Uranium tetrafluoride

Uranium tetrafluoride

Names
IUPAC names Uranium(IV) fluoride Uranium tetrafluoride
Identifiers
CAS Number	10049-14-6 Y
3D model (JSmol)	Interactive image
ChemSpider	14676181 Y
ECHA InfoCard	100.030.142
EC Number	233-170-1
PubChem CID	61461
UNII	PJ46VTD8B2 Y
CompTox Dashboard (EPA)	DTXSID30892258
InChI InChI=1S/4FH.2U/h4*1H;;/q;;;;2*+2/p-4 Y Key: CWWZGQYYTNZESQ-UHFFFAOYSA-J Y InChI=1/4FH.2U/h4*1H;;/q;;;;2*+2/p-4 Key: CWWZGQYYTNZESQ-XBHQNQODAW
SMILES F[U](F)(F)F
Properties
Chemical formula	UF4
Molar mass	314.02 g/mol
Appearance	Green crystalline solid
Density	6.70 g/cm3, solid
Melting point	1,036 °C (1,897 °F; 1,309 K)
Boiling point	1,417 °C (2,583 °F; 1,690 K)
Solubility in water	Insoluble
Structure
Crystal structure	Monoclinic, mS60
Space group	C2/c, No. 15
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H300, H330, H373, H411
Flash point	Non-flammable
Safety data sheet (SDS)	External MSDS
Related compounds
Other anions	Uranium(IV) chloride Uranium(IV) bromide Uranium(IV) iodide Uranium dioxide
Other cations	Praseodymium(IV) fluoride Thorium(IV) fluoride Protactinium(IV) fluoride Neptunium(IV) fluoride Plutonium(IV) fluoride
Related compounds	Uranium hexafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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.^[1]

Production

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.

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 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.

Reactions

Uranium tetrafluoride reacts 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:^[2]

UF₄ + 2 Mg → U + 2 MgF₂

It is oxidized to UF₅ at room temperature and then, at 100 °C, to the hexafluoride.

Structure

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]

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.