Hafnium(IV) carbide

Hafnium carbide

Identifiers

CAS Number

* 12069-85-1 Y

3D model (JSmol)

* Interactive image

ChemSpider |

* 17340381 Y

PubChem CID

* 16212551

InChI

* InChI=1S/C.Hf/q-1;+1 Y

Key: NVDNLVYQHRUYJA-UHFFFAOYSA-N Y

* InChI=1/C.Hf/q-1;+1/rCHf/c1-2

Key: NVDNLVYQHRUYJA-GLWNXBRTAK

SMILES

* [Hf+]#[C-]

Properties

Chemical formula

| HfC
Molar mass | 190.50 g/mol
Appearance  | black odorless powder
Density | 12.2 g/cm3[1]
Melting point |  3,900 °C (7,050 °F; 4,170 K)[2]

Solubility in water

| insoluble
Structure

Crystal structure

| Cubic crystal system, cF8

Space group

| Fm3m, No. 225
Hazards

EU classification (DSD) (outdated)

| not listed
NFPA 704 (fire diamond)  |

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)
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] This compound may be seen on future spacecraft as part of the heat shield.

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 (>9 Mohs[5]) 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.[6]

## 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. ↑ 2.0 2.1 2.2 Harry Julius Emeléus (1968). Advances in Inorganic Chemistry and Radiochemistry. Academic Press. pp. 169–170. ISBN 978-0-12-023611-4. https://books.google.com/books?id=-SnCsg5jM_kC&pg=PA169.
3. ↑ Shimada, Shiro (1992). "Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480o to 600oC". Journal of the American Ceramic Society 75 (10): 2671–2678. 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 (1–2): 4–10. doi:10.1016/j.jallcom.2007.08.018.
5. ↑ CRC Materials Science and Engineering Handbook (2001).
6. ↑ 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 978-3-540-41817-7. https://books.google.com/books?id=jc2D7TGZcyUC&pg=PA513.

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Hafnium compounds

Hf(II)|

* HfB2

Hf(IV)|

* HfC
* HfBr4
* HfCl4
* HfF4
* HfI4
* Hf(C5H7O2)4
* HfO2
* HfSiO4
* HfS2
* Ta4HfC5

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