• Source: Uranium tetrafluoride

Uranium tetrafluoride is the inorganic compound with the formula UF4. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent (uranous) state is important in various technological processes. In the uranium refining industry it is known as green salt.




Production


UF4 is prepared from UO2 in a fluidized bed by reaction with Hydrogen fluoride. The UO2 is derived from mining operations. Around 60,000 tonnes are prepared in this way annually. A common impurity is UO2F2. UF4 is susceptible to hydrolysis as well.
UF4 is formed by the reaction of UF6 with hydrogen gas in a vertical tube-type reactor.
The bulk density of UF4 varies from about 2.0 g/cm3 to about 4.5 g/cm3 depending on the production process and the properties of the starting uranium compounds.
A molten salt reactor design, a type of nuclear reactor where the working fluid is a molten salt, would use UF4 as the core material. UF4 is generally chosen over related compounds because of the usefulness of the elements without isotope separation, better neutron economy and moderating efficiency, lower vapor pressure and better chemical stability.




Reactions


Uranium tetrafluoride reacts stepwise with fluorine, first to give uranium pentafluoride and then volatile UF6:

2 UF4 + F2 → 2 UF5
2 UF5 + F2 → 2 UF6
UF4 is reduced by magnesium to give the metal:

UF4 + 2 Mg → U + 2 MgF2
UF4 reacts slowly with moisture at ambient temperature, forming UO2 and HF.




Structure


Like most binary metal fluorides, UF4 is a dense highly crosslinked inorganic polymer. As established by X-ray crystallography, the U centres are eight-coordinate with square antiprismatic coordination spheres. The fluoride centres are doubly bridging.




Safety


Like all uranium salts, UF4 is toxic and thus harmful by inhalation, ingestion, and through skin contact.




See also


Praseodymium(IV) fluoride which has the same crystal structure




References of historical interest


Booth, H. S.; Krasny-Ergen, W.; Heath, R. E. (1946). "Uranium Tetrafluoride". Journal of the American Chemical Society. 68 (10): 1969. doi:10.1021/ja01214a028.




References






External links


"Uranium Tetrafluoride". Appendix A of the PEIS (DOE/EIS-0269). Argonne National Laboratory. Archived from the original on 30 January 2016. Retrieved 22 November 2011.

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