Uranium hexafluoride
uranium enrichment process that produces fuel for nuclear reactors and bombs. It forms solid grey crystals at standard temperature and pressure (STP), is highly toxic, reacts violently with water and is corrosive to most metals. It reacts mildly with aluminum, forming a thin surface layer of Al2F3 that resists further reaction.
Milled uranium ore -- U3O8, or "yellowcake" -- is dissolved in nitric acid, yielding a solution of uranyl nitrate UO2(NO3)2. Pure uranyl nitrate is obtained by solvent extraction, then treated with ammonia to produce ammonium diuranate (ADU). Reduction with hydrogen gives UO2, which is converted with hydrofluoric acid (HF) to UF4. Oxidation with fluorine finally yields UF6.
It is used in the uranium enrichment process because it has a triple point at 147 °C and slightly higher than normal atmospheric pressure. This makes it very economical to process using the gaseous diffusion method. Isotopes of UF6 differ in their molecular weight based solely on the uranium isotope present, as fluorine has only a single stable naturally occurring isotope. By subjecting UF6 to repeated boiling and condensing, separation of U-235 from U-238 occurs by statistical enrichment. This process is very energy intensive.
