Theoretical and experimental analyses of relationship between processing and thermal conductivity of SiC with oxide additives

This paper analyzes theoretically and experimentally the thermal conductivity of the SiC-oxide additive-pore system. In the developed 6 model structures, the thermal conductivity of an SiC compact (κb) with oxide was calculated as functions of the volume fractions of SiC, oxide additive and pores. The calculated κb decreases in the order of a continuous phase where the other two particulate phases are dispersed: SiC>oxide additive>pores. The measured κb values of SiC compacts hot-pressed with 4–50 mass% oxide additive (mixture of 33.3 mass% Al2O3-33.3 mass% Y2O3-33.3 mass% SiO2) were well explained by the calculated κb in two types of oxide continuous phase models. The thermal conductivities for only SiC grains in SiC compacts hot-pressed with 4 mass% Al2O3, Y2O3, SiO2, Al2O3-Y2O3, Y2O3-SiO2 and Al2O3-Y2O3-SiO2 at 1950 °C were also estimated theoretically in the developed two model structures using the measured κb (oxide continuous phase model and SiC continuous phase model). Based on the calculated results, the following key factors are identified to achieve a high κb: (1) high sintered density, (2) a small amount of oxide additive with a high thermal conductivity, (3) no dissolution of foreign atoms from a liquid phase into SiC grains during solidification process.