Uranium nitride
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IUPAC name
Uranium nitride
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| Identifiers | |
| Properties | |
| U2N3 | |
| Molar mass | 518.078 g/mol |
| Appearance | crystalline solid |
| Density | 11300 kg·m−3, solid |
| Melting point | 900 to 1,100 °C (1,650 to 2,010 °F; 1,170 to 1,370 K) (decomposes to UN) |
| Boiling point | Decomposes |
| 0.08 g/100 ml (20 °C) | |
| Structure | |
| Hexagonal, hP5 | |
| P-3m1, No. 164 | |
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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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Uranium nitride refers to a family of several ceramic materials: uranium mononitride (UN), uranium sesquinitride (U2N3) and uranium dinitride (UN2). The word nitride refers to the −3 oxidation state of the nitrogen bound to the uranium.
Uranium nitride has been considered as a potential fuel for nuclear reactors. It is said to be safer, stronger, denser, more thermally conductive and having a higher temperature tolerance. Challenges to implementation of the fuel include a complex conversion route from enriched UF6, the need to prevent oxidation during manufacturing and the need to define and license a final disposal route.
The common techniques for generating UN is carbothermic reduction of uranium oxide (UO2) in a 2 step method illustrated below.
Sol-gel methods and arc melting of pure uranium under nitrogen atmosphere can also be used.
Another common technique for generating UN2 is the ammonolysis of uranium tetrafluoride. Uranium tetrafluoride is exposed to ammonia gas under high pressure and temperature, which replaces the fluorine with nitrogen and generates hydrogen fluoride. Hydrogen fluoride is a colourless gas at this temperature and mixes with the ammonia gas.
An additional method of UN synthesis employs fabrication directly from metallic uranium. By exposing metallic uranium to hydrogen gas at temperatures in excess of 280 °C, UH3 can be formed. Furthermore, since UH3 has a lower specific volume than the metallic phase, hydridation can be used to physically decompose otherwise solid uranium. Following hydridation, UH3 can be exposed to a nitrogen atmosphere at temperatures around 500 °C, thereby forming U2N3. By additional heating to temperatures above 1150 °C, the sesquinitride can then be decomposed to UN.
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