Uranium (V, VI) oxide

Crystal structure
__ U 5 + / 6 +      __ O 2−
General
Surname	Uranium (V, VI) oxide
other names	Triurane octoxide
Ratio formula	U 3 O 8
Brief description	greenish black orthorhombic crystals
External identifiers / databases
CAS number 1344-59-8 EC number 215-702-4 ECHA InfoCard 100.014.275 PubChem 11968241 Wikidata Q65920890
properties
Molar mass	842.08 g mol −1
Physical state	firmly
density	8.38 g cm −3
Melting point	1300 ° C (decomp.)
solubility	almost insoluble in water
Hazard and safety information
Radioactive
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 330-300-373-411 P: ?
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Uranium (V, VI) oxide (also triurane octoxide , U ₃ O ₈ ) is a chemical compound of uranium and is one of the oxides . It comes in several modifications . Pitchblende does not contain uranium (V, VI) oxide, but uranium (IV) oxide and additional oxygen .

presentation

Uranium (V, VI) oxide is formed when uranium (VI) oxide is heated to 700–900 ° C by releasing oxygen or from uranium (IV) oxide by absorbing oxygen. It is also formed when other uranium oxides are heated to similar temperatures in the air.

${\displaystyle \mathrm {3\ UO_{2}+O_{2}\longrightarrow U_{3}O_{8}} }$

properties

Physical Properties

Uranium (V, VI) oxide forms several modifications. In pure uranium (V, VI) oxide, the orthorhombic α-structure with the space group  C 2 mm (No. 38, position 4) and the lattice parameters a = 671 pm, b = 1196 pm and c = 414 pm is thermodynamic at room temperature stable. Above 210 ° C it reversibly changes into a hexagonal shape (a = 681 pm, c = 414 pm, space group  P 6 2 m (No. 189) ). The orthorhombic β-structure with the space group Cmcm (No. 63) and the lattice parameters a = 707 pm, b = 1145 pm and c = 830 pm, obtained by heating α-U ₃ O ₈ to 1350 ° C, is  metastable at room temperature can be formed in the open air and slowly cooling. In addition, a cubic, substoichiometric modification which is only stable at high pressure is known.

Uranium (V, VI) oxide is conductive depending on the oxygen content; at room temperature the electrical conductivity for exactly stoichiometric uranium (V, VI) oxide is about 100  Ω ⁻¹ · m ⁻¹ . The compound is an n-type semiconductor .

Freshly produced uranium (V, VI) oxide from earthly natural uranium has a specific activity of 21450 Bq / g.

Chemical properties

Triurane octoxide dissolves easily in oxidizing acids with the formation of uranyl ions . The reaction with hydrogen chloride at 700 ° C produces uranyl chloride .

By reacting with hydrogen at 700 ° C or carbon monoxide at 350 ° C, it is reduced to uranium (IV) oxide via several non-stoichiometric intermediate products.

use

Since uranium (V, VI) oxide is produced from all uranium oxides at the same temperature, it is used for gravimetric determination of the uranium content, for example of ores.

literature

• Ingmar Grenthe, Janusz Drożdżynński, Takeo Fujino, Edgar C. Buck, Thomas E. Albrecht-Schmitt, Stephen F. Wolf: Uranium , in: Lester R. Morss, Norman M. Edelstein, Jean Fuger (eds.): The Chemistry of the Actinide and Transactinide Elements. Springer, Dordrecht 2006, ISBN 1-4020-3555-1 , pp. 253-698 ( doi : 10.1007 / 1-4020-3598-5_5 ).

Individual evidence

1. ↑ ^{a b c} David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Properties of the Elements and Inorganic Compounds, pp. 4-97.
2. ↑ ^{a b c d} Martin Peehs, Thomas Walter, Sabine Walter, Martin Zemek: Uranium, Uranium Alloys, and Uranium Compounds. In: Ullmann's Encyclopedia of Industrial Chemistry , Wiley-VCH, 2007 ( doi : 10.1002 / 14356007.a27_281.pub2 ).
3. ↑ Entry on uranium compounds in the GESTIS substance database of the IFA , accessed on February 1, 2016 (JavaScript required)
4. ↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry uranium compounds with the exception of those specified elsewhere in this Annex in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA) , accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
5. ↑ The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling.
6. ↑ Entry on Uranpecherz. In: Römpp Online . Georg Thieme Verlag, accessed on August 27, 2012.
7. ↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 1227.
8. ^ ^{A b c} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1971.
9. ↑ BO Loopstra: The Phase Transition in α-U ₃ O ₈ at 210 ° C. In: Journal of Applied Crystallography , 1970 , 3 , pp. 94-96 ( doi : 10.1107 / S002188987000571X ).
10. ↑ BO Loopstra: The structure of β-U ₃ O ₈ . In: Acta Crystallographica B , 1970 , 26 , pp. 656-657 ( doi : 10.1107 / S0567740870002935 ).