Thermal Properties and Elastic Constants of ζ-Ta₄C₃₋ₓ

Thermal and elastic properties were measured for ceramics that contained as much as 96 wt% zeta phase tantalum carbide (ζ-Ta4C3-x). The ceramics were produced from tantalum hydride that was milled to reduce particle size and then blended with carbon. Powders were reaction hot-pressed at 1800°C for 2 hours under a flowing He environment, which resulted in ζ-Ta4C3-x that was about 99% dense. The main secondary phases present in the reacted ceramic were TaC and Ta2O5. ζ-Ta4C3-x had a thermal conductivity of 9.6 W/m·K and an electrical resistivity of 160 ± 4.2Â µΩ-cm, which are lower and higher than those of TaC, respectively. The Young\u27s modulus was 379 ± 5 GPa and the hardness was 5.1 ± 0.7 GPa, which are also both lower than TaC. This study is the first to report the thermal properties and elastic moduli of high-purity ζ-Ta4C3-x

Thermal and Electrical Properties of a High Entropy Carbide (Ta, Hf, Nb, Zr) at Elevated Temperatures

The thermal and electrical properties were measured for a high entropy carbide ceramic, consisting of (Hf, Ta, Zr, Nb)C. The ceramic was produced by spark plasma sintering a mixture of the monocarbides and had a relative density of more than 97.6%. The resulting ceramic was chemically homogeneous as a single-phase solid solution formed from the constituent carbides. The thermal diffusivity (0.045-0.087 cm2/s) and heat capacity (0.23-0.44 J/g·K) were measured from room temperature up to 2000°C. The thermal conductivity increased from 10.7 W/m·K at room temperature to 39.9 W/m·K at 2000°C. The phonon and electron contributions to the thermal conductivity were investigated, which showed that the increase in thermal conductivity was predominantly due to the electron contribution, while the phonon contribution was independent of temperature. The electrical resistivity increased from 80.9 μΩ·cm at room temperature to 114.1 μΩ·cm at 800°C