Uranium tetrafluoride is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

UF₄. It is a green solid with an insignificant

vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed pha ...

and low

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

. 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 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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

as well. 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 Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a sub ...

; it is thus less favourable for long-term disposal. The bulk

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

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 A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

where the working fluid is a

molten salt Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.Journal of Chemical T ...

, would use UF₄ as the core material. UF₄ is generally chosen over other salts because of the usefulness of the elements without

isotope separation Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research (e.g. in chemistry where atoms of "marker" ...

, better neutron economy and moderating efficiency, lower

and better chemical stability.

Reactions

Uranium tetrafluoride reacts with fluorine, first to give uranium pentafluoride and then volatile UF₆: :2UF₄ + F₂ → 2UF₅ :2UF₅ + F₂ → 2UF₆ UF₄ is reduced by

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

to give the metal: :UF₄ + 2Mg → U + 2MgF₂ 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 X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

, the U centres are eight-coordinate with square antiprismatic coordination spheres. The fluoride centres are doubly bridging.

Safety

Like all uranium salts, UF₄ is

and thus harmful by inhalation, ingestion, and through skin contact. : Uranium tetrafluoride

References of historical interest

References

External links

* {{DEFAULTSORT:Uranium Tetrafluoride Uranium(IV) compounds Nuclear materials Fluorides Actinide halides Inorganic compounds