{"history":[],"article":{"id":"a3ff8f6a-5b02-48d3-bb00-9d16700f0b19","title":"Zirconium hydride","slug":"zirconium-hydride","content":":::summary\n:::\n\n# \n**Zirconium hydride** describes an [alloy](https://bliptext.com/articles/alloy) made by combining [zirconium](https://bliptext.com/articles/zirconium) and [hydrogen](https://bliptext.com/articles/hydrogen).\nHydrogen acts as a hardening agent, preventing [dislocations](https://bliptext.com/articles/dislocation) in the zirconium atom [crystal lattice](https://bliptext.com/articles/crystal-lattice) from sliding past one another.\nVarying the amount of hydrogen and the form of its presence in the zirconium hydride (precipitated phase) controls qualities such as the [hardness](https://bliptext.com/articles/hardness-materials-science), [ductility](https://bliptext.com/articles/ductility), and [tensile strength](https://bliptext.com/articles/ultimate-tensile-strength) of the resulting zirconium hydride.\nZirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.\n\n# Material properties\nZirconium is found in the [Earth](https://bliptext.com/articles/earth)'s [crust](https://bliptext.com/articles/crust-geology) only in the form of an [ore](https://bliptext.com/articles/ore), usually a [zircon](https://bliptext.com/articles/zircon)ium silicate, such as [zircon](https://bliptext.com/articles/zircon).\nZirconium is extracted from zirconium ore by removing the oxygen and silica.\nThis process, known as the [Kroll process](https://bliptext.com/articles/kroll-process), was first applied to [titanium](https://bliptext.com/articles/titanium).\nThe Kroll process results in an alloy containing [hafnium](https://bliptext.com/articles/hafnium).\nThe hafnium and other impurities are removed in a subsequent step.\nZirconium hydride is created by combining refined zirconium with hydrogen.\nLike titanium, solid zirconium dissolves hydrogen quite readily.\nThe [density](https://bliptext.com/articles/density) of zirconium hydride varies based the hydrogen and ranges between 5.56 and 6.52 g cm−3.\nEven in the narrow range of concentrations which make up zirconium hydride, mixtures of hydrogen and zirconium can form a number of different structures, with very different properties.\nUnderstanding such properties is essential to making quality zirconium hydride.\nAt [room temperature](https://bliptext.com/articles/room-temperature), the most stable form of zirconium is the [hexagonal close-packed](https://bliptext.com/articles/close-packing-of-equal-spheres) (HCP) structure α-zirconium.\nIt is a fairly soft metallic material that can dissolve only a small concentration of hydrogen, no more than 0.069 wt% at 550 °C.\nIf zirconium hydride contains more than 0.069% hydrogen at zirconium hydride making temperatures then it transforms into a [body-centred cubic](https://bliptext.com/articles/cubic-crystal-system) (BCC) structure called β-zirconium.\nIt can dissolve considerably more hydrogen, more than 1.2% hydrogen above 900 °C.\nWhen zirconium hydrides with less than 0.7% hydrogen, known as hypoeutectoid zirconium hydride, are cooled from the β phase the mixture attempts to revert to the α phase, resulting in an excess of hydrogen.\nAnother [polymorphic form](https://bliptext.com/articles/polymorphism-materials-science) is the γ phase, is generally accepted to be a metastable phase.\nZirconium hydrides are odorless, dark gray to black metallic powders.\nThey behave as usual metals in terms of electrical conductivity and magnetic properties ([paramagnetic](https://bliptext.com/articles/paramagnetism), unless contaminated with [ferromagnetic](https://bliptext.com/articles/ferromagnetism) impurities).\nTheir structure and composition is stable at ambient conditions.\nSimilar to other metal hydrides, different crystalline phases of zirconium hydrides are conventionally labeled with Greek letters, and α is reserved for the metal.\nThe known ZrHx phases are γ (x = 1), δ (x = 1.5–1.65) and ε (x = 1.75–2).\nFractional x values often correspond to mixtures, so the compositions with x = 0.8–1.5 usually contain a mixture of α, γ and δ phases, and δ and ε phases coexist for x = 1.65–1.75.\nAs a function of increasing x, the transition between δ-Zr and ε-Zr is observed as a gradual distortion of the [face-centered cubic](https://bliptext.com/articles/cubic-crystal-system) δ ([fluorite](https://bliptext.com/articles/fluorite)-type) to face-centered tetragonal ε lattice.\nThis distortion is accompanied by a rapid decrease in [Vickers hardness](https://bliptext.com/articles/vickers-hardness), which is constant at 260 HV for x < 1.6, linearly decreases to 160 HV for 1.6 < x < 1.75 and stabilizes at about 160 HV for 1.75 < x < 2.0.\nThis hardness decrease is accompanied by the decrease in [magnetic susceptibility](https://bliptext.com/articles/magnetic-susceptibility).\nThe mass density behaves differently with the increasing hydrogen content: it decreases linearly from 6.52 to 5.66 g/cm3 for x = 0–1.6 and changes little for x = 1.6–2.0.\n\n# Preparation and chemical properties\nZirconium hydrides form upon interaction of the metal with hydrogen gas.\nWhereas this reaction occurs even at room temperature, homogeneous bulk hydrogenation is usually achieved by annealing at temperatures of 400–600 °C for a period between several hours and a few weeks.\nAt room temperature, zirconium hydrides quickly oxidize in air, and even in high vacuum.\nThe formed nanometer-thin layer of oxide stops further oxygen diffusion into the material, and thus the change in composition due to oxidation can usually be neglected.\nHowever, the oxidation proceeds deeper into the bulk with increasing temperature.\nThe hydrogen is anionic due to the electronegativity difference between Zr and H. When prepared as thin films, the crystal structure can be improved and surface oxidation minimized.\nZirconium hydrides are soluble in [hydrofluoric acid](https://bliptext.com/articles/hydrofluoric-acid) or alcohol; they react violently with water, acids, oxidizers or halogenated compounds.\n\n# Applications\nFormation of zirconium hydrides is an important factor in the operation of several types of [nuclear reactors](https://bliptext.com/articles/nuclear-reactors), such as [boiling water reactors](https://bliptext.com/articles/boiling-water-reactor) [Fukushima I](https://bliptext.com/articles/fukushima-i-nuclear-power-plant) and [II](https://bliptext.com/articles/fukushima-ii-nuclear-power-plant), which suffered from a series of [explosions](https://bliptext.com/articles/fukushima-i-nuclear-accidents) caused by the [2011 Tōhoku earthquake and tsunami](https://bliptext.com/articles/2011-t-hoku-earthquake-and-tsunami).\nTheir [uranium](https://bliptext.com/articles/uranium) [fuel pellets](https://bliptext.com/articles/nuclear-fuel) are enclosed in metal rods made from [Zircaloy](https://bliptext.com/articles/zircaloy) – an alloy of typically about 98.25% zirconium with 1.5% tin and minor amounts of other metals.\nZircaloy is used because of its small absorption cross-section for thermal neutrons and superior mechanical and corrosion properties to those of most metals, including zirconium.\nThe rods are cooled by streaming water which gradually oxidizes zirconium, liberating hydrogen.\nIn Fukushima reactors, the reactor cooling system failed because of the tsunami.\nThe resulting temperature increase accelerated chemical reactions and caused accumulation of significant amounts of hydrogen, which exploded upon reaction with oxygen when the gas was released to the atmosphere.\nIn regular operation, most hydrogen is safely neutralized in the reactor systems; however, a fraction of 5-20% diffuses into the Zircaloy rods forming zirconium hydrides.\nThis process mechanically weakens the rods because the hydrides have lower hardness and ductility than metal.\nOnly a few percent of hydrogen can dissolve in zirconium.\nExcess hydrogen forms voids that weaken Zircalloy.\nAmong Zircaloys, Zircaloy-4 is the least susceptible to hydrogen blistering.\nIt is also used as a [neutron moderator](https://bliptext.com/articles/neutron-moderator) in [thermal-spectrum](https://bliptext.com/articles/neutron-temperature) [nuclear reactors](https://bliptext.com/articles/nuclear-reactor) such as the [TRIGA](https://bliptext.com/articles/triga) research reactor developed by [General Atomics](https://bliptext.com/articles/general-atomics) or the Soviet TOPAZ [nuclear reactors](https://bliptext.com/articles/nuclear-reactor).\nAt neutron energies above 0.14 eV it is as effective at moderating a nuclear reactor as elemental hydrogen (the best known material), but far more dense, and therefore permits compact reactors with high power per unit volume.\nIt has neutron resonances that prevent almost all moderation at energies below 0.14 eV.\nZirconium deuteride is superior, because it has a lower neutron absorption cross-section than aneutronic hydrogen, decreasing neutron absorption in a reactor.\nAs a pure powder, zirconium hydrides are used as hydrogenation catalysts, in powder metallurgy, and as getters in the vacuum tube industry.\nIn vacuum systems, zirconium hydrides help establish a seal between a metal and ceramic.\nIn this method, a hydride powder is mixed with the sealing metal; heating the mixture results in decomposition of the hydride.\nThe evolving hydrogen cleans up the surrounding area, and the produced metal flows and forms a seal even at temperatures as low as 300 °C.\nZrH2 is used in [powder metallurgy](https://bliptext.com/articles/powder-metallurgy), as a [hydrogenation](https://bliptext.com/articles/hydrogenation) [catalyst](https://bliptext.com/articles/catalyst), and as a [reducing agent](https://bliptext.com/articles/reducing-agent), [vacuum tube](https://bliptext.com/articles/vacuum-tube) [getter](https://bliptext.com/articles/getter), and a [foaming agent](https://bliptext.com/articles/foaming-agent) in production of [metal foams](https://bliptext.com/articles/metal-foam).\nOther uses include acting as a fuel in [pyrotechnic compositions](https://bliptext.com/articles/pyrotechnic-composition), namely [pyrotechnic initiators](https://bliptext.com/articles/pyrotechnic-initiator).\n\n# Safety\nPowdered zirconium hydrides are flammable and can ignite and explode if exposed to heat, fire, or sparks.\nWhen heated above 300 °C, they decompose releasing hydrogen gas, which is also flammable.","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-26T06:52:23.379Z","updated_at":"2025-01-26T06:52:23.379Z","search_vector":"'hydrid':2 'zirconium':1","search_content":" \n \n\n# \n**Zirconium hydride** describes an [alloy](https://bliptext.com/articles/alloy) made by combining [zirconium](https://bliptext.com/articles/zirconium) and [hydrogen](https://bliptext.com/articles/hydrogen).\nHydrogen acts as a hardening agent, preventing [dislocations](https://bliptext.com/articles/dislocation) in the zirconium atom [crystal lattice](https://bliptext.com/articles/crystal-lattice) from sliding past one another.\nVarying the amount of hydrogen and the form of its presence in the zirconium hydride (precipitated phase) controls qualities such as the [hardness](https://bliptext.com/articles/hardness-materials-science), [ductility](https://bliptext.com/articles/ductility), and [tensile strength](https://bliptext.com/articles/ultimate-tensile-strength) of the resulting zirconium hydride.\nZirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.\n\n# Material properties\nZirconium is found in the [Earth](https://bliptext.com/articles/earth)'s [crust](https://bliptext.com/articles/crust-geology) only in the form of an [ore](https://bliptext.com/articles/ore), usually a [zircon](https://bliptext.com/articles/zircon)ium silicate, such as [zircon](https://bliptext.com/articles/zircon).\nZirconium is extracted from zirconium ore by removing the oxygen and silica.\nThis process, known as the [Kroll process](https://bliptext.com/articles/kroll-process), was first applied to [titanium](https://bliptext.com/articles/titanium).\nThe Kroll process results in an alloy containing [hafnium](https://bliptext.com/articles/hafnium).\nThe hafnium and other impurities are removed in a subsequent step.\nZirconium hydride is created by combining refined zirconium with hydrogen.\nLike titanium, solid zirconium dissolves hydrogen quite readily.\nThe [density](https://bliptext.com/articles/density) of zirconium hydride varies based the hydrogen and ranges between 5.56 and 6.52 g cm−3.\nEven in the narrow range of concentrations which make up zirconium hydride, mixtures of hydrogen and zirconium can form a number of different structures, with very different properties.\nUnderstanding such properties is essential to making quality zirconium hydride.\nAt [room temperature](https://bliptext.com/articles/room-temperature), the most stable form of zirconium is the [hexagonal close-packed](https://bliptext.com/articles/close-packing-of-equal-spheres) (HCP) structure α-zirconium.\nIt is a fairly soft metallic material that can dissolve only a small concentration of hydrogen, no more than 0.069 wt% at 550 °C.\nIf zirconium hydride contains more than 0.069% hydrogen at zirconium hydride making temperatures then it transforms into a [body-centred cubic](https://bliptext.com/articles/cubic-crystal-system) (BCC) structure called β-zirconium.\nIt can dissolve considerably more hydrogen, more than 1.2% hydrogen above 900 °C.\nWhen zirconium hydrides with less than 0.7% hydrogen, known as hypoeutectoid zirconium hydride, are cooled from the β phase the mixture attempts to revert to the α phase, resulting in an excess of hydrogen.\nAnother [polymorphic form](https://bliptext.com/articles/polymorphism-materials-science) is the γ phase, is generally accepted to be a metastable phase.\nZirconium hydrides are odorless, dark gray to black metallic powders.\nThey behave as usual metals in terms of electrical conductivity and magnetic properties ([paramagnetic](https://bliptext.com/articles/paramagnetism), unless contaminated with [ferromagnetic](https://bliptext.com/articles/ferromagnetism) impurities).\nTheir structure and composition is stable at ambient conditions.\nSimilar to other metal hydrides, different crystalline phases of zirconium hydrides are conventionally labeled with Greek letters, and α is reserved for the metal.\nThe known ZrHx phases are γ (x = 1), δ (x = 1.5–1.65) and ε (x = 1.75–2).\nFractional x values often correspond to mixtures, so the compositions with x = 0.8–1.5 usually contain a mixture of α, γ and δ phases, and δ and ε phases coexist for x = 1.65–1.75.\nAs a function of increasing x, the transition between δ-Zr and ε-Zr is observed as a gradual distortion of the [face-centered cubic](https://bliptext.com/articles/cubic-crystal-system) δ ([fluorite](https://bliptext.com/articles/fluorite)-type) to face-centered tetragonal ε lattice.\nThis distortion is accompanied by a rapid decrease in [Vickers hardness](https://bliptext.com/articles/vickers-hardness), which is constant at 260 HV for x < 1.6, linearly decreases to 160 HV for 1.6 < x < 1.75 and stabilizes at about 160 HV for 1.75 < x < 2.0.\nThis hardness decrease is accompanied by the decrease in [magnetic susceptibility](https://bliptext.com/articles/magnetic-susceptibility).\nThe mass density behaves differently with the increasing hydrogen content: it decreases linearly from 6.52 to 5.66 g/cm3 for x = 0–1.6 and changes little for x = 1.6–2.0.\n\n# Preparation and chemical properties\nZirconium hydrides form upon interaction of the metal with hydrogen gas.\nWhereas this reaction occurs even at room temperature, homogeneous bulk hydrogenation is usually achieved by annealing at temperatures of 400–600 °C for a period between several hours and a few weeks.\nAt room temperature, zirconium hydrides quickly oxidize in air, and even in high vacuum.\nThe formed nanometer-thin layer of oxide stops further oxygen diffusion into the material, and thus the change in composition due to oxidation can usually be neglected.\nHowever, the oxidation proceeds deeper into the bulk with increasing temperature.\nThe hydrogen is anionic due to the electronegativity difference between Zr and H. When prepared as thin films, the crystal structure can be improved and surface oxidation minimized.\nZirconium hydrides are soluble in [hydrofluoric acid](https://bliptext.com/articles/hydrofluoric-acid) or alcohol; they react violently with water, acids, oxidizers or halogenated compounds.\n\n# Applications\nFormation of zirconium hydrides is an important factor in the operation of several types of [nuclear reactors](https://bliptext.com/articles/nuclear-reactors), such as [boiling water reactors](https://bliptext.com/articles/boiling-water-reactor) [Fukushima I](https://bliptext.com/articles/fukushima-i-nuclear-power-plant) and [II](https://bliptext.com/articles/fukushima-ii-nuclear-power-plant), which suffered from a series of [explosions](https://bliptext.com/articles/fukushima-i-nuclear-accidents) caused by the [2011 Tōhoku earthquake and tsunami](https://bliptext.com/articles/2011-t-hoku-earthquake-and-tsunami).\nTheir [uranium](https://bliptext.com/articles/uranium) [fuel pellets](https://bliptext.com/articles/nuclear-fuel) are enclosed in metal rods made from [Zircaloy](https://bliptext.com/articles/zircaloy) – an alloy of typically about 98.25% zirconium with 1.5% tin and minor amounts of other metals.\nZircaloy is used because of its small absorption cross-section for thermal neutrons and superior mechanical and corrosion properties to those of most metals, including zirconium.\nThe rods are cooled by streaming water which gradually oxidizes zirconium, liberating hydrogen.\nIn Fukushima reactors, the reactor cooling system failed because of the tsunami.\nThe resulting temperature increase accelerated chemical reactions and caused accumulation of significant amounts of hydrogen, which exploded upon reaction with oxygen when the gas was released to the atmosphere.\nIn regular operation, most hydrogen is safely neutralized in the reactor systems; however, a fraction of 5-20% diffuses into the Zircaloy rods forming zirconium hydrides.\nThis process mechanically weakens the rods because the hydrides have lower hardness and ductility than metal.\nOnly a few percent of hydrogen can dissolve in zirconium.\nExcess hydrogen forms voids that weaken Zircalloy.\nAmong Zircaloys, Zircaloy-4 is the least susceptible to hydrogen blistering.\nIt is also used as a [neutron moderator](https://bliptext.com/articles/neutron-moderator) in [thermal-spectrum](https://bliptext.com/articles/neutron-temperature) [nuclear reactors](https://bliptext.com/articles/nuclear-reactor) such as the [TRIGA](https://bliptext.com/articles/triga) research reactor developed by [General Atomics](https://bliptext.com/articles/general-atomics) or the Soviet TOPAZ [nuclear reactors](https://bliptext.com/articles/nuclear-reactor).\nAt neutron energies above 0.14 eV it is as effective at moderating a nuclear reactor as elemental hydrogen (the best known material), but far more dense, and therefore permits compact reactors with high power per unit volume.\nIt has neutron resonances that prevent almost all moderation at energies below 0.14 eV.\nZirconium deuteride is superior, because it has a lower neutron absorption cross-section than aneutronic hydrogen, decreasing neutron absorption in a reactor.\nAs a pure powder, zirconium hydrides are used as hydrogenation catalysts, in powder metallurgy, and as getters in the vacuum tube industry.\nIn vacuum systems, zirconium hydrides help establish a seal between a metal and ceramic.\nIn this method, a hydride powder is mixed with the sealing metal; heating the mixture results in decomposition of the hydride.\nThe evolving hydrogen cleans up the surrounding area, and the produced metal flows and forms a seal even at temperatures as low as 300 °C.\nZrH2 is used in [powder metallurgy](https://bliptext.com/articles/powder-metallurgy), as a [hydrogenation](https://bliptext.com/articles/hydrogenation) [catalyst](https://bliptext.com/articles/catalyst), and as a [reducing agent](https://bliptext.com/articles/reducing-agent), [vacuum tube](https://bliptext.com/articles/vacuum-tube) [getter](https://bliptext.com/articles/getter), and a [foaming agent](https://bliptext.com/articles/foaming-agent) in production of [metal foams](https://bliptext.com/articles/metal-foam).\nOther uses include acting as a fuel in [pyrotechnic compositions](https://bliptext.com/articles/pyrotechnic-composition), namely [pyrotechnic initiators](https://bliptext.com/articles/pyrotechnic-initiator).\n\n# Safety\nPowdered zirconium hydrides are flammable and can ignite and explode if exposed to heat, fire, or sparks.\nWhen heated above 300 °C, they decompose releasing hydrogen gas, which is also flammable.","revisionCount":0},"hasMore":false,"nextCursor":null}

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