Chemistry:Hafnium carbide

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Hafnium carbide
Hafnium carbide
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 235-114-1
Properties
HfC
Molar mass 190.50 g/mol
Appearance black odorless powder
Density 12.2 g/cm3[1]
Melting point 3,958 °C (7,156 °F; 4,231 K)[2]
insoluble
Structure
Cubic crystal system, cF8
Fm3m, No. 225
Hazards
GHS pictograms GHS02: Flammable
GHS Signal word Warning
H228
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no codeNFPA 704 four-colored diamond
2
2
1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is ☑Y☒N ?)
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.[2] 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.[3] However, it has a low oxidation resistance, with the oxidation starting at temperatures as low as 430 °C.[4] 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.[5]

Atomistic simulations conducted in 2015 predicted that a Hf-C-N material could have a melting point exceeding even that of hafnium carbide.[6] More recent experimental evidence gathered in 2020 confirmed that hafnium carbonitride did indeed have a higher melting point exceeding 4,000 °C.[7]

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.[8]

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[9]) 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.[10]

See also

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). "Metal Carbides". 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. ↑ Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J. et al. (2016). "Investigating the highest melting temperature materials: A laser melting study of the TaC-HFC system". Scientific Reports 6: 37962. doi:10.1038/srep37962. PMID 27905481. Bibcode: 2016NatSR...637962C. 
  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. doi:10.3390/ma12172728. PMID 31454900. Bibcode: 2019Mate...12.2728U. 
  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. doi:10.1103/PhysRevB.92.020104. ISSN 1098-0121. Bibcode: 2015PhRvB..92b0104H. 
  7. ↑ "Scientists Create World's Most Heat Resistant Material with Potential Use for Spaceplanes". https://www.forbes.com/sites/allisongasparini/2020/05/31/scientists-create-worlds-most-heat-resistant-material-with-potential-use-for-spaceplanes/?sh=79f5452b4f7e. 
  8. ↑ Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya.; Khyzhun, O.Yu.; Rehr, J.J. (2008-08-26). "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. 
  9. ↑ CRC Materials Science and Engineering Handbook (3rd ed.). CRC Press. 2001. ISBN 978-0-849-32696-7. 
  10. ↑ 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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