Cobalt (II, III) oxide
Crystal structure | |||||||||||||||||||
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__ Co 3+ __ Co 2+ __ O 2− | |||||||||||||||||||
General | |||||||||||||||||||
Surname | Cobalt (II, III) oxide | ||||||||||||||||||
other names |
Tricobalt tetraoxide |
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Ratio formula | Co 3 O 4 | ||||||||||||||||||
Brief description |
black odorless solid |
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External identifiers / databases | |||||||||||||||||||
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properties | |||||||||||||||||||
Molar mass | 240.8 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
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density |
6.11 g cm −3 (20 ° C) |
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Melting point |
> 900 ° C (decomposition) |
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solubility |
almost insoluble in water |
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safety instructions | |||||||||||||||||||
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Toxicological data | |||||||||||||||||||
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . |
Cobalt (II, III) oxide is a chemical compound of cobalt and oxygen . The black solid is one of several oxides of cobalt and belongs to the group of spinels .
Extraction and presentation
Cobalt (II, III) oxide is formed when cobalt (II) oxide is heated in air to 400 to 500 ° C.
properties
Cobalt (II, III) oxide is a mixed-valent compound with divalent and trivalent cobalt ions and the more precise formula Co 2+ Co 3+ 2 O 4 (CoO · Co 2 O 3 ). The compound has a spinel structure in which one eighth of all tetrahedral gaps and half of the octahedral gaps are occupied by cobalt ions in a cubic closest packing of spheres by O 2− ions . The Co 2+ ions occupy the tetrahedral gaps, the Co 3+ ions the octahedral gaps. The crystals have the space group Fd 3 m (space group no. 227) , the lattice parameter a = 809 pm. In the unit cell there are eight formula units .
From around 900 ° C cobalt (II, III) oxide decomposes to cobalt (II) oxide. The compound is reduced to elemental cobalt by reducing agents such as coke or aluminum .
Cobalt (II, III) oxide is insoluble in hydrochloric acid , nitric acid and aqua regia , but soluble in concentrated sulfuric acid and in molten potassium hydrogen sulfate .
use
Cobalt (II, III) oxide is an important intermediate product in the production of metallic cobalt. By roasting and leaching , cobalt (II, III) oxide is first obtained from various cobalt ores (mostly sulfides or arsenides ). This can now be reduced to the element with carbon or aluminothermically .
Cobalt (II, III) oxide can be used as a catalyst for the oxidation of ammonia to nitric acid. This is significantly cheaper than the platinum alloys otherwise used . One disadvantage, however, is the hitherto lower selectivity of cobalt (II, III) oxide catalysts.
Like other cobalt compounds, cobalt (II, III) oxide is a blue pigment for coloring ceramics.
safety instructions
Cobalt (II, III) oxide is considered to be carcinogenic and germ cell mutagenic .
Individual evidence
- ↑ a b c d e f g h i Entry on cobalt (II, III) oxide in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
- ^ A b c d A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 1682-1687.
- ^ A b Jean D'Ans, Ellen Lax: Paperback for chemists and physicists. 3. Elements, inorganic compounds and materials, minerals, Volume 3. 4. Edition, Springer, 1997, ISBN 978-3-540-60035-0 , p. 388 ( limited preview in Google book search).
- ↑ Poul Erik Højlund Nielsen, Keld Johansen: Ammonia oxidation Catalyst . EP19930104797 , 1993.
- ^ Fa. Lehrer: Raw material overview ceramics ( Memento of January 8, 2004 in the Internet Archive )