Processing and thermal properties of an Mo₅Si₃C-SiC ceramic

Composite ceramics containing ∼25 vol% of the Mo-Si-C ternary compound and SiC (referred to as MS) were reaction hot pressed up to 96% relative density. The electrical resistivity of the composite processed at 2150 °C decreased from ∼4.60 Ω cm at room temperature to 4.15 Ω cm at 700 °C. Thermal conductivity of the MS ceramics processed at 2150 °C was above 100 W/m K at room temperature, decreasing to between 62 and 68 W/m K at 500 °C. Using the Eucken model for thermal conductivity, the interconnected SiC phase in the MS materials was calculated to have a room temperature thermal conductivity between 160 and 170 W/m K. As compared to a baseline SiC composition, the continuous SiC in the MS materials had an average increase in thermal conductivity of ∼50% over the temperature range of room temperature to 500 °C. This increase in thermal conductivity was attributed to the accommodation of impurities that would typically be present in SiC grains and grain boundaries (e.g., N and O) into the ternary phase.