Uranium tetrafluoride is the inorganic compound with the formulaUF4. It is a green solid with an insignificant vapor pressure and low solubilityinwater. Uranium in its tetravalent (uranous) state is important in various technological processes. In the uranium refining industry it is known as green salt.[1]
UF4 is prepared from UO2 in a fluidized bed by reaction with HF. The UO2 is derived from mining operations. Around 60,000 tonnes per year are prepared in this way annually. A common impurity is UO2F2. UF4 is susceptible to hydrolysis as well.[1]
UF4 is formed by the reaction of UF6 with hydrogen gas in a vertical tube-type reactor.
UF4 is less stable than the uranium oxides and reacts slowly with moisture at ambient temperature, forming UO2 and HF, the latter of which is very corrosive and toxic; it is thus less favourable for long-term disposal. 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.
Amolten 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 other salts because of the usefulness of the elements without isotope separation, better neutron economy and moderating efficiency, lower vapor pressure and better chemical stability.
Like most 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.[2][3]
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.
"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.
