmental-cleanup) and [remediation](https://bliptext.com/articles/environmental-remediation).\n[Primer paint](https://bliptext.com/articles/primer-paint) containing hexavalent chromium is still widely used for [aerospace](https://bliptext.com/articles/aerospace) and [automobile](https://bliptext.com/articles/automobile) refinishing applications.\nIn 2010, the [Environmental Working Group](https://bliptext.com/articles/environmental-working-group) studied the drinking water in 35 American cities in the first nationwide study.\nThe study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with [Norman, Oklahoma](https://bliptext.com/articles/norman-oklahoma), at the top of list; 25 cities had levels that exceeded California's proposed limit.\nThe more toxic hexavalent chromium form can be reduced to the less soluble trivalent oxidation state in soils by organic matter, ferrous iron, sulfides, and other reducing agents, with the rates of such reduction being faster under more acidic conditions than under more alkaline ones.\nIn contrast, trivalent chromium can be oxidized to hexavalent chromium in soils by manganese oxides, such as Mn(III) and Mn(IV) compounds.\nSince the solubility and toxicity of chromium (VI) are greater that those of chromium (III), the oxidation-reduction conversions between the two oxidation states have implications for movement and bioavailability of chromium in soils, groundwater, and plants.\n\n# General bibliography","current_revision":"ac3ae573-94ba-44be-883f-11f311a1ee5c","created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T17:20:07.202Z","updated_at":"2025-03-18T15:16:43.866Z","search_vector":"'chromium':1","search_content":" \n**Vickers Hardness:** 950HV \n**Vickers Hardness Ref:** https://www.journalmt.com/pdfs/mft/2018/04/16.pdf \n \n\n# \n**Chromium** is a [chemical element](https://bliptext.com/articles/chemical-element); it has [symbol](https://bliptext.com/articles/symbol-chemistry) **Cr** and [atomic number](https://bliptext.com/articles/atomic-number) 24.\nIt is the first element in [group 6](https://bliptext.com/articles/group-6-element).\nIt is a steely-grey, [lustrous](https://bliptext.com/articles/luster-mineralogy), hard, and brittle [transition metal](https://bliptext.com/articles/transition-metal).\nChromium is valued for its high [corrosion](https://bliptext.com/articles/corrosion) resistance and [hardness](https://bliptext.com/articles/hardness).\nA major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form [stainless steel](https://bliptext.com/articles/stainless-steel).\nStainless steel and [chrome plating](https://bliptext.com/articles/chrome-plating) ([electroplating](https://bliptext.com/articles/electroplating) with chromium) together comprise 85% of the commercial use.\nChromium is also greatly valued as a [metal](https://bliptext.com/articles/metal) that is able to be highly [polished](https://bliptext.com/articles/polishing) while resisting [tarnishing](https://bliptext.com/articles/tarnish).\nPolished chromium reflects almost 70% of the [visible spectrum](https://bliptext.com/articles/visible-spectrum), and almost 90% of [infrared light](https://bliptext.com/articles/infrared).\nThe name of the element is derived from the [Greek](https://bliptext.com/articles/ancient-greek) word χρῶμα, chrōma, meaning [color](https://bliptext.com/articles/color), because many chromium compounds are intensely [color](https://bliptext.com/articles/color)ed.\nIndustrial production of chromium proceeds from [chromite](https://bliptext.com/articles/chromite) ore (mostly FeCr2O4) to produce [ferrochromium](https://bliptext.com/articles/ferrochromium), an iron-chromium alloy, by means of [aluminothermic](https://bliptext.com/articles/aluminothermic-reaction) or [silicothermic reactions](https://bliptext.com/articles/silicothermic-reaction).\nFerrochromium is then used to produce alloys such as stainless steel.\nPure chromium metal is produced by a different process: [roasting](https://bliptext.com/articles/roasting-metallurgy) and [leaching](https://bliptext.com/articles/leaching-metallurgy) of chromite to separate it from iron, followed by reduction with [carbon](https://bliptext.com/articles/carbon) and then [aluminium](https://bliptext.com/articles/aluminium).\n[Trivalent](https://bliptext.com/articles/trivalent) chromium (Cr(III)) occurs naturally in many foods and is sold as a [dietary supplement](https://bliptext.com/articles/dietary-supplement), although there is insufficient evidence that dietary chromium provides nutritional benefit to people.\nIn 2014, the [European Food Safety Authority](https://bliptext.com/articles/european-food-safety-authority) concluded that research on dietary chromium did not justify it to be recognized as an essential [nutrient](https://bliptext.com/articles/nutrient).\nWhile chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called \"[hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium)\", is toxic and [carcinogenic](https://bliptext.com/articles/carcinogenic).\nAccording to the European Chemicals Agency (ECHA), [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) that is used in industrial electroplating processes is a \"substance of very high concern\" (SVHC).\n\n# Physical properties\n\n## Atomic\nGaseous chromium has a ground-state [electron configuration](https://bliptext.com/articles/electron-configuration) of [ [Ar](https://bliptext.com/articles/argon)] 3d5 4s1.\nIt is the first element in the periodic table whose configuration violates the [Aufbau principle](https://bliptext.com/articles/aufbau-principle).\nExceptions to the principle also occur later in the periodic table for elements such as [copper](https://bliptext.com/articles/copper), [niobium](https://bliptext.com/articles/niobium) and [molybdenum](https://bliptext.com/articles/molybdenum).\nChromium is the first element in the 3d series where the 3d electrons start to sink into the core; they thus contribute less to [metallic bonding](https://bliptext.com/articles/metallic-bonding), and hence the melting and boiling points and the [enthalpy of atomisation](https://bliptext.com/articles/enthalpy-of-atomisation) of chromium are lower than those of the preceding element [vanadium](https://bliptext.com/articles/vanadium).\nChromium(VI) is a strong [oxidising agent](https://bliptext.com/articles/oxidising-agent) in contrast to the [molybdenum](https://bliptext.com/articles/molybdenum)(VI) and [tungsten](https://bliptext.com/articles/tungsten)(VI) oxides.\n\n## Bulk\nChromium is the third hardest element after [carbon](https://bliptext.com/articles/carbon) ([diamond](https://bliptext.com/articles/diamond)) and [boron](https://bliptext.com/articles/boron).\nIts [Mohs hardness](https://bliptext.com/articles/mohs-scale-of-mineral-hardness) is 8.5, which means that it can scratch samples of [quartz](https://bliptext.com/articles/quartz) and [topaz](https://bliptext.com/articles/topaz), but can be scratched by [corundum](https://bliptext.com/articles/corundum).\nChromium is highly resistant to [tarnishing](https://bliptext.com/articles/tarnish), which makes it useful as a metal that preserves its outermost layer from [corroding](https://bliptext.com/articles/corrosion), unlike other metals such as [copper](https://bliptext.com/articles/copper), [magnesium](https://bliptext.com/articles/magnesium), and [aluminium](https://bliptext.com/articles/aluminium).\nChromium has a [melting point](https://bliptext.com/articles/melting-point) of 1907 °C (3465 °F), which is relatively low compared to the majority of transition metals.\nHowever, it still has the second highest melting point out of all the [period 4 elements](https://bliptext.com/articles/period-4-element), being topped by [vanadium](https://bliptext.com/articles/vanadium) by 3 °C (5 °F) at 1910 °C (3470 °F).\nThe [boiling point](https://bliptext.com/articles/boiling-point) of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest [boiling point](https://bliptext.com/articles/boiling-point) out of the [Period 4](https://bliptext.com/articles/period-4) [transition metals](https://bliptext.com/articles/transition-metal) alone behind [copper](https://bliptext.com/articles/copper), [manganese](https://bliptext.com/articles/manganese) and [zinc](https://bliptext.com/articles/zinc).\nThe [electrical resistivity](https://bliptext.com/articles/electrical-resistivity-and-conductivity) of chromium at 20 °C is 125 [nanoohm](https://bliptext.com/articles/ohm)-[meters](https://bliptext.com/articles/meter).\nChromium has a high [specular reflection](https://bliptext.com/articles/specular-reflection) in comparison to other transition metals.\nIn [infrared](https://bliptext.com/articles/infrared), at 425 [μm](https://bliptext.com/articles/micrometre), chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 [μm](https://bliptext.com/articles/micrometre) before rising again to 90% at 4000 [μm](https://bliptext.com/articles/micrometre).\nWhen chromium is used in [stainless steel](https://bliptext.com/articles/stainless-steel) alloys and [polished](https://bliptext.com/articles/polishing), the specular reflection decreases with the inclusion of additional metals, yet is still high in comparison with other alloys.\nBetween 40% and 60% of the visible spectrum is reflected from polished stainless steel.\nThe explanation on why chromium displays such a high turnout of reflected [photon](https://bliptext.com/articles/photon) waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties.\nChromium has unique magnetic properties; it is the only elemental solid that shows [antiferromagnetic](https://bliptext.com/articles/antiferromagnetic) ordering at room temperature and below.\nAbove 38 °C, its magnetic ordering becomes [paramagnetic](https://bliptext.com/articles/paramagnetic).\nThe antiferromagnetic properties, which cause the chromium atoms to temporarily [ionize](https://bliptext.com/articles/ionization) and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the [lattice periodicity](https://bliptext.com/articles/crystal-structure).\nThis is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers.\nFrom here, the frequency-dependent [relative permittivity](https://bliptext.com/articles/relative-permittivity) of chromium, deriving from [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations) and chromium's [antiferromagnetism](https://bliptext.com/articles/antiferromagnetism), leaves chromium with a high infrared and visible light reflectance.\n# [Sample of chromium metal | upload.wikimedia.org/wikipedia/commons/a/a1/Chromium.jpg]\n\n### Passivation\nChromium metal in air is [passivated](https://bliptext.com/articles/passivation-chemistry): it forms a thin, protective surface layer of chromium oxide with the [corundum](https://bliptext.com/articles/corundum-structure) structure.\nPassivation can be enhanced by short contact with [oxidizing acids](https://bliptext.com/articles/oxidizing-acid) like [nitric acid](https://bliptext.com/articles/nitric-acid).\nPassivated chromium is stable against acids.\nPassivation can be removed with a strong [reducing agent](https://bliptext.com/articles/reducing-agent) that destroys the protective oxide layer on the metal.\nChromium metal treated in this way readily dissolves in weak acids.\nThe surface [chromia](https://bliptext.com/articles/chromium-iii-oxide) Cr2O3 scale, is adherent to the metal.\nIn contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued [rusting](https://bliptext.com/articles/rust).\nAt room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward [diffusion](https://bliptext.com/articles/atomic-diffusion) of metal ions across the scale.\nAbove 950 °C volatile [chromium trioxide](https://bliptext.com/articles/chromium-trioxide) CrO3 forms from the chromia scale, limiting the scale thickness and oxidation protection.\nChromium, unlike iron and nickel, does not suffer from [hydrogen embrittlement](https://bliptext.com/articles/hydrogen-embrittlement).\nHowever, it does suffer from nitrogen [embrittlement](https://bliptext.com/articles/embrittlement), reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.\n\n## Isotopes\nNaturally occurring chromium is composed of four stable [isotopes](https://bliptext.com/articles/isotope); 50Cr, 52Cr, 53Cr and 54Cr, with 52Cr being the most abundant (83.789% [natural abundance](https://bliptext.com/articles/natural-abundance)).\n50Cr is [observationally stable](https://bliptext.com/articles/stable-nuclide), as it is theoretically capable of [decaying](https://bliptext.com/articles/radioactive-decay) to [50Ti](https://bliptext.com/articles/isotopes-of-titanium) via [double electron capture](https://bliptext.com/articles/double-electron-capture) with a [half-life](https://bliptext.com/articles/half-life) of no less than 1.3 years.\nTwenty-five [radioisotopes](https://bliptext.com/articles/radioisotope) have been characterized, ranging from 42Cr to 70Cr; the most stable radioisotope is 51Cr with a half-life of 27.7 days.\nAll of the remaining [radioactive](https://bliptext.com/articles/radioactive) isotopes have half-lives that are less than 24 hours and the majority less than 1 minute.\nChromium also has two [metastable](https://bliptext.com/articles/metastable) [nuclear isomers](https://bliptext.com/articles/nuclear-isomer).\nThe primary [decay mode](https://bliptext.com/articles/decay-mode) before the most abundant stable isotope, 52Cr, is [electron capture](https://bliptext.com/articles/electron-capture) and the primary mode after is [beta decay](https://bliptext.com/articles/beta-decay).\n53Cr is the [radiogenic](https://bliptext.com/articles/radiogenic) decay product of 53[Mn](https://bliptext.com/articles/manganese) (half-life 3.74 million years).\nChromium isotopes are typically collocated (and compounded) with [manganese](https://bliptext.com/articles/manganese) isotopes.\nThis circumstance is useful in [isotope geology](https://bliptext.com/articles/isotope-geology).\nManganese-chromium isotope ratios reinforce the evidence from [26Al](https://bliptext.com/articles/aluminium-26) and 107[Pd](https://bliptext.com/articles/palladium) concerning the early history of the [Solar System](https://bliptext.com/articles/solar-system).\nVariations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies.\nHence 53Cr provides additional evidence for [nucleosynthetic](https://bliptext.com/articles/nucleosynthesis) processes immediately before coalescence of the Solar System.\n53Cr has been posited as a proxy for atmospheric oxygen concentration.\n\n# Chemistry and compounds\nChromium is a member of [group 6](https://bliptext.com/articles/group-6-element), of the [transition metals](https://bliptext.com/articles/transition-metal).\nThe +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.\n# [The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide | upload.wikimedia.org/wikipedia/commons/c/c3/Chromium///in///water///pourbiax///diagram.png]\n\n## Common oxidation states\n\n### Chromium(0)\nMany Cr(0) complexes are known.\n[Bis(benzene)chromium](https://bliptext.com/articles/bis-benzene-chromium) and [chromium hexacarbonyl](https://bliptext.com/articles/chromium-hexacarbonyl) are highlights in [organochromium chemistry](https://bliptext.com/articles/organochromium-chemistry).\n\n### Chromium(II)\nChromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air.\nWater-stable [chromium(II) chloride](https://bliptext.com/articles/chromium-ii-chloride) that can be made by reducing chromium(III) chloride with zinc.\nThe resulting bright blue solution created from dissolving chromium(II) chloride is stable at neutral [pH](https://bliptext.com/articles/ph).\nSome other notable chromium(II) compounds include [chromium(II) oxide](https://bliptext.com/articles/chromium-ii-oxide), and [chromium(II) sulfate](https://bliptext.com/articles/chromium-ii-sulfate).\nMany chromium(II) carboxylates are known.\nThe red [chromium(II) acetate](https://bliptext.com/articles/chromium-ii-acetate) (Cr2(O2CCH3)4) is somewhat famous.\nIt features a Cr-Cr [quadruple bond](https://bliptext.com/articles/quadruple-bond).\n# [Chromium(II) carbide (Cr3C2) | upload.wikimedia.org/wikipedia/commons/e/eb/Chromium///carbide///Cr3C2.JPG]\n\n### Chromium(III)\nA large number of chromium(III) compounds are known, such as [chromium(III) nitrate](https://bliptext.com/articles/chromium-nitrate), [chromium(III) acetate](https://bliptext.com/articles/chromium-iii-acetate), and [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium(III) can be obtained by dissolving elemental chromium in acids like [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid) or [sulfuric acid](https://bliptext.com/articles/sulfuric-acid), but it can also be formed through the reduction of chromium(VI) by [cytochrome](https://bliptext.com/articles/cytochrome) [c7](https://bliptext.com/articles/cytochrome-c).\nThe ion has a similar radius (63 [pm](https://bliptext.com/articles/picometer)) to (radius 50 [pm](https://bliptext.com/articles/picometer)), and they can replace each other in some compounds, such as in [chrome [alum](https://bliptext.com/articles/alum)](https://bliptext.com/articles/chrome-[alum](https://bliptext.com/articles/alum)) and [alum](https://bliptext.com/articles/alum).\nChromium(III) tends to form [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) complexes.\nCommercially available [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) hydrate is the dark green complex [CrCl2(H2O)4]Cl.\nClosely related compounds are the pale green [CrCl(H2O)5]Cl2 and violet [Cr(H2O)6]Cl3.\nIf anhydrous violet [chromium(III) chloride](https://bliptext.com/articles/chromium-iii-chloride) is dissolved in water, the violet solution turns green after some time as the chloride in the inner [coordination sphere](https://bliptext.com/articles/coordination-sphere) is replaced by water.\nThis kind of reaction is also observed with solutions of [chrome alum](https://bliptext.com/articles/chrome-alum) and other water-soluble chromium(III) salts.\nA [tetrahedral](https://bliptext.com/articles/tetrahedral-molecular-geometry) coordination of [chromium(III)](https://bliptext.com/articles/chromium-iii) has been reported for the Cr-centered [Keggin](https://bliptext.com/articles/keggin-structure) anion [α-CrW12O40]5–.\n[Chromium(III) hydroxide](https://bliptext.com/articles/chromium-iii-hydroxide) (Cr(OH)3) is [amphoteric](https://bliptext.com/articles/amphoterism), dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form.\nIt is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), a stable oxide with a crystal structure identical to that of [corundum](https://bliptext.com/articles/corundum).\n# [Anhydrous chromium(III) chloride (CrCl3) | upload.wikimedia.org/wikipedia/commons/3/3b/Chromium%28III%29-chloride-purple-anhydrous-sunlight.jpg]\n\n### Chromium(VI)\n[Chromium(VI) compounds](https://bliptext.com/articles/hexavalent-chromium) are oxidants at low or neutral pH.\n[Chromate](https://bliptext.com/articles/chromate-and-[dichromate](https://bliptext.com/articles/chromate-and-dichromate)) anions and [dichromate](https://bliptext.com/articles/chromate-and-dichromate) (Cr2O72−) anions are the principal ions at this oxidation state.\nThey exist at an equilibrium, determined by pH:\nChromium(VI) oxyhalides are known also and include [chromyl fluoride](https://bliptext.com/articles/chromyl-fluoride) (CrO2F2) and [chromyl chloride](https://bliptext.com/articles/chromyl-chloride).\nHowever, despite several erroneous claims, [chromium hexafluoride](https://bliptext.com/articles/chromium-hexafluoride) (as well as all higher hexahalides) remains unknown, as of 2020.\n[Sodium chromate](https://bliptext.com/articles/sodium-chromate) is produced industrially by the oxidative roasting of [chromite](https://bliptext.com/articles/chromite) ore with [sodium carbonate](https://bliptext.com/articles/sodium-carbonate).\nThe change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of [potassium chromate](https://bliptext.com/articles/potassium-chromate).\nAt yet lower pH values, further condensation to more complex [oxyanions](https://bliptext.com/articles/oxyanion) of chromium is possible.\nBoth the [chromate and dichromate](https://bliptext.com/articles/chromate-and-dichromate) anions are strong oxidizing reagents at low pH:\nThey are, however, only moderately oxidizing at high pH:\nChromium(VI) compounds in solution can be detected by adding an acidic [hydrogen peroxide](https://bliptext.com/articles/hydrogen-peroxide) solution.\nThe unstable dark blue [chromium(VI) peroxide](https://bliptext.com/articles/chromium-vi-peroxide) (CrO5) is formed, which can be stabilized as an ether adduct.\n[Chromic acid](https://bliptext.com/articles/chromic-acid) has the hypothetical formula.\nIt is a vaguely described chemical, despite many well-defined chromates and dichromates being known.\nThe dark red [chromium(VI) oxide](https://bliptext.com/articles/chromium-vi-oxide), the acid [anhydride](https://bliptext.com/articles/anhydride) of chromic acid, is sold industrially as \"chromic acid\".\nIt can be produced by mixing sulfuric acid with dichromate and is a strong oxidizing agent.\n# [Chromium(VI) oxide | upload.wikimedia.org/wikipedia/commons/1/1e/Chrom%28VI%29-oxid.jpg]\n# [Sodium chromate (Na2CrO4) | upload.wikimedia.org/wikipedia/commons/5/51/Chroman///sodn%C3%BD.JPG]\n\n## Other oxidation states\nCompounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate.\nThe only binary compound is the volatile [chromium(V) fluoride](https://bliptext.com/articles/chromium-v-fluoride) (CrF5).\nThis red solid has a melting point of 30 °C and a boiling point of 117 °C.\nIt can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure.\nThe peroxochromate(V) is another example of the +5 oxidation state.\n[Potassium peroxochromate](https://bliptext.com/articles/potassium-tetraperoxochromate-v) (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures.\nThis red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.\nCompounds of chromium(IV) are slightly more common than those of chromium(V).\nThe tetrahalides, [CrF4](https://bliptext.com/articles/chromium-iv-fluoride), [CrCl4](https://bliptext.com/articles/chromium-iv-chloride), and CrBr4, can be produced by treating the trihalides with the corresponding halogen at elevated temperatures.\nSuch compounds are susceptible to disproportionation reactions and are not stable in water.\nOrganic compounds containing Cr(IV) state such as chromium tetra t-butoxide are also known.\nMost chromium(I) compounds are obtained solely by oxidation of electron-rich, [octahedral](https://bliptext.com/articles/octahedral-molecular-geometry) chromium(0) complexes.\nOther chromium(I) complexes contain [cyclopentadienyl](https://bliptext.com/articles/cyclopentadienyl) ligands.\nAs verified by [X-ray diffraction](https://bliptext.com/articles/x-ray-diffraction), a Cr-Cr [quintuple bond](https://bliptext.com/articles/quintuple-bond) (length 183.51(4) pm) has also been described.\nExtremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.\n# [Chromium compound determined experimentally to contain a Cr-Cr quintuple bond | upload.wikimedia.org/wikipedia/commons/6/60/5-fold///chromium.png]\n\n# Occurrence\nChromium is the 21st most [abundant element in Earth's crust](https://bliptext.com/articles/abundance-of-elements-in-earth-s-crust) with an average concentration of 100 ppm.\nChromium compounds are found in the environment from the [erosion](https://bliptext.com/articles/erosion) of chromium-containing rocks, and can be redistributed by volcanic eruptions.\nTypical background concentrations of chromium in environmental media are: atmosphere <10 ng/m3; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg.\nChromium is mined as chromite (FeCr2O4) ore.\nAbout two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers.\nUntapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.\nAlthough rare, deposits of [native](https://bliptext.com/articles/native-metal) chromium exist.\nThe [Udachnaya Pipe](https://bliptext.com/articles/udachnaya-pipe) in Russia produces samples of the native metal.\nThis mine is a [kimberlite](https://bliptext.com/articles/kimberlite) pipe, rich in [diamonds](https://bliptext.com/articles/diamond), and the [reducing environment](https://bliptext.com/articles/redox) helped produce both elemental chromium and [diamonds](https://bliptext.com/articles/diamond).\nThe relation between Cr(III) and Cr(VI) strongly depends on [pH](https://bliptext.com/articles/ph) and [oxidative](https://bliptext.com/articles/oxidative) properties of the location.\nIn most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L is Cr(VI).\n# [Crocoite (PbCrO4) | upload.wikimedia.org/wikipedia/commons/a/ac/Crocoite///from///Tasmania.jpg]\n# [Chromite ore | upload.wikimedia.org/wikipedia/commons/0/00/Chromit///1.jpg]\n\n# History\n\n## Early applications\nChromium minerals as pigments came to the attention of the west in the eighteenth century.\nOn 26 July 1761, [Johann Gottlob Lehmann](https://bliptext.com/articles/johann-gottlob-lehmann-scientist) found an orange-red mineral in the [Beryozovskoye mines](https://bliptext.com/articles/beryozovskoye-deposit) in the [Ural Mountains](https://bliptext.com/articles/ural-mountains) which he named Siberian red lead.\nThough misidentified as a [lead](https://bliptext.com/articles/lead) compound with [selenium](https://bliptext.com/articles/selenium) and [iron](https://bliptext.com/articles/iron) components, the mineral was in fact [crocoite](https://bliptext.com/articles/crocoite) with a formula of PbCrO4.\nIn 1770, [Peter Simon Pallas](https://bliptext.com/articles/peter-simon-pallas) visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a [pigment](https://bliptext.com/articles/pigment) in [paints](https://bliptext.com/articles/paint).\nAfter Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region.\nCrocoite would be the principal source of chromium in pigments until the discovery of [chromite](https://bliptext.com/articles/chromite) many years later.\nIn 1794, [Louis Nicolas Vauquelin](https://bliptext.com/articles/louis-nicolas-vauquelin) received samples of crocoite [ore](https://bliptext.com/articles/ore).\nHe produced [chromium trioxide](https://bliptext.com/articles/chromium-vi-oxide) (CrO3) by mixing crocoite with [hydrochloric acid](https://bliptext.com/articles/hydrochloric-acid).\nIn 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.\nVauquelin was also able to detect traces of chromium in precious [gemstones](https://bliptext.com/articles/gemstone), such as [ruby](https://bliptext.com/articles/ruby) and [emerald](https://bliptext.com/articles/emerald).\nDuring the nineteenth century, chromium was primarily used not only as a component of paints, but in [tanning](https://bliptext.com/articles/tanning-leather) salts as well.\nFor quite some time, the crocoite found in Russia was the main source for such tanning materials.\nIn 1827, a larger chromite deposit was discovered near [Baltimore](https://bliptext.com/articles/baltimore), United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.\nThis made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of [Bursa](https://bliptext.com/articles/bursa), Turkey.\nWith the development of metallurgy and chemical industries in the Western world, the need for chromium increased.\nChromium is also famous for its reflective, metallic luster when polished.\nIt is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by [electroplating](https://bliptext.com/articles/electroplating).\nChromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.\n# [The red color of rubies is due to trace amounts of chromium within the corundum. | upload.wikimedia.org/wikipedia/commons/c/c4/Cut///Ruby.jpg]\n\n# Production\nApproximately 28.8 million metric tons (Mt) of marketable chromite ore was produced in 2013, and converted into 7.5 Mt of ferrochromium.\nAccording to John F. Papp, writing for the USGS, \"Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium.\"\nThe largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing the rest of about 18% of the world production.\nThe two main products of chromium ore refining are [ferrochromium](https://bliptext.com/articles/ferrochromium) and metallic chromium.\nFor those products the ore smelter process differs considerably.\nFor the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in [electric arc furnace](https://bliptext.com/articles/electric-arc-furnace) or in smaller smelters with either [aluminium](https://bliptext.com/articles/aluminium) or [silicon](https://bliptext.com/articles/silicon) in an [aluminothermic reaction](https://bliptext.com/articles/aluminothermic-reaction).\nFor the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process.\nThe chromite ore is heated with a mixture of [calcium carbonate](https://bliptext.com/articles/calcium-carbonate) and [sodium carbonate](https://bliptext.com/articles/sodium-carbonate) in the presence of air.\nThe chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.\nThe subsequent leaching at higher elevated temperatures dissolves the [chromates](https://bliptext.com/articles/chromates) and leaves the insoluble iron oxide.\nThe chromate is converted by [sulfuric acid](https://bliptext.com/articles/sulfuric-acid) into the dichromate.\nThe dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.\n# [Piece of chromium produced with aluminothermic reaction | upload.wikimedia.org/wikipedia/commons/c/cf/Chrom///1.jpg]\n# [World production trend of chromium | upload.wikimedia.org/wikipedia/commons/5/5f/Chromium///-///world///production///trend.svg]\n# [Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains | upload.wikimedia.org/wikipedia/commons/4/42/Chromium///zone///refined///and///1cm3///cube.jpg]\n# [Chromium ore output in 2002 | upload.wikimedia.org/wikipedia/commons/2/2c/World///Chromium///Production///2002.svg]\n\n# Applications\nThe creation of metal alloys account for 85% of the available chromium's usage.\nThe remainder of chromium is used in the [chemical](https://bliptext.com/articles/chemical-industry), [refractory](https://bliptext.com/articles/refractory), and [foundry](https://bliptext.com/articles/foundry) industries.\n\n## Metallurgy\nThe strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.\n[High-speed tool steels](https://bliptext.com/articles/high-speed-steel) contain 3–5% chromium.\n[Stainless steel](https://bliptext.com/articles/stainless-steel), the primary corrosion-resistant metal alloy, is formed when chromium is introduced to [iron](https://bliptext.com/articles/iron) in concentrations above 11%.\nFor stainless steel's formation, ferrochromium is added to the molten iron.\nAlso, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries.\nFor example, [Inconel](https://bliptext.com/articles/inconel) 718 contains 18.6% chromium.\nBecause of the excellent high-temperature properties of these nickel [superalloys](https://bliptext.com/articles/superalloy), they are used in [jet engines](https://bliptext.com/articles/jet-engine) and [gas turbines](https://bliptext.com/articles/gas-turbine) in lieu of common structural materials.\n[ASTM](https://bliptext.com/articles/astm) B163 relies on chromium for condenser and heat-exchanger tubes, while [castings](https://bliptext.com/articles/castings) with high strength at elevated temperatures that contain chromium are standardised with [ASTM](https://bliptext.com/articles/astm) A567.\n[AISI](https://bliptext.com/articles/american-iron-and-steel-institute) type 332 is used where high temperature would normally cause [carburization](https://bliptext.com/articles/carburization), [oxidation](https://bliptext.com/articles/oxidation) or [corrosion](https://bliptext.com/articles/corrosion).\n[Incoloy](https://bliptext.com/articles/incoloy) 800 \"is capable of remaining stable and maintaining its [austenitic](https://bliptext.com/articles/austenitic) structure even after long time exposures to high temperatures\".\n[Nichrome](https://bliptext.com/articles/nichrome) is used as resistance wire for heating elements in things like [toasters](https://bliptext.com/articles/toasters) and space heaters.\nThese uses make chromium a [strategic material](https://bliptext.com/articles/strategic-material).\nConsequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it \"may become a critical material during the emergency\".\nThe United States likewise considered chromium \"essential for the German war industry\" and made intense diplomatic efforts to keep it out of the hands of [Nazi Germany](https://bliptext.com/articles/nazi-germany).\nThe high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals.\nA layer of chromium is deposited on pretreated metallic surfaces by [electroplating](https://bliptext.com/articles/electroplating) techniques.\nThere are two deposition methods: thin, and thick.\nThin deposition involves a layer of chromium below 1 μm thickness deposited by [chrome plating](https://bliptext.com/articles/chrome-plating), and is used for decorative surfaces.\nThicker chromium layers are deposited if wear-resistant surfaces are needed.\nBoth methods use acidic chromate or [dichromate](https://bliptext.com/articles/dichromate) solutions.\nTo prevent the energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used.\nIn the [chromate conversion coating](https://bliptext.com/articles/chromate-conversion-coating) process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium.\nThis [passivation](https://bliptext.com/articles/passivation-chemistry) and the self-healing properties of the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.\nBecause of environmental and health regulations on chromates, alternative coating methods are under development.\nChromic acid [anodizing](https://bliptext.com/articles/anodizing) (or Type I [anodizing](https://bliptext.com/articles/anodizing)) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses [chromic acid](https://bliptext.com/articles/chromic-acid) as an electrolyte in the solution.\nDuring anodization, an oxide layer is formed on the aluminium.\nThe use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.\nThe high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least a change to less toxic chromium(III) compounds.\n# [Stainless steel cutlery made from Cromargan 18/10, containing 18% chromium | upload.wikimedia.org/wikipedia/commons/6/66/Besteck///WMF///Stockholm///ca///1960er.jpg]\n# [Decorative chrome plating on a motorcycle | upload.wikimedia.org/wikipedia/commons/e/e1/Motorcycle///Reflections///bw///edit.jpg]\n\n## Pigment\nThe mineral [crocoite](https://bliptext.com/articles/crocoite) (which is also [lead chromate](https://bliptext.com/articles/lead-chromate) PbCrO4) was used as a yellow pigment shortly after its discovery.\nAfter a synthesis method became available starting from the more abundant chromite, [chrome yellow](https://bliptext.com/articles/chrome-yellow) was, together with [cadmium yellow](https://bliptext.com/articles/cadmium-yellow), one of the most used yellow pigments.\nThe pigment does not photodegrade, but it tends to darken due to the formation of chromium(III) oxide.\nIt has a strong color, and was used for school buses in the United States and for the postal services (for example, the [Deutsche Post](https://bliptext.com/articles/deutsche-post)) in Europe.\nThe use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium.\nOther pigments that are based around chromium are, for example, the deep shade of red pigment [chrome red](https://bliptext.com/articles/chrome-red), which is simply lead chromate with [lead(II) hydroxide](https://bliptext.com/articles/lead-ii-hydroxide) (PbCrO4·Pb(OH)2).\nA very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate.\nA wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution.\nThis used zinc tetroxychromate dispersed in a solution of [polyvinyl butyral](https://bliptext.com/articles/polyvinyl-butyral).\nAn 8% solution of phosphoric acid in solvent was added just before application.\nIt was found that an easily oxidized alcohol was an essential ingredient.\nA thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured.\nThere is still a question as to the correct mechanism.\nChrome green is a mixture of [Prussian blue](https://bliptext.com/articles/prussian-blue) and [chrome yellow](https://bliptext.com/articles/chrome-yellow), while the chrome oxide green is [chromium(III) oxide](https://bliptext.com/articles/chromium-iii-oxide).\nChromium oxides are also used as a green pigment in the field of glassmaking and also as a glaze for ceramics.\nGreen chromium oxide is extremely [lightfast](https://bliptext.com/articles/lightfastness) and as such is used in cladding coatings.\nIt is also the main ingredient in [infrared](https://bliptext.com/articles/infrared) reflecting paints, used by the armed forces to paint vehicles and to give them the same [infrared](https://bliptext.com/articles/infrared) reflectance as green leaves.\n\n## Other uses\nChromium(III) ions present in [corundum](https://bliptext.com/articles/corundum) crystals (aluminium oxide) cause them to be colored red; when [corundum](https://bliptext.com/articles/corundum) appears as such, it is known as a [ruby](https://bliptext.com/articles/ruby).\nIf the corundum is lacking in chromium(III) ions, it is known as a [sapphire](https://bliptext.com/articles/sapphire).\nA red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies.\nSuch a synthetic ruby crystal was the basis for the first [laser](https://bliptext.com/articles/laser), produced in 1960, which relied on [stimulated emission](https://bliptext.com/articles/stimulated-emission) of light from the chromium atoms in such a crystal.\nRuby has a laser transition at 694.3 nanometers, in a deep red color.\nChromium(VI) salts are used for the preservation of wood.\nFor example, [chromated copper arsenate](https://bliptext.com/articles/chromated-copper-arsenate) (CCA) is used in [timber treatment](https://bliptext.com/articles/timber-treatment) to protect wood from decay fungi, wood-attacking insects, including [termites](https://bliptext.com/articles/termites), and marine borers.\nThe formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%.\nIn the United States, 65,300 metric tons of CCA solution were used in 1996.\nChromium(III) salts, especially [chrome alum](https://bliptext.com/articles/chrome-alum) and [chromium(III) sulfate](https://bliptext.com/articles/chromium-iii-sulfate), are used in the tanning of [leather](https://bliptext.com/articles/leather).\nThe chromium(III) stabilizes the leather by cross linking the [collagen](https://bliptext.com/articles/collagen) fibers.\nChromium tanned leather can contain 4–5% of chromium, which is tightly bound to the proteins.\nAlthough the form of chromium used for tanning is not the toxic hexavalent variety, there remains interest in management of chromium in the tanning industry.\nRecovery and reuse, direct/indirect recycling, and \"chrome-less\" or \"chrome-free\" tanning are practiced to better manage chromium usage.\nThe high heat resistivity and high melting point makes [chromite](https://bliptext.com/articles/chromite) and chromium(III) oxide a material for high temperature refractory applications, like [blast furnaces](https://bliptext.com/articles/blast-furnace), cement [kilns](https://bliptext.com/articles/kiln), molds for the firing of [bricks](https://bliptext.com/articles/brick) and as foundry sands for the [casting](https://bliptext.com/articles/casting-metalworking) of metals.\nIn these applications, the refractory materials are made from mixtures of chromite and magnesite.\nThe use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).\nSeveral chromium compounds are used as [catalysts](https://bliptext.com/articles/catalyst) for processing hydrocarbons.\nFor example, the [Phillips catalyst](https://bliptext.com/articles/phillips-catalyst), prepared from chromium oxides, is used for the production of about half the world's [polyethylene](https://bliptext.com/articles/polyethylene).\nFe-Cr mixed oxides are employed as high-temperature catalysts for the [water gas shift reaction](https://bliptext.com/articles/water-gas-shift-reaction).\n[Copper chromite](https://bliptext.com/articles/copper-chromite) is a useful [hydrogenation](https://bliptext.com/articles/hydrogenation) catalyst.\n# [Red crystal of a ruby laser | upload.wikimedia.org/wikipedia/commons/7/7d/5///Maiman///Laser///Components.jpg]\n\n## Uses of compounds\n\n# Biological role\nThe possible nutritional value of chromium(III) is unproven.\nAlthough chromium is regarded as a trace element and [dietary mineral](https://bliptext.com/articles/mineral-nutrient), its suspected roles in the action of [insulin](https://bliptext.com/articles/insulin) – a hormone that mediates the metabolism and storage of carbohydrate, fat, and protein – have not been adequately established.\nThe [mechanism of its actions](https://bliptext.com/articles/mechanism-of-action) in the body is undefined, leaving in doubt whether chromium has a biological role in healthy people.\nIn contrast, [hexavalent chromium](https://bliptext.com/articles/hexavalent-chromium) (Cr(VI) or Cr6+) is highly toxic and [mutagenic](https://bliptext.com/articles/mutagen).\nIngestion of chromium(VI) in water has been linked to stomach tumors, and it may also cause allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis).\n\"[Chromium deficiency](https://bliptext.com/articles/chromium-deficiency)\", involving a lack of Cr(III) in the body, or perhaps some complex of it, such as [glucose tolerance factor](https://bliptext.com/articles/glucose-tolerance-factor), is not accepted as a medical condition, as it has no symptoms and healthy people do not require chromium supplementation.\nSome studies suggest that the biologically active form of chromium(III) is transported in the body via an oligopeptide called [low-molecular-weight chromium-binding substance](https://bliptext.com/articles/low-molecular-weight-chromium-binding-substance) (chromodulin), which might play a role in the insulin signaling pathway.\nThe chromium content of common foods is generally low (1–13 micrograms per serving).\nThe chromium content of food varies widely, due to differences in soil mineral content, growing season, plant [cultivar](https://bliptext.com/articles/cultivar), and contamination during processing.\nChromium (and [nickel](https://bliptext.com/articles/nickel)) leach into food cooked in stainless steel, with the effect being largest when the cookware is new.\nAcidic foods that are cooked for many hours also exacerbate this effect.\n\n## Dietary recommendations\nThere is disagreement on chromium's status as an essential nutrient.\nGovernmental departments from Australia, New Zealand, India, and Japan consider chromium as essential, while the United States and European Food Safety Authority of the European Union do not.\nThe U.S. [National Academy of Medicine](https://bliptext.com/articles/national-academy-of-medicine) (NAM) updated the [Estimated Average Requirements](https://bliptext.com/articles/dietary-reference-intake) (EARs) and the [Recommended Dietary Allowances](https://bliptext.com/articles/dietary-reference-intake) (RDAs) for chromium in 2001.\nFor chromium, there was insufficient information to set EARs and RDAs, so its needs are described as estimates for [Adequate Intake](https://bliptext.com/articles/dietary-reference-intake) (AI).\nFrom a 2001 assessment, AI of chromium for women ages 14 through 50 is 25 μg/day, and the AI for women ages 50 and above is 20 μg/day.\nThe AIs for women who are pregnant are 30 μg/day, and for women who are lactating, the set AI is 45 μg/day.\nThe AI for men ages 14 through 50 is 35 μg/day, and the AI for men ages 50 and above is 30 μg/day.\nFor children ages 1 through 13, the AI increases with age from 0.2 μg/day up to 25 μg/day.\nAs for safety, the NAM sets [Tolerable Upper Intake Levels](https://bliptext.com/articles/dietary-reference-intake) (ULs) for vitamins and minerals when the evidence is sufficient.\nIn the case of chromium, there is not yet enough information, hence no UL has been established.\nCollectively, the EARs, RDAs, AIs, and ULs are the parameters for the nutrition recommendation system known as [Dietary Reference Intake](https://bliptext.com/articles/dietary-reference-intake) (DRI).\nAustralia and New Zealand consider chromium to be an essential nutrient, with an AI of 35 μg/day for men, 25 μg/day for women, 30 μg/day for women who are pregnant, and 45 μg/day for women who are lactating.\nA UL has not been set due to the lack of sufficient data.\nIndia considers chromium to be an essential nutrient, with an adult recommended intake of 33 μg/day.\nJapan also considers chromium to be an essential nutrient, with an AI of 10 μg/day for adults, including women who are pregnant or lactating.\nA UL has not been set.\nThe EFSA does not consider chromium to be an essential nutrient.\n\n### Labeling\nFor U.S. food and dietary supplement labeling purposes, the amount of the substance in a serving is expressed as a percent of the [Daily Value](https://bliptext.com/articles/reference-daily-intake) (%DV).\nFor chromium labeling purposes, 100% of the Daily Value was 120 μg. As of 27 May 2016, the percentage of daily value was revised to 35 μg to bring the chromium intake into a consensus with the official [Recommended Dietary Allowance](https://bliptext.com/articles/dietary-reference-intake).\nA table of the old and new adult daily values in the United States is provided at [Reference Daily Intake](https://bliptext.com/articles/reference-daily-intake).\nAfter evaluation of research on the potential nutritional value of chromium, the European Food Safety Authority concluded that there was no evidence of benefit by dietary chromium in healthy people, thereby declining to establish recommendations in Europe for dietary intake of chromium.\n\n## Food sources\nFood composition databases such as those maintained by the U.S. Department of Agriculture do not contain information on the chromium content of foods.\nA wide variety of animal and vegetable foods contain chromium.\nContent per serving is influenced by the chromium content of the soil in which the plants are grown, by foodstuffs fed to animals, and by processing methods, as chromium is leached into foods if processed or cooked in stainless steel equipment.\nOne diet analysis study conducted in Mexico reported an average daily chromium intake of 30 micrograms.\nAn estimated 31% of adults in the United States consume multi-vitamin/mineral dietary supplements, which often contain 25 to 60 micrograms of chromium.\n\n## Supplementation\nChromium is an ingredient in [total parenteral nutrition](https://bliptext.com/articles/total-parenteral-nutrition) (TPN), because deficiency can occur after months of intravenous feeding with chromium-free TPN.\nIt is also added to nutritional products for [preterm infants](https://bliptext.com/articles/preterm-infant).\nAlthough the mechanism of action in biological roles for chromium is unclear, in the United States chromium-containing products are sold as non-prescription dietary supplements in amounts ranging from 50 to 1,000 μg. Lower amounts of chromium are also often incorporated into multi-vitamin/mineral supplements consumed by an estimated 31% of adults in the United States.\nChemical compounds used in dietary supplements include chromium chloride, chromium citrate, [chromium(III) picolinate](https://bliptext.com/articles/chromium-iii-picolinate), [chromium(III) polynicotinate](https://bliptext.com/articles/chromium-polynicotinate), and other chemical compositions.\nThe benefit of supplements has not been proven.\n\n### Initiation of research on glucose\nThe notion of chromium as a potential regulator of glucose metabolism began in the 1950s when scientists performed a series of experiments controlling the diet of rats.\nThe experimenters subjected the rats to a chromium deficient diet, and witnessed an inability to respond effectively to increased levels of blood glucose.\nA chromium-rich [Brewer's yeast](https://bliptext.com/articles/yeast) was provided in the diet, enabling the rats to effectively metabolize glucose, and so giving evidence that chromium may have a role in glucose management.\n\n## Approved and disapproved health claims\nIn 2005, the U.S. Food and Drug Administration had approved a qualified health claim for chromium picolinate with a requirement for specific label wording:\nIn other parts of the petition, the FDA rejected claims for chromium picolinate and cardiovascular disease, retinopathy or kidney disease caused by abnormally high blood sugar levels.\nAs of March 2024, this ruling on chromium remains in effect.\nIn 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements.\nApproved labeling statements include: a factor in the maintenance of good health, provides support for healthy glucose metabolism, helps the body to metabolize carbohydrates and helps the body to metabolize fats.\nThe European Food Safety Authority approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration, but rejected claims for maintenance or achievement of a normal body weight, or reduction of tiredness or fatigue.\nHowever, in a 2014 reassessment of studies to determine whether a Dietary Reference Intake value could be established for chromium, EFSA stated:\n\n### Diabetes\nGiven the evidence for chromium deficiency causing problems with glucose management in the context of intravenous nutrition products formulated without chromium, research interest turned to whether chromium supplementation would benefit people who have type 2 diabetes but are not chromium deficient.\nLooking at the results from four meta-analyses, one reported a statistically significant decrease in fasting [plasma glucose](https://bliptext.com/articles/plasma-glucose) levels and a non-significant trend in lower [hemoglobin A1C](https://bliptext.com/articles/glycated-hemoglobin).\nA second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either.\nA review published in 2016 listed 53 [randomized clinical trials](https://bliptext.com/articles/randomized-clinical-trial) that were included in one or more of six [meta-analyses](https://bliptext.com/articles/meta-analysis).\nIt concluded that whereas there may be modest decreases in fasting blood glucose and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome.\n\n### Body weight\nTwo [systematic reviews](https://bliptext.com/articles/systematic-review) looked at chromium supplements as a mean of managing body weight in overweight and obese people.\nOne, limited to [chromium picolinate](https://bliptext.com/articles/chromium-picolinate), a common supplement ingredient, reported a statistically significant −1.1 kg (2.4 lb) weight loss in trials longer than 12 weeks.\nThe other included all chromium compounds and reported a statistically significant −0.50 kg (1.1 lb) weight change.\nChange in percent body fat did not reach statistical significance.\nAuthors of both reviews considered the clinical relevance of this modest weight loss as uncertain/unreliable.\nThe European Food Safety Authority reviewed the literature and concluded that there was insufficient evidence to support a claim.\n\n### Sports\nChromium is promoted as a sports performance dietary supplement, based on the theory that it potentiates insulin activity, with anticipated results of increased muscle mass, and faster recovery of glycogen storage during post-exercise recovery.\nA review of clinical trials reported that chromium supplementation did not improve exercise performance or increase muscle strength.\nThe International Olympic Committee reviewed dietary supplements for high-performance athletes in 2018 and concluded there was no need to increase chromium intake for athletes, nor support for claims of losing body fat.\n\n## Fresh-water fish\nIrrigation water standards for chromium are 0.1 mg/L, but some rivers in [Bangladesh](https://bliptext.com/articles/bangladesh) are more than five times that amount.\nThe standard for fish for human consumption is less than 1 mg/kg, but many tested samples were more than five times that amount.\nChromium, especially hexavalent chromium, is highly toxic to fish because it is easily absorbed across the gills, readily enters blood circulation, crosses cell membranes and bioconcentrates up the food chain.\nIn contrast, the toxicity of trivalent chromium is very low, attributed to poor membrane permeability and little biomagnification.\nAcute and chronic exposure to chromium(VI) affects fish behavior, physiology, reproduction and survival.\nHyperactivity and erratic swimming have been reported in contaminated environments.\nEgg hatching and fingerling survival are affected.\nIn adult fish there are reports of histopathological damage to liver, kidney, muscle, intestines, and gills.\nMechanisms include mutagenic gene damage and disruptions of enzyme functions.\nThere is evidence that fish may not require chromium, but benefit from a measured amount in diet.\nIn one study, juvenile fish gained weight on a zero chromium diet, but the addition of 500 μg of chromium in the form of chromium chloride or other supplement types, per kilogram of food (dry weight), increased weight gain.\nAt 2,000 μg/kg the weight gain was no better than with the zero chromium diet, and there were increased DNA strand breaks.\n\n# Precautions\nWater-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.\nBecause of the specific [transport](https://bliptext.com/articles/transport-protein) mechanisms, only limited amounts of chromium(III) enter the cells.\nAcute oral toxicity ranges between 50 and 150 mg/kg.\nA 2008 review suggested that moderate uptake of chromium(III) through dietary supplements poses no genetic-toxic risk.\nIn the US, the [Occupational Safety and Health Administration](https://bliptext.com/articles/occupational-safety-and-health-administration) (OSHA) has designated an air [permissible exposure limit](https://bliptext.com/articles/permissible-exposure-limit) (PEL) in the workplace as a time-weighted average (TWA) of 1 mg/m3.\nThe [National Institute for Occupational Safety and Health](https://bliptext.com/articles/national-institute-for-occupational-safety-and-health) (NIOSH) has set a [recommended exposure limit](https://bliptext.com/articles/recommended-exposure-limit) (REL) of 0.5 mg/m3, time-weighted average.\nThe [IDLH](https://bliptext.com/articles/idlh) (immediately dangerous to life and health) value is 250 mg/m3.\n\n## Chromium(VI) toxicity\nThe acute [oral](https://bliptext.com/articles/mouth) [toxicity](https://bliptext.com/articles/toxicity) for [chromium(VI)](https://bliptext.com/articles/hexavalent-chromium) ranges between 1.5 and 3.3 mg/kg.\nIn the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells.\nThe chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also [sulfate](https://bliptext.com/articles/sulfate) and [phosphate](https://bliptext.com/articles/phosphate) ions enter the cell.\nThe acute toxicity of chromium(VI) is due to its strong [oxidant](https://bliptext.com/articles/redox) properties.\nAfter it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions.\n[Hemolysis](https://bliptext.com/articles/hemolysis), [renal](https://bliptext.com/articles/renal), and liver failure result.\nAggressive dialysis can be therapeutic.\nThe [carcinogenity](https://bliptext.com/articles/carcinogenity) of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.\nThree mechanisms have been proposed to describe the [genotoxicity](https://bliptext.com/articles/genotoxicity) of chromium(VI).\nThe first mechanism includes highly reactive [hydroxyl radicals](https://bliptext.com/articles/hydroxyl-radical) and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III).\nThe second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the [DNA](https://bliptext.com/articles/dna).\nThe last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.\nChromium salts (chromates) are also the cause of [allergic reactions](https://bliptext.com/articles/allergic-reaction) in some people.\nChromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.\nContact with products containing chromates can lead to allergic [contact dermatitis](https://bliptext.com/articles/contact-dermatitis) and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as \"chrome ulcers\".\nThis condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.\n\n## Environmental issues\nBecause chromium compounds were used in [dyes](https://bliptext.com/articles/dye), [paints](https://bliptext.com/articles/paint), and [leather](https://bliptext.com/articles/leather) [tanning](https://bliptext.com/articles/tanning-leather) compounds, these compounds are often found in soil and [groundwater](https://bliptext.com/articles/groundwater) at active and abandoned industrial sites, needing [environmental cleanup](https://bliptext.com/articles/environmental-cleanup) and [remediation](https://bliptext.com/articles/environmental-remediation).\n[Primer paint](https://bliptext.com/articles/primer-paint) containing hexavalent chromium is still widely used for [aerospace](https://bliptext.com/articles/aerospace) and [automobile](https://bliptext.com/articles/automobile) refinishing applications.\nIn 2010, the [Environmental Working Group](https://bliptext.com/articles/environmental-working-group) studied the drinking water in 35 American cities in the first nationwide study.\nThe study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with [Norman, Oklahoma](https://bliptext.com/articles/norman-oklahoma), at the top of list; 25 cities had levels that exceeded California's proposed limit.\nThe more toxic hexavalent chromium form can be reduced to the less soluble trivalent oxidation state in soils by organic matter, ferrous iron, sulfides, and other reducing agents, with the rates of such reduction being faster under more acidic conditions than under more alkaline ones.\nIn contrast, trivalent chromium can be oxidized to hexavalent chromium in soils by manganese oxides, such as Mn(III) and Mn(IV) compounds.\nSince the solubility and toxicity of chromium (VI) are greater that those of chromium (III), the oxidation-reduction conversions between the two oxidation states have implications for movement and bioavailability of chromium in soils, groundwater, and plants.\n\n# General bibliography","revisionCount":3},"hasMore":false,"nextCursor":null}