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 ...
UF
4. 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 ...
in
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 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 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 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 ...
and thus harmful by inhalation, ingestion, and through skin contact.
:
See also
*Praseodymium(IV) fluoride
Praseodymium(IV) fluoride (also praseodymium tetrafluoride) is a binary inorganic compound, a highly oxidised metal salt of praseodymium and fluoride with the chemical formula PrF4. It forms light yellow crystals.
Synthesis
Praseodymium(IV) fluor ...
which has the same crystal structure
References of historical interest
*
References
External links
*
{{DEFAULTSORT:Uranium Tetrafluoride
Uranium(IV) compounds
Nuclear materials
Fluorides
Actinide halides
Inorganic compounds