Binary Fluorides of Uranium

There are several binary fluorides of uranium in which the formal valence state of uranium ranges from 3 to 6 like UF3, UF4, UF5, UFg, U2F9, U4F17, and U4F18. The two most important of these with regard to the NFC are UF4 and UFg and will be briefly discussed here. The other binary fluorides will be mentioned in context in the appropriate sections of this book. 

If oxygen is also present, then uranyl fluoride (UOjFj) may be formed. Heating UF4 in dry air above 300°C may lead to formation of uranyl fluoride and UjOg (Galkin 1966). An interesting reaction of UF4 with pure dry oxygen at 800°C may lead to formation of UF without the need to use fluorine (Equation 1.2)  

The reaction of UF4 with fluorine at 250 C-400 C results in the formation of UFg, but it should be noted that nonvolatile intermediate uranium-fluorides (UF44,j, x = 0-2) like those listed earlier may also be formed. Stroug fluorinating ageuts, for example, CIF3 or Brp3, may react with UF4 at lower tanperatures to form UFg. 

Uranium tetrafluoride forms stable coordination complex fluorides with ammonium fluoride and many alkali and alkaU-earth fluorides like NH4UF5 or Na2UFg and several other fluoride compounds. The melting point of the complex double salts formed in the NaF-Up4 system is much lower than that of the components (Galkin 1966). 

UFg is produced commercially by the reaction of UF4 with fluorine (Equation 1.3), but in practice it can be produced by the action of any strong fluorinating agent (like CIF3, BrFj, etc.) on any uranium compound (metal, oxide, U-containing mineral, etc.) under proper conditions  

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