Titanium hydride
 Titanium hydride powder
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| Names | |
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IUPAC name
titanium dihydride (hydrogen deficient)
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| Identifiers | |
7704-98-5 
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| ECHA InfoCard | 100.028.843 |
| PubChem | 197094 |
| Properties | |
| TiH2-x | |
| Molar mass | 49.88 g/mol (TiH2) |
| Appearance | black powder (commercial form) |
| Density | 3.76 g/cm3 (typical commercial form) |
| Melting point | 350 °C (662 °F; 623 K) approximately |
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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. 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.
In the commercial process for producing non-stoichiometric TiH(2-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. In the laboratory, titanium hydride is produced by heating titanium powder under flowing hydrogen at 700 °C, the idealized equation being:
Other methods of producing titanium hydride include electrochemical and ball milling methods.
TiH1.95 is unaffected by water and air. It is slowly attacked by strong acids and is degraded by hydrofluoric and hot sulfuric acids. It reacts rapidly with oxidising agents, this reactivity leading to the use of titanium hydride in pyrotechnics.
The material has been used to produce highly pure hydrogen, which is released upon heating the solid starting at 300 °C. Only at the melting point of titanium is dissociation complete. Titanium tritiide has been proposed for the long-term storage of tritium gas.
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. 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 an 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.
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