Chromium(III) oxide
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| Chromium(III) oxide | |
|---|---|
| Other names | Chromium sesquioxide Chromia Chrome green |
| Molecular formula | Cr2O3 |
| Molar mass | 151.99 g/mol |
| CAS number | [12018-34-7] |
| Density | 5.21 g/cm3 |
| Solubility (water) | Insoluble |
| color | dull green |
| Melting point | 2435 °C (4415 °F) |
| Boiling point | approx. 4000 °C (7250 °F) |
| Disclaimer and references | |
Chromium(III) oxide, also known as chromium sesquioxide or chromia, is one of four oxides of chromium, chemical formula Cr2O3. It is commonly called chrome green when used as a pigment; however it was referred to as viridian when it was first discovered. The Parisians Pannetier and Binet first prepared Cr2O3 in 1838 via a secret process. It is manufactured from the mineral chromite, Fe(CrO2)2, which is mined in southern Africa, Asia, Turkey and Cuba. The conversion of chromite to chromia entails air oxidation to Na2Cr2O7, which is subsequently reduced with carbon or sulfur.
Cr2O3 is an amphoteric oxide, dissolving in acids to give chromium(III) salts and in molten alkali to give chromites. It is also a good absorbent in process of adsorption.
Chromium oxide can be made into elemental chromium metal through the thermite reaction, though this metal oxide is much less commonly used than Fe2O3 and Fe3O4. 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.
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[edit] Precautions
Though Cr2O3 is not a serious health hazard, it can cause irritation of the skin and eyes, and can cause nausea and other problems if ingested. It also can cause respiratory problems when dust is inhaled. It is not a fire hazard, and does not readily react with other materials.
[edit] References
- A. F. Hollemann and E. Wiberg "Inorganic Chemistry" Academic Press, 2001, New York.
