Hafnium carbide

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Hafnium carbide
Hafnium carbide
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.031.910 Edit this at Wikidata
EC Number
  • 235-114-1
  • InChI=1S/C.Hf/q-1;+1 checkY
    Key: NVDNLVYQHRUYJA-UHFFFAOYSA-N checkY
  • InChI=1/C.Hf/q-1;+1/rCHf/c1-2
    Key: NVDNLVYQHRUYJA-GLWNXBRTAK
  • [Hf+]#[C-]
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 labelling:
GHS02: Flammable
Warning
H228
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 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 fuelInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
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 checkY☒N ?)

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 similar compound, hafnium carbonitride (HfCN), could have a melting point exceeding even that of hafnium carbide.[6] Experimental evidence gathered in 2020 confirmed that it did indeed have a higher melting point exceeding 4,000 °C,[7] with more recent ab initio molecular dynamics calculations predicting the HfC0.75N0.22 phase to have a melting point as high as 4,110 ± 62 °C, highest known for any material.[8]

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.[9]

Hafnium carbide powder is obtained by the

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[10]) and melting point.[2]

The magnetic properties of HfCx change from

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.[11]

See also

References

  1. ISBN 0-8493-0486-5
    .
  2. ^
    ISBN 978-0-12-023611-4
    .
  3. PMID 27905481
    .
  4. doi:10.1111/j.1151-2916.1992.tb05487.x
    .
  5. PMID 31454900
    .
  6. ISSN 1098-0121
    .
  7. ^ "Scientists Create World's Most Heat Resistant Material with Potential Use for Spaceplanes". Forbes.
  8. S2CID 260672783
    .
  9. doi:10.1016/j.jallcom.2007.08.018
    .
  10. ISBN 978-0-849-32696-7
    .
  11. ISBN 978-3-540-41817-7
    .
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