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.
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 (>9 Mohs) and melting point.
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.
^Shimada, Shiro (1992). "Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480o to 600oC". Journal of the American Ceramic Society75 (10): 2671–2678. doi:10.1111/j.1151-2916.1992.tb05487.x.
^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 Compounds462 (1-2): 4–10. doi:10.1016/j.jallcom.2007.08.018.
^CRC Materials Science and Engineering Handbook (2001).