Chromium(III) oxide
2492567
222661252
2008-06-30T14:13:16Z
24.17.60.11
Grammar
{{Chembox new
| Name = Chromium(III) oxide
| ImageFile = Chromium(III)-oxide-sample.jpg
<!-- | ImageSize = 250px -->
| ImageName = A sample of chromium(III) oxide
| OtherNames = Chromium sesquioxide<br />Chromia<br />Chrome green
| Section1 = {{Chembox Identifiers
| CASNo = 1308-38-9
}}
| Section2 = {{Chembox Properties
| Formula = Cr<sub>2</sub>O<sub>3</sub>
| MolarMass = 151.99 g/mol<br />
| MolarMass_notes = ''Cr=68.43%, O=31.57%''
| Solvent = other solvents
| SolubleOther = Insoluble
| MeltingPt = 2435 °C (4415 °F)
| BoilingPt = ''approx.'' 4000 °C (7250 °F)}}
}}
'''Chromium(III) oxide''' is the [[inorganic compound]] of the [[Chemical formula|formula]] Cr<sub>2</sub>O<sub>3</sub>. It is one of principal oxides of [[chromium]]. it is a widely used precursor to other chromium compounds.
==Structure and properties==
Cr<sub>2</sub>O<sub>3</sub> adopts the [[corundum]] structure, consisting of cubic close packed oxides with 2/3 of the octahedral holes occupied by chromium. It is [[antiferromagnetism|antiferromagnetic]] up to 307 K, the Neel temperature.<ref>J.E Greedon, (1994), ''Magnetic oxides'' in Encyclopedia of Inorganic chemistry Ed. R. Bruce King, John Wiley & Sons ISBN 0471936200</ref> It is an [[amphoteric oxide]], dissolving in acids to give chromium(III) [[salt]]s and in molten alkali to give [[Chromite (ion)|chromite]]s.
==Production==
The Parisians Pannetier and Binet first prepared Cr<sub>2</sub>O<sub>3</sub> in 1838 via a secret process. It is manufactured from the mineral [[chromite]], Fe(CrO<sub>2</sub>)<sub>2</sub>, which is mined in southern Africa, Asia, Turkey, and Cuba. The conversion of chromite to chromia entails air oxidation to Na<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>, which is subsequently reduced with carbon or sulfur.
Chromium oxide can be converted into elemental chromium metal through the [[thermite]] reaction, although this metal oxide is much less commonly used than Fe<sub>2</sub>O<sub>3</sub> and Fe<sub>3</sub>O<sub>4</sub>. Unlike iron oxide thermites, chromium oxide thermite creates little or no sparks, smoke or sound, but it glows with a blinding light. Because of the very high melting point of chromium, chromium thermite casting is impractical.
==Pigment==
It is commonly called chrome green or institutional green when used as a pigment; however it was referred to as [[viridian]] when it was first discovered.
==References==
{{Citationstyle|date=September 2007}}
<references/>
* A. F. Holleman and E. Wiberg "Inorganic Chemistry" Academic Press, 2001, New York.
==See also==
* [[Chromium(II) oxide]]
* [[Chromium(IV) oxide]]
* [[Chromic acid]]
==External links==
* [http://www.npi.gov.au/database/substance-info/profiles/24.html National Pollutant Inventory: Chromium (III) compounds fact sheet]
[[Category:Chromium compounds]]
[[Category:Oxides]]
[[Category:Inorganic pigments]]
[[Category:Alchemical substances]]
[[ar:أكسيد كروم ثلاثي]]
[[cs:Oxid chromitý]]
[[de:Chrom(III)-oxid]]
[[ja:オキサイド・オブ・クロミウム]]
[[pt:Óxido de cromo (III)]]
[[ru:Оксид хрома(III)]]
[[zh:三氧化二铬]]