Tantalum hafnium carbide

Tantalum hafnium carbide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.068.426
EC Number
  • 275-291-2
  • InChI=1S/5C.Hf.4Ta
    Key: SWQWZVPEXQVZCJ-UHFFFAOYSA-N
  • [C].[C].[C].[C].[C].[Hf].[Ta].[Ta].[Ta].[Ta]
Properties
Ta4HfC5
Melting point 3,905 °C; 7,061 °F; 4,178 K
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tantalum hafnium carbide is a refractory chemical compound with a general formula Tax Hfy-x Cy, which can be considered as a solid solution of tantalum carbide and hafnium carbide. It was originally thought to have the highest melting of any known substance but new research has proven that hafnium carbonitride has a higher melting point.

Properties

Individually, tantalum and hafnium carbide have the highest melting points among the binary compounds, 4,041 K (3,768 °C; 6,814 °F) and 4,232 K (3,959 °C; 7,158 °F), respectively,[1] and their "alloy" with a composition Ta4HfC5 has a melting point of 4,178 K (3,905 °C; 7,061 °F).[2]

Very few measurements of melting point in tantalum hafnium carbide have been reported, because of the obvious experimental difficulties at extreme temperatures. A 1965 study of the TaC-HfC solid solutions at temperatures 2,225–2,275 °C found a minimum in the vaporization rate and thus maximum in the thermal stability for Ta4HfC5. This rate was comparable to that of tungsten and was weakly dependent on the initial density of the samples, which were sintered from TaC-HfC powder mixtures, also at 2,225–2,275 °C. In a separate study, Ta4HfC5 was found to have the minimum oxidation rate among the TaC-HfC solid solutions.[3] Ta4HfC5 was manufactured by Goodfellow company as a 45 µm powder[4] at a price of $9,540/kg (99.0% purity).[5]

In 2015, atomistic simulations predicted that hafnium carbonitride could have a melting point exceeding Ta4Hf1C5 by 200 K.[6] This was later verified by experimental evidence in 2020.[7]

Structure

Individual tantalum and hafnium carbides have a rocksalt cubic lattice structure. They are usually carbon deficient and have nominal formulas TaCx and HfCx, with x = 0.7–1.0 for Ta and x = 0.56–1.0 for Hf. The same structure is also observed for at least some of their solid solutions.[8] The density calculated from X-ray diffraction data is 13.6 g/cm3 for Ta0.5Hf0.5C.[9][10] Hexagonal NiAs-type structure (space group P63/mmc, No. 194, Pearson symbol hP4) with a density of 14.76 g/cm3 was reported for Ta0.9Hf0.1C0.5.[9]

See also

References
  1. 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.
  2. "New record set for world's most heat resistant material".
  3. Deadmore, D. L. (1965). "Vaporization of Tantalum Carbide-Hafnium Carbide Solid Solutions". Journal of the American Ceramic Society. 48 (7): 357–359. doi:10.1111/j.1151-2916.1965.tb14760.x. Archived from the original on 27 March 2012.
  4. Goodfellow catalogue, February 2009, p. 102
  5. NIAC 7600-039 FINAL REPORT, NASA Institute for Advanced Concepts – A Realistic Interstellar Explorer, 14 October 2003, p. 55
  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. 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.
  9. Rudy, E.; Nowotny, H. (1963). "Untersuchungen im System Hafnium-Tantal-Kohlenstoff". Monatshefte für Chemie. 94 (3): 507–517. doi:10.1007/BF00903490.
  10. Rudy, E.; Nowotny, H.; Benesovsky, F.; Kieffer, R.; Neckel, A. (1960). "Über Hafniumkarbid enthaltende Karbidsysteme". Monatshefte für Chemie. 91: 176–187. doi:10.1007/BF00903181.
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