tantalum hafnium carbide
{{Use dmy dates|date=September 2021}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 448727871
| Name = Tantalum hafnium carbide
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| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 71243-79-3
| EINECS = 275-291-2
| SMILES = [C].[C].[C].[C].[C].[Hf].[Ta].[Ta].[Ta].[Ta]
| StdInChI=1S/5C.Hf.4Ta
| StdInChIKey = SWQWZVPEXQVZCJ-UHFFFAOYSA-N
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| Section2 = {{Chembox Properties
| Formula = {{chem2|Ta4HfC5}}
| Ta=4|Hf=1|C=5
| Density =
| MeltingPtK = 4178
| BoilingPt =}}
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Tantalum hafnium carbide is a refractory chemical compound with a general formula {{chem2|Ta_{x}Hf_{y}C_{x+y}|auto=1}}, 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{{cite journal | author1=Andrievskii, R.A. | author2=Strel'nikova, N.S. |author3=Poltoratskii, N.I. |author4=Kharkhardin, E.D. | author5=Smirnov, V.S. | title=Melting point in systems ZrC-HfC, TaC-ZrC, TaC-HfC | journal=Powder Metall Met Ceram | volume=6 |pages=65–67 |year=1967 |doi=10.1007/BF00773385}} but new research has proven that hafnium carbonitride has a higher melting point.
Properties
Individually, the tantalum and hafnium carbides have the highest melting points among the binary compounds, {{convert|4041|K}} and {{convert|4232|K}}, respectively,{{cite journal | doi=10.1038/srep37962 | title=Investigating the highest melting temperature materials: A laser melting study of the TaC-HFC system | year=2016 | last1=Cedillos-Barraza | first1=Omar | last2=Manara | first2=Dario | last3=Boboridis | first3=K. | last4=Watkins | first4=Tyson | last5=Grasso | first5=Salvatore | last6=Jayaseelan | first6=Daniel D. | last7=Konings | first7=Rudy J. M. | last8=Reece | first8=Michael J. | last9=Lee | first9=William E. | journal=Scientific Reports | volume=6 | page=37962 | pmid=27905481 | pmc=5131352 | bibcode=2016NatSR...637962C }} and their "alloy" with a composition {{chem2|Ta4HfC5}} has a melting point of {{convert|4178|K}}.{{cite web | url=https://phys.org/news/2016-12-world-resistant-material.html | title=New record set for world's most heat resistant material }}
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 {{chem2|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, {{chem2|Ta4HfC5}} was found to have the minimum oxidation rate among the TaC-HfC solid solutions.{{cite journal|url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA396947|archive-url=https://web.archive.org/web/20120327064834/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA396947|url-status=dead|archive-date=27 March 2012|title=Vaporization of Tantalum Carbide-Hafnium Carbide Solid Solutions|doi=10.1111/j.1151-2916.1965.tb14760.x|year=1965|last1=Deadmore|first1=D. L.|journal=Journal of the American Ceramic Society|volume=48|issue=7|pages=357–359}} {{chem2|Ta4HfC5}} was manufactured by Goodfellow company as a 45 μm powder[http://www.furuchi.co.jp/material/img/goodfellow_catalog.pdf Goodfellow catalogue], February 2009, p. 102 at a price of $9,540/kg (99.0% purity).[http://www.niac.usra.edu/files/studies/final_report/393McNutt.pdf NIAC 7600-039 FINAL REPORT], NASA Institute for Advanced Concepts – A Realistic Interstellar Explorer, 14 October 2003, p. 55
In 2015, atomistic simulations predicted that hafnium carbonitride could have a melting point exceeding {{chem2|Ta4HfC5}} by 200 K.{{cite journal|last1=Hong|first1=Qi-Jun|last2=van de Walle|first2=Axel|year=2015|title=Prediction of the material with highest known melting point from ab initio molecular dynamics calculations|journal=Physical Review B|volume=92|issue=2|page=020104|doi=10.1103/PhysRevB.92.020104|bibcode=2015PhRvB..92b0104H|issn=1098-0121|doi-access=free}} This was later verified by experimental evidence in 2020.{{cite web | url=https://www.forbes.com/sites/allisongasparini/2020/05/31/scientists-create-worlds-most-heat-resistant-material-with-potential-use-for-spaceplanes/?sh=79f5452b4f7e | title=Scientists Create World's Most Heat Resistant Material with Potential Use for Spaceplanes | website=Forbes }}
Structure
Individual tantalum and hafnium carbides have a rocksalt cubic lattice structure. They are usually carbon deficient and have nominal formulas {{chem2|TaC_{x}|}} and {{chem2|HfC_{x}|}}, 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.{{cite journal|last1=Lavrentyev|first1=A|last2=Gabrelian|first2=B|last3=Vorzhev|first3=V |last4=Nikiforov|first4=I|last5=Khyzhun|first5=O|last6=Rehr|first6=J|year=2008|title=Electronic structure of cubic HfxTa1–xCy carbides from X-ray spectroscopy studies and cluster self-consistent calculations|journal=Journal of Alloys and Compounds |volume=462 |issue=1–2|pages=4–10|doi=10.1016/j.jallcom.2007.08.018}} The density calculated from X-ray diffraction data is 13.6 g/cm3 for {{chem2|Ta0.5Hf0.5C}}.{{cite journal|doi=10.1007/BF00903490 |title= Untersuchungen im System Hafnium-Tantal-Kohlenstoff|year=1963 |last1=Rudy|first1=E. |last2=Nowotny|first2=H. |journal=Monatshefte für Chemie|volume=94|issue=3|pages=507–517}}{{cite journal|doi= 10.1007/BF00903181 |title=Über Hafniumkarbid enthaltende Karbidsysteme |year=1960|last1=Rudy|first1=E.|last2=Nowotny |first2=H.|last3=Benesovsky|first3=F. |last4=Kieffer|first4=R. |last5=Neckel|first5=A.|journal=Monatshefte für Chemie|volume=91|pages=176–187}} Hexagonal NiAs-type structure (space group P63/mmc, No. 194, Pearson symbol hP4) with a density of 14.76 g/cm3 was reported for {{chem2|Ta0.9Hf0.1C0.5}}.
See also
References
{{reflist}}
{{tantalum compounds}}
{{hafnium compounds}}