Titanium hydride

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Titanium hydride
Titanium hydride TiH2.jpg
Titanium hydride powder
Names
IUPAC name
titanium dihydride (hydrogen deficient)
Identifiers
ECHA InfoCard 100.028.843 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
Properties
TiH2−x
Molar mass 49.88 g/mol (TiH2)
Appearanceblack powder (commercial form)
Density 3.76 g/cm3 (typical commercial form)
Melting point Decomposes
insoluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Titanium hydride normally refers to the inorganic compound TiH2 and related nonstoichiometric materials. [1] [2] It is commercially available as a stable grey/black powder, which is used as an additive in the production of Alnico sintered magnets, in the sintering of powdered metals, the production of metal foam, the production of powdered titanium metal and in pyrotechnics. [3]

Contents

Also known as titanium–hydrogen alloy, [4] [5] it is an alloy [6] of titanium, hydrogen, and possibly other elements. When hydrogen is the main alloying element, its content in the titanium hydride is between 0.02% and 4.0% by weight. Alloying elements intentionally added to modify the characteristics of titanium hydride include gallium, iron, vanadium, and aluminium.

Production

In the commercial process for producing non-stoichiometric TiH2−x, titanium metal sponge is treated with hydrogen gas at atmospheric pressure at between 300-500 °C. Absorption of hydrogen is exothermic and rapid, changing the color of the sponge grey/black. The brittle product is ground to a powder, which has a composition around TiH1.95. [3] In the laboratory, titanium hydride is produced by heating titanium powder under flowing hydrogen at 700 °C, the idealized equation being: [7]

Ti + H2 → TiH2

Other methods of producing titanium hydride include electrochemical and ball milling methods. [8] [9]

Reactions

TiH1.95 is unaffected by water and air.[ citation needed ] It is slowly attacked by strong acids and is degraded by hydrofluoric and hot sulfuric acids. It reacts rapidly with oxidizing agents, this reactivity leading to the use of titanium hydride in pyrotechnics. [3]

The material has been used to produce highly pure hydrogen, which is released upon heating the solid. [7] Hydrogen release in TiH~2 starts just above 400 °C but may not be complete until the melting point of titanium metal. [10] [3] Titanium tritide (Ti3Hx) has been proposed for long-term storage of tritium gas. [11]

Structure

As TiHx approaches stoichiometry, it adopts a distorted body-centered tetragonal structure, termed the ε-form with an axial ratio of less than 1. This composition is very unstable with respect to partial thermal decomposition, unless maintained under a pure hydrogen atmosphere. Otherwise, the composition rapidly decomposes at room temperature until an approximate composition of TiH1.74 is reached.[ citation needed ] This composition adopts the fluorite structure, and is termed the δ-form, and only very slowly thermally decomposing at room temperature until an approximate composition of TiH1.47 is reached, at which point, inclusions of the hexagonal close packed α-form, which is the same form as pure titanium, begin to appear.

The evolution of the dihydride from titanium metal and hydrogen has been examined in some detail. α-Titanium has a hexagonal close packed (hcp) structure at room temperature. Hydrogen initially occupies tetrahedral interstitial sites in the titanium. As the H/Ti ratio approaches 2, the material adopts the β-form to a face centred cubic (fcc), δ-form, the H atoms eventually filling all the tetrahedral sites to give the limiting stoichiometry of TiH2. The various phases are described in the table below.

Temperature approx. 500 °C, taken from illustration [12]
PhaseWeight % HAtomic % HTiHxMetal lattice
α0 – 0.20 – 8TiH0 – TiH0.1 hcp
α & β0.2 – 1.18 – 34TiH0.1 – TiH0.5
β1.1 – 1.834 – 47TiH0.5 – TiH0.9 bcc
β & δ1.8 – 2.547 – 57TiH0.9 – TiH1.32
δ2.7 – 4.157 – 67TiH1.32 – TiH2 fcc

If titanium hydride contains 4.0% hydrogen at less than around 40 °C then it transforms into a body-centred tetragonal (bct) structure called ε-titanium. [12]

When titanium hydrides with less than 1.3% hydrogen, known as hypoeutectoid titanium hydride are cooled, the β-titanium phase of the mixture attempts to revert to the α-titanium phase, resulting in an excess of hydrogen. One way for hydrogen to leave the β-titanium phase is for the titanium to partially transform into δ-titanium, leaving behind titanium that is low enough in hydrogen to take the form of α-titanium, resulting in an α-titanium matrix with δ-titanium inclusions.

A metastable γ-titanium hydride phase has been reported. [13] When α-titanium hydride with a hydrogen content of 0.02-0.06% is quenched rapidly, it forms into γ-titanium hydride, as the atoms "freeze" in place when the cell structure changes from hcp to fcc. γ-Titanium takes a body centred tetragonal (bct) structure. Moreover, there is no compositional change so the atoms generally retain their same neighbours.

Hydrogen embrittlement in titanium and titanium alloys

Selected colours achievable through anodization of titanium. Anodized titanium colors.svg
Selected colours achievable through anodization of titanium.

The absorption of hydrogen and the formation of titanium hydride are a source of damage to titanium and titanium alloys. This hydrogen embrittlement process is of particular concern when titanium and alloys are used as structural materials, as in nuclear reactors.

Hydrogen embrittlement manifests as a reduction in ductility and eventually spalling of titanium surfaces. The effect of hydrogen is to a large extent determined by the composition, metallurgical history and handling of the Ti and Ti alloy. [14] CP-titanium (commercially pure: ≤99.55% Ti content) is more susceptible to hydrogen attack than pure α-titanium. Embrittlement, observed as a reduction in ductility and caused by the formation of a solid solution of hydrogen, can occur in CP-titanium at concentrations as low as 30-40 ppm. Hydride formation has been linked to the presence of iron in the surface of a Ti alloy. Hydride particles are observed in specimens of Ti and Ti alloys that have been welded, and because of this welding is often carried out under an inert gas shield to reduce the possibility of hydride formation. [14]

Ti and Ti alloys form a surface oxide layer, composed of a mixture of Ti(II), Ti(III) and Ti(IV) oxides, [15] which offers a degree of protection to hydrogen entering the bulk. [14] The thickness of this can be increased by anodizing, a process which also results in a distinctive colouration of the material. Ti and Ti alloys are often used in hydrogen containing environments and in conditions where hydrogen is reduced electrolytically on the surface. Pickling, an acid bath treatment which is used to clean the surface can be a source of hydrogen.

Uses

Common applications include ceramics, pyrotechnics, sports equipment, as a laboratory reagent, as a blowing agent, and as a precursor to porous titanium. When heated as a mixture with other metals in powder metallurgy, titanium hydride releases hydrogen which serves to remove carbon and oxygen, producing a strong alloy. [3]


The density of titanium hydride varies based on the alloying constituents, but for pure titanium hydride it ranges between 3.76 and 4.51 g/cm3.

Even in the narrow range of concentrations that make up titanium hydride, mixtures of hydrogen and titanium can form a number of different structures, with very different properties. Understanding such properties is essential to making quality titanium hydride. At room temperature, the most stable form of titanium is the hexagonal close-packed (HCP) structure α-titanium. It is a fairly hard metal that can dissolve only a small concentration of hydrogen, no more than 0.20 wt% at 464 °C (867 °F), and only 0.02% at 25 °C (77 °F). If titanium hydride contains more than 0.20% hydrogen at titanium hydride-making temperatures it transforms into a body-centred cubic (BCC) structure called β-titanium. It can dissolve considerably more hydrogen, more than 2.1% hydrogen at 636 °C (1,177 °F). If titanium hydride contains more than 2.1% at 636 °C (1,177 °F) then it transforms into a face-centred cubic (FCC) structure called δ-titanium. It can dissolve even more hydrogen, as much as 4.0% hydrogen 37 °C (99 °F), which reflects the upper hydrogen content of titanium hydride. [16]

There are many types of heat treating processes available to titanium hydride. The most common are annealing and quenching. Annealing is the process of heating the titanium hydride to a sufficiently high temperature to soften it. This process occurs through three phases: recovery, recrystallization, and grain growth. The temperature required to anneal titanium hydride depends on the type of annealing. Annealing must be done under a hydrogen atmosphere to prevent outgassing.

See also

Related Research Articles

Palladium hydride is palladium metal with hydrogen within its crystal lattice. Despite its name, it is not an ionic hydride but rather an alloy of palladium with metallic hydrogen that can be written PdHx. At room temperature, palladium hydrides may contain two crystalline phases, α and β. Pure α-phase exists at x < 0.017 while pure β-phase exists at x > 0.58; intermediate x values correspond to α-β mixtures.

Nickel hydride is either an inorganic compound of the formula NiHx or any of a variety of coordination complexes. It was discovered by Polish chemist Bogdan Baranowski in 1958.

<span class="mw-page-title-main">Lithium aluminium hydride</span> Chemical compound

Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li[AlH4] or LiAlH4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.

<span class="mw-page-title-main">Hydrogen embrittlement</span> Reduction in ductility of a metal exposed to hydrogen

Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.

<span class="mw-page-title-main">Titanium diboride</span> Chemical compound

Titanium diboride (TiB2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and wear resistance. TiB2 is also a reasonable electrical conductor, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining.

<span class="mw-page-title-main">Sodium borohydride</span> Chemical compound

Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. It is a white crystalline solid, usually encountered as an aqueous basic solution. Sodium borohydride is a reducing agent that finds application in papermaking and dye industries. It is also used as a reagent in organic synthesis.

<span class="mw-page-title-main">Titanium alloys</span> Metal alloys made by combining titanium with other elements

Titanium alloys are alloys that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness. They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures. However, the high cost of processing limits their use to military applications, aircraft, spacecraft, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.

<span class="mw-page-title-main">Zirconium alloys</span> Zircaloy family

Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. One of the main uses of zirconium alloys is in nuclear technology, as cladding of fuel rods in nuclear reactors, especially water reactors. A typical composition of nuclear-grade zirconium alloys is more than 95 weight percent zirconium and less than 2% of tin, niobium, iron, chromium, nickel and other metals, which are added to improve mechanical properties and corrosion resistance.

<span class="mw-page-title-main">Zirconium hydride</span> Alloy of zirconium and hydrogen

Zirconium hydride describes an alloy made by combining zirconium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the zirconium atom crystal lattice from sliding past one another. Varying the amount of hydrogen and the form of its presence in the zirconium hydride controls qualities such as the hardness, ductility, and tensile strength of the resulting zirconium hydride. Zirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.

<span class="mw-page-title-main">Calcium hydride</span> Chemical compound

Calcium hydride is the chemical compound with the formula CaH2, an alkaline earth hydride. This grey powder reacts vigorously with water liberating hydrogen gas. CaH2 is thus used as a drying agent, i.e. a desiccant.

Titanium powder metallurgy (P/M) offers the possibility of creating net shape or near net shape parts without the material loss and cost associated with having to machine intricate components from wrought billet. Powders can be produced by the blended elemental technique or by pre-alloying and then consolidated by metal injection moulding, hot isostatic pressing, direct powder rolling or laser engineered net shaping.

<span class="mw-page-title-main">Magnesium hydride</span> Chemical compound

Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.

<span class="mw-page-title-main">Allotropes of boron</span> Materials made only out of boron

Boron can be prepared in several crystalline and amorphous forms. Well known crystalline forms are α-rhombohedral (α-R), β-rhombohedral (β-R), and β-tetragonal (β-T). In special circumstances, boron can also be synthesized in the form of its α-tetragonal (α-T) and γ-orthorhombic (γ) allotropes. Two amorphous forms, one a finely divided powder and the other a glassy solid, are also known. Although at least 14 more allotropes have been reported, these other forms are based on tenuous evidence or have not been experimentally confirmed, or are thought to represent mixed allotropes, or boron frameworks stabilized by impurities. Whereas the β-rhombohedral phase is the most stable and the others are metastable, the transformation rate is negligible at room temperature, and thus all five phases can exist at ambient conditions. Amorphous powder boron and polycrystalline β-rhombohedral boron are the most common forms. The latter allotrope is a very hard grey material, about ten percent lighter than aluminium and with a melting point (2080 °C) several hundred degrees higher than that of steel.

Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium.

Titanium(IV) hydride is an inorganic compound with the empirical chemical formula TiH
4. It has not yet been obtained in bulk, hence its bulk properties remain unknown. However, molecular titanium(IV) hydride has been isolated in solid gas matrices. The molecular form is a colourless gas, and very unstable toward thermal decomposition. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.

Chromium hydrides are compounds of chromium and hydrogen, and possibly other elements. Intermetallic compounds with not-quite-stoichometric quantities of hydrogen exist, as well as highly reactive molecules. When present at low concentrations, hydrogen and certain other elements alloyed with chromium act as softening agents that enables the movement of dislocations that otherwise not occur in the crystal lattices of chromium atoms.

Scandium hydride, also known as scandium–hydrogen alloy, is an alloy made by combining scandium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the scandium atom crystal lattice from sliding past one another. Varying the amount of hydrogen controls qualities such as the hardness of the resulting scandium hydride. Scandium hydride with increased hydrogen content can be made harder than scandium.

<span class="mw-page-title-main">Titanium biocompatibility</span>

Titanium was first introduced into surgeries in the 1950s after having been used in dentistry for a decade prior. It is now the metal of choice for prosthetics, internal fixation, inner body devices, and instrumentation. Titanium is used from head to toe in biomedical implants. One can find titanium in neurosurgery, bone conduction hearing aids, false eye implants, spinal fusion cages, pacemakers, toe implants, and shoulder/elbow/hip/knee replacements along with many more. The main reason why titanium is often used in the body is due to titanium's biocompatibility and, with surface modifications, bioactive surface. The surface characteristics that affect biocompatibility are surface texture, steric hindrance, binding sites, and hydrophobicity (wetting). These characteristics are optimized to create an ideal cellular response. Some medical implants, as well as parts of surgical instruments are coated with titanium nitride (TiN).

Iron(II) hydride, systematically named iron dihydride and poly(dihydridoiron) is solid inorganic compound with the chemical formula (FeH
2)
n (also written ([FeH
2])n or FeH
2). ). It is kinetically unstable at ambient temperature, and as such, little is known about its bulk properties. However, it is known as a black, amorphous powder, which was synthesised for the first time in 2014.

<span class="mw-page-title-main">Iron–hydrogen alloy</span>

Iron–hydrogen alloy, also known as iron hydride, is an alloy of iron and hydrogen and other elements. Because of its lability when removed from a hydrogen atmosphere, it has no uses as a structural material.

References

  1. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  2. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN   0-12-352651-5.
  3. 1 2 3 4 5 Rittmeyer, Peter; Weitelmann, Ulrich (2005). "Hydrides". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a13_199. ISBN   978-3-527-30673-2.
  4. ↑ McQuillan, A. D. (22 December 1950). "An experimental and thermodynamic investigation of the hydrogen-titanium system". Proceedings of the Royal Society A. 204 (1078): 309–323. Bibcode:1950RSPSA.204..309M. doi:10.1098/rspa.1950.0176. S2CID   135759594 . Retrieved 10 March 2013.
  5. ↑ Bennett, L. H. (1980). "Nuclear magnetic resonance in alloys". MRS Proceedings. 3. doi:10.1557/PROC-3-3 . Retrieved 10 March 2013.
  6. ↑ Wang, Xin-Quan; Wang, Jian-Tao (15 June 2010). "Structural stability and hydrogen diffusion in TiHx alloys". Solid State Communications. 150 (35–36): 1715–1718. Bibcode:2010SSCom.150.1715W. doi:10.1016/j.ssc.2010.06.004 . Retrieved 10 March 2013.
  7. 1 2 M. Baudler "Hydrogen, Deuterium, Water" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 114-115.
  8. ↑ Millenbach, Pauline; Givon, Meir (1 October 1982). "The electrochemical formation of titanium hydride". Journal of the Less Common Metals. 87 (2): 179–184. doi:10.1016/0022-5088(82)90086-8 . Retrieved 10 March 2013.
  9. ↑ Zhang, Heng; Kisi, Erich H (1997). "Formation of titanium hydride at room temperature by ball milling". Journal of Physics: Condensed Matter. 9 (11): L185–L190. Bibcode:1997JPCM....9L.185Z. doi:10.1088/0953-8984/9/11/005. ISSN   0953-8984. S2CID   250853926.
  10. ↑ Paulin, Irena; Donik, Črtomir; Mandrino, Djordje; Vončina, Maja; Jenko, Monika (January 2012). "Surface characterization of titanium hydride powder". Vacuum. 86 (6): 608–613. doi:10.1016/j.vacuum.2011.07.054.
  11. ↑ Brown, Charles C.; Buxbaum, Robert E. (June 1988). "Kinetics of hydrogen absorption in alpha titanium". Metallurgical Transactions A. 19 (6): 1425–1427. Bibcode:1988MTA....19.1425B. doi:10.1007/bf02674016. S2CID   95614680.
  12. 1 2 Fukai, Y (2005). The Metal-Hydrogen System, Basic Bulk Properties, 2d edition. Springer. ISBN   978-3-540-00494-3.
  13. ↑ Numakura, H; Koiwa, M; Asano, H; Izumi, F (1988). "Neutron diffraction study of the metastable γ titanium deuteride". Acta Metallurgica. 36 (8): 2267–2273. doi:10.1016/0001-6160(88)90326-4. ISSN   0001-6160.
  14. 1 2 3 Donachie, Matthew J. (2000). Titanium: A Technical Guide. ASM International. ISBN   978-0-87170-686-7.
  15. ↑ Lu, Gang; Bernasek, Steven L.; Schwartz, Jeffrey (2000). "Oxidation of a polycrystalline titanium surface by oxygen and water". Surface Science. 458 (1–3): 80–90. Bibcode:2000SurSc.458...80L. doi:10.1016/S0039-6028(00)00420-9. ISSN   0039-6028.
  16. ↑ Setoyama, Daigo; Matsunaga, Junji; Muta, Hiroaki; Uno, Masayohi; Yamanaka, Shinsuke (3 November 2004). "Mechanical properties of titanium hydride". Journal of Alloys and Compounds. 381 (1–2): 215–220. doi:10.1016/j.jallcom.2004.04.073.
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