Uranium tetrafluoride is the

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

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 equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

and low

solubility In chemistry, solubility is the ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. Uranium in its tetravalent (

uranous Uranous is the chemical term for the reduced tetrapositive cation of uranium that exhibits the valence U4+. It is one of the two common ionic states of uranium found in nature, the other being the oxidised hexapositive ion called uranyl. 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 Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...

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

as well. UF₄ is formed by the reaction of UF₆ with hydrogen gas in a vertical tube-type reactor. The bulk

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

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 A molten-salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a mixture of molten salt with a fissile material. Two research MSRs operated in the United States in the mid-20th ...

design, a type of

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

where the working fluid is a

molten salt Molten salt is salt which is solid at standard temperature and pressure but liquified due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts ...

, would use UF₄ as the core material. UF₄ is generally chosen over related compounds 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" n ...

, better neutron economy and moderating efficiency, lower

and better chemical stability.

Reactions

Uranium tetrafluoride reacts stepwise with fluorine, first to give

uranium pentafluoride Uranium pentafluoride is the inorganic compound with the chemical formula UF5. It is a pale yellow paramagnetic solid. The compound has attracted interest because it is related to uranium hexafluoride, which is widely used to produce uranium fuel ...

and then volatile UF₆: :2UF₄ + F₂ → 2UF₅ :2UF₅ + F₂ → 2UF₆ UF₄ is reduced by

magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

to give the metal: :UF₄ + 2Mg → U + 2MgF₂ 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 In polymer chemistry, an inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the Polymer backbone, backbone. Polymers containing Inorganic compound, inorganic and Organic compound, organic components are ...

. As established by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

, 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 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 subst ...

and thus harmful by inhalation, ingestion, and through skin contact.

References of historical interest

References

External links

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