Elevated temperature thermal and electrical properties of carbon nanotubes, graphite and graphene reinforced (Zr-Ta-W-Ti)C-SiC based high entropy carbide ceramics

High temperature thermal conductivity up to 1200 degrees C and the electrical conductivity up to 800 degrees C were studied for (Zr-Ta-W-Ti)C-SiC (ZTaWT-S) based high entropy carbide ceramics containing carbonaceous reinforcements (multi-walled carbon nanotubes (CNT), graphite flakes (G), and graphene nanoplatelets (GNP). The thermal diffusivity (0.055-0.067 cm(-2)s) and specific heat capacity (0.38-0.44 Jg(-1)K(-1)) were experimentally measured from 50 degrees C to 1200 degrees C for all the composites. The thermal conductivity of the composites lies in the range of 18.2 Wm(-1)K(-1) to 22.9 Wm(-1)K(-1) for the temperature range of 50 degrees C-1200 degrees C, from the significant phonon scattering at the interfaces of the elements of different size and atomic masses. At 50 degrees C, the limited thermal conductivity enhancement for carbonaceous reinforcements from 18.2 Wm(-1)K(-1) for ZTaWT-S to 21.0 Wm(-1)K(-1) for ZTaWT-SC (CNT reinforcement) to 20.8 Wm(-1)K(-1) for ZTaWT-SG (graphite reinforcement), and to 19.9 Wm(-1)K(-1) ZTaWT-SGNP (graphene reinforcement) is attributed to the high thermal resistance at the interfaces between different phases and interface with carbon additives, evident in the TEM investigation of the crushed sintered sample, and at the grain boundaries (interfacial thermal resistance). The phonon and electron contribution to thermal conductivity were also assessed and the kappa(e)/kappa(exp) ratio analysis confirms the predominant role of phonon contribution to thermal conductivity (similar to 65%) at low temperature (similar to 50 degrees C) and of electronic contribution at high temperatures (similar to 800 degrees C) as the dominant mechanism of thermal transport in the investigated composites and ZTaWT-SGNP composite with the highest kappa(e)/kappa(exp) ratio of 0.84 (extrapolated) emerges as the most electronically conductive material.