Hafnium carbonitride

Hafnium carbonitride (HfCN) is an ultra-high temperature ceramic (UHTC) mixed anion compound composed of hafnium (Hf), carbon (C) and nitrogen (N).

Hafnium carbonitride

Identifiers
3D model (JSmol)	Interactive image
InChI InChI=1S/C.2Hf.N Key: MANOWAVKGDAAGH-UHFFFAOYSA-N
SMILES [Hf].[Hf].[C].[N]
Properties
Chemical formula	CHf2N
Molar mass	204.51 g/mol[1]
Appearance	black odorless powder
Density	12.65–13.073 g/cm3[2]
Melting point	4,110 °C (7,430 °F; 4,380 K)[3]
Solubility in water	insoluble
Thermal conductivity	19–24 W⋅m−1⋅K−1[2]
Structure
Crystal structure	Cubic crystal system, cF8
Space group	Fm3m, No. 225
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Ab initio molecular dynamics calculations have predicted the HfCN (specifically the HfC_0.75N_0.22 phase) to have a melting point of 4,110 ± 62 °C (4,048–4,172 °C, 7,318–7,542 °F, 4,321–4,445 K),^[3] the highest known for any material.^[3][4][5] Another approach based on the artificial neural network machine learning pointed towards a similar composition — HfC_0.76N_0.24.^[3] Experimental testing conducted in 2020 has confirmed a melting point above 4,000 °C (7,230 °F; 4,270 K),^[4][5] substantiating earlier predictions made with atomistic simulations in 2015.^[6]

Properties

The HfC_xN_1−x has been assessed to possess the following properties:^[2]

• Thermal conductivity:
  • 19–24 W·m⁻¹·K⁻¹ at room temperature,
  • 32–39 W·m⁻¹·K⁻¹ at high temperature and with increased nitrogen content.
• Electrical conductivity: (149×10⁴)–(213×10⁴) Ω⁻¹ m⁻¹
• Plasticity limit: 2,000 °C (3,630 °F; 2,270 K)^[a]
• Fusion enthalpy: 150 kJ/mol (36 kcal/mol)^[3]
• Flexural strength:^[b]
  • 638 ± 28 MPa at room temperature,
  • 324 MPa at 1,000 °C (1,830 °F; 1,270 K),
  • 139 MPa at 1,600 °C (2,910 °F; 1,870 K),
  • 100 MPa at 2,000 °C (3,630 °F; 2,270 K).
• Fracture toughness: 6.73 ± 0.07 MPa·m^1/2[a], 4.7 ± 0.3 MPa·m^1/2[c][4]
• Vickers hardness: 19.08 GPa (2,767,000 psi)^[b], 21.3 ± 0.55 GPa (3,090,000 psi)^[c][4]

1. For HfC_0.3N_0.7
2. For HfC_0.7N_0.3
3. For HfC_0.5N_0.35