Hafnium(IV) carbide

Hafnium(IV) carbide
Identifiers
CAS number 12069-85-1 Y
ChemSpider 17340381 Y
Jmol-3D images Image 1
Properties
Molecular formula HfC
Molar mass 190.50 g/mol
Appearance black odorless powder
Density 12.2 g/cm3[1]
Melting point

3900 °C[2]
Solubility in water insoluble
Structure
Crystal structure cubic, cF8
Space group Fm3m, No. 225
Hazards
EU classification not listed
NFPA 704
2
2
1
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hafnium carbide (HfC) is a chemical compound of hafnium and carbon. With a melting point of about 3900 °C it is one of the most refractory binary compounds known.[2] However, it has a low oxidation resistance, with the oxidation starting at temperatures as low as 430 °C.[3]

Hafnium carbide is usually carbon deficient and therefore its composition is often expressed as HfCx (x = 0.5 to 1.0). It has a cubic (rock-salt) crystal structure at any value of x.[4]

Hafnium carbide powder is obtained by the reduction of hafnium(IV) oxide with carbon at 1800 to 2000 °C. A long processing time is required to remove all oxygen. Alternatively, high-purity HfC coatings can be obtained by chemical vapor deposition from a gas mixture of methane, hydrogen, and vaporized hafnium(IV) chloride. Because of the technical complexity and high cost of the synthesis, HfC has a very limited use, despite its favorable properties such as high hardness and melting point.[2]

The magnetic properties of HfCx change from paramagnetic for x ≤ 0.8 to diamagnetic at larger x. An inverse behavior (dia-paramagnetic transition with increasing x) is observed for TaCx, despite its having the same crystal structure as HfCx.[5]

References

  1. ^ Physical Constants of Inorganic Compounds in Lide, D. R., ed (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. pp. 4–44 ff.. ISBN 0-8493-0486-5. 
  2. ^ a b c Harry Julius Emeléus (1968). Advances in Inorganic Chemistry and Radiochemistry. Academic Press. pp. 169–170. ISBN 9780120236114. http://books.google.com/books?id=-SnCsg5jM_kC&pg=PA169. Retrieved 3 May 2011. 
  3. ^ . doi:10.1111/j.1151-2916.1992.tb05487.x. 
  4. ^ Lavrentyev, A; Gabrelian, B; Vorzhev, V; Nikiforov, I; Khyzhun, O; Rehr, J (2008). "Electronic structure of cubic HfxTa1–xCy carbides from X-ray spectroscopy studies and cluster self-consistent calculations". Journal of Alloys and Compounds 462: 4–10. doi:10.1016/j.jallcom.2007.08.018. 
  5. ^ Aleksandr Ivanovich Gusev; Andreĭ Andreevich Rempel; Andreas J. Magerl (2001). Disorder and order in strongly nonstoichiometric compounds: transition metal carbides, nitrides, and oxides. Springer. pp. 513–516. ISBN 9783540418177. http://books.google.com/books?id=jc2D7TGZcyUC&pg=PA513. Retrieved 3 May 2011.