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Hafnium carbide

Identifiers
CAS Number	12069-85-1
3D model (JSmol)	Interactive image
ChemSpider	17340381
ECHA InfoCard	100.031.910
EC Number	235-114-1
PubChem CID	16212551
CompTox Dashboard (EPA)	DTXSID501027098 DTXSID00923528, DTXSID501027098
InChI InChI=1S/C.Hf/q-1;+1Key: NVDNLVYQHRUYJA-UHFFFAOYSA-N InChI=1/C.Hf/q-1;+1/rCHf/c1-2Key: NVDNLVYQHRUYJA-GLWNXBRTAK
SMILES #
Properties
Chemical formula	HfC
Molar mass	190.50 g/mol
Appearance	black odorless powder
Density	12.2 g/cm
Melting point	3,958 °C (7,156 °F; 4,231 K)
Solubility in water	insoluble
Structure
Crystal structure	Cubic crystal system, cF8
Space group	Fm3m, No. 225
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H228
NFPA 704 (fire diamond)	2 2 1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). N verify (what is  ?) Infobox references

Hafnium carbide (HfC) is a chemical compound of hafnium and carbon. Previously the material was estimated to have a melting point of about 3,900 °C. More recent tests have been able to conclusively prove that the substance has an even higher melting point of 3,958 °C exceeding those of tantalum carbide and tantalum hafnium carbide which were both previously estimated to be higher. However, it has a low oxidation resistance, with the oxidation starting at temperatures as low as 430 °C. Experimental testing in 2018 confirmed the higher melting point yielding a result of 3,982 (±30°C) with a small possibility that the melting point may even exceed 4,000°C.

Atomistic simulations conducted in 2015 predicted that a similar compound, hafnium carbonitride (HfCN), could have a melting point exceeding even that of hafnium carbide. Experimental evidence gathered in 2020 confirmed that it did indeed have a higher melting point exceeding 4,000 °C, with more recent ab initio molecular dynamics calculations predicting the HfC_0.75N_0.22 phase to have a melting point as high as 4,110 ± 62 °C, highest known for any material.

Hafnium carbide is usually carbon deficient and therefore its composition is often expressed as HfC_x (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 1,800 to 2,000 °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 (greater than 9 Mohs) and melting point.

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

See also

• Tantalum carbide
• Tantalum hafnium carbide
• Hafnium carbonitride

References

1. Physical Constants of Inorganic Compounds in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton, Florida: CRC Press. pp. 4–44 ff. ISBN 0-8493-0486-5.
2. ^ Harry Julius Emeléus (1968). "Metal Carbides". Advances in Inorganic Chemistry and Radiochemistry. Academic Press. pp. 169–170. ISBN 978-0-12-023611-4.
3. Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E. (2016). "Investigating the highest melting temperature materials: A laser melting study of the TaC-HFC system". Scientific Reports. 6: 37962. Bibcode:2016NatSR...637962C. doi:10.1038/srep37962. PMC 5131352. PMID 27905481.
4. Shimada, Shiro (October 1992). "Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480° to 600°C". Journal of the American Ceramic Society. 75 (10): 2671–2678. doi:10.1111/j.1151-2916.1992.tb05487.x.
5. Ushakov, Sergey V.; Navrotsky, Alexandra; Hong, Qi-Jun; van de Walle, Axel (26 August 2019). "Carbides and Nitrides of Zirconium and Hafnium". Materials. 12 (17): 2728. Bibcode:2019Mate...12.2728U. doi:10.3390/ma12172728. PMC 6747801. PMID 31454900.
6. Hong, Qi-Jun; van de Walle, Axel (2015). "Prediction of the material with highest known melting point from ab initio molecular dynamics calculations". Physical Review B. 92 (2): 020104. Bibcode:2015PhRvB..92b0104H. doi:10.1103/PhysRevB.92.020104. ISSN 1098-0121.
7. "Scientists Create World's Most Heat Resistant Material with Potential Use for Spaceplanes". Forbes.
8. Dai, Yu; Zeng, Fanhao; Liu, Honghao; Gao, Yafang; Yang, Qiaobin; Chen, Meiyan; Huang, Rui; Gu, Yi (15 October 2023). "Controlled nitrogen content synthesis of hafnium carbonitride powders by carbonizing hafnium nitride for enhanced ablation properties". Ceramics International. 49 (20): 33265–33274. doi:10.1016/j.ceramint.2023.08.035. eISSN 1873-3956. ISSN 0272-8842. OCLC 9997899259. S2CID 260672783.
9. Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya.; Khyzhun, O.Yu.; Rehr, J.J. (26 August 2008). "Electronic structure of cubic Hf_xTa_1–xC_y 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.
10. James F. Shackelford; William Alexander, eds. (2001). CRC Materials Science and Engineering Handbook (3rd ed.). CRC Press. ISBN 978-0-849-32696-7.
11. 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.

• Carbides
• Hafnium compounds
• Rock salt crystal structure
• Refractory materials