Uranium hydride
| Names | |
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| Other names
Uranium(III) hydride
Uranium trihydride Hypouranous hydride |
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| Identifiers | |
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3D model (Jmol)
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| ChemSpider | |
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| Properties | |
| UH 3 |
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| Molar mass | 241.05273 g mol−1 |
| Density | 10.95 g cm−3 |
| Reacts | |
| Structure | |
| Cubic, cP32 | |
| Pm3n, No. 223 | |
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a = 664.3 pm
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| Hazards | |
| Safety data sheet | ibilabs.com |
| Flash point | Pyrophoric |
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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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| Infobox references | |
Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium.
Uranium hydride is a highly toxic, brownish grey to brownish black pyrophoric powder or brittle solid. Its density at 20 °C is 10.95, much lower than that of uranium (19.1). It has a metallic conductivity, is slightly soluble in hydrochloric acid and decomposes in nitric acid.
Two crystal modifications of uranium hydride exist, both cubic: an α form that is obtained at low temperatures and a β form that is grown when the formation temperature is above 250 °C. After growth, both forms are metastable at room temperature and below, but the α form slowly converts to the β form upon heating to 100 °C. Both α- and β-UH3 are ferromagnetic at temperatures below ~180 K. Above 180 K, they are paramagnetic.
Exposition of uranium metal to hydrogen leads to hydrogen embrittlement. Hydrogen diffuses through metal and forms a network of brittle hydride over the grain boundaries. Hydrogen can be removed and ductility renewed by annealing in vacuum.
Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Further heating to about 500 °C will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds. The reversible reaction proceeds as follows:
Uranium hydride is not an interstitial compound, causing the metal to expand upon hydride formation. In its lattice, each uranium atom is surrounded by 6 other uranium atoms and 12 atoms of hydrogen; each hydrogen atom occupies a large tetrahedral hole in the lattice. The density of hydrogen in uranium hydride is approximately the same as in liquid water or in liquid hydrogen. The U-H-U linkage through a hydrogen atom is present in the structure.
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