Triuranium octoxide (U₃O₈) is a compound of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

. It is present as an olive green to black, odorless solid. It is one of the more popular forms of

yellowcake Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before f ...

and is shipped between mills and refineries in this form. U₃O₈ has potential long-term stability in a geologic environment. In the presence of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

(O₂),

uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear re ...

(UO₂) is

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

to U₃O₈, whereas

uranium trioxide Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is a ...

(UO₃) loses oxygen at temperatures above 500 °C and is reduced to U₃O₈. The compound can be produced by any one of three primary chemical conversion processes, involving either

uranium tetrafluoride 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 process ...

(UF₄) or uranyl fluoride (UO₂F₂) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U₃O₈ is one of the most kinetically and thermodynamically stable forms of uranium. Its particle density is 8.3 g cm⁻³. Triuranium octoxide is converted to uranium hexafluoride for the purpose of

uranium enrichment Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 ...

Solid state structure

The solid is a layered structure where the layers are bridged by

atoms, each layer contains uranium atoms which are in different coordination environments.

Bond valence study

Using a box with the uranium atom in the centre, the bond valence calculation was performed for both U1 and U2 in solid. It was found, using the parameters for U(VI), that the calculated oxidation states for U1 and U2 are 5.11 and 5.10. Using the parameters for U(IV), the calculated oxidation states are 5.78 and 5.77 for U1 and U2, respectively. These studies suggests that all the uranium atoms have the same oxidation state, so that the oxidation states are disordered through the lattice.

References

{{DEFAULTSORT:Uranium oxide Uranium(IV,VI) compounds Oxides Mixed valence compounds Nuclear materials