Chromium carbide
| Chromium carbide[1] | |
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Chromium(II) carbide |
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| Identifiers | |
| CAS number | 12012-35-0  |
| PubChem | 3650773 |
| ChemSpider | 21171152 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | Cr3C2 |
| Molar mass | 180.009 g/mol |
| Appearance | gray orthorhombic crystals |
| Density | 6.68 g/cm3 |
| Melting point |
1895°C |
| Structure | |
| Crystal structure | Orthorhombic, oP20 |
| Space group | Pnma, No. 62 |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Chromium carbide (Cr3C2) is an extremely hard refractory ceramic material. It is usually processed by sintering. It has the appearance of a gray powder with orthorhombic crystal structure. The orthorhombic Cr3C2 occurs extremely rarely as mineral tongbaite.
Other compositions are available, e.g. Cr23C6 (occurring as extremely rare mineral isovite, cubic) and Cr7C3.
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[edit] Properties
It is highly corrosion-resistant, and does not oxidize at high temperatures (1000-1100 °C). The powder for coating costs $40–$65 per pound.
The thermal expansion coefficient of chromium carbide is almost equal to that of steel, reducing the mechanical stress buildup at the layer boundary.
Precipitation of chromium carbide at the grain boundaries, depleting the grain edges of chromium, is the cause of intergranular corrosion of stainless steel near the welds.
[edit] Uses
Chromium carbide is used as a thermal spray material for protecting the underlying metal surface, and as an additive to corrosion-resistant and wear-resistant materials. It is used in coatings of bearings, seals, orifices, and valve seals, and as a fine-crystal phase in other sintered carbides, where, like the vanadium carbide, it inhibits growth of submicrometre grains during pressing and sintering.
It is also used as a material for gage block standards, used in metrology. Chromium carbide is widely used by Starrett-Webber gage block tolerances, with a thermal expansion coefficient of 4.7 x 10^-6 inches/foot per inch.
[edit] References
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This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2009) |
- ^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–52, ISBN 0-8493-0594-2
[edit] External links
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