Triuranium octoxide

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Triuranium octoxide
Other names	pitchblende
Identifiers
CAS number	[1317-99-3]
Properties
Molecular formula	U3O8
Molar mass	842.1 g/mol
Melting point	1150°C
Boiling point	decomposes to UO2 at 1300 °C
Solubility in other solvents	Insoluble in water; Soluble in nitric and sulfuric acids.
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Triuranium octoxide (U₃O₈) is a compound of uranium. It presents as an olive green to black, odorless solid. In spite of its color, it is one of the more popular forms of yellowcake and is shipped between mills and refineries in this form.

Triuranium octoxide occurs naturally as the olive-green-colored mineral pitchblende. U₃O₈ is readily produced from UF₆ and has potential long-term stability in a geologic environment. In the presence of oxygen (O₂), uranium dioxide (UO₂) is oxidized to U₃O₈, whereas uranium trioxide (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 (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 and also because it is the form of uranium found in nature. Its particle density is 8.3 g cm⁻³.

[edit] Solid state structure

The solid is a layered structure where the layers are bridged by oxygen atoms, each layer contains uranium atoms which are in different coordination environments in the above diagram these are shown in plum and green.

[edit] Bond valence study

Using a 6Å x 6Å x 6Å 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 respectively for U1 and U2. These study suggests that all the uranium atoms have the same oxidation state, so that the oxidation states are disordered through the lattice.

[edit] References

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