Thermal Conductivity of SiC_f  /SiC Composites at Elevated Temperature

Abstract

Silicon carbide fiber reinforced silicon carbide composites (SiC_f/SiC composites) are one of the candidate materials for fusion reactors such as first wall and divertor due to their low activation, mechanical and chemical stability at elevated tem­perature. SiC_f/SiC composites are required high thermal conductivity at elevated temperature to reduce heat load and to provide high thermal conversion efficiency. The purposes of this study are development of SiC_f/SiC composites and determine of the thermal conductivity at elevated temperature. SiC_f/SiC composites were fabricated by hot-press method. Sintering temperature and pressure of SiC_f/SiC composites were 1,900°C and 20 MPa. Tyranno-SA fibers were used as reinforce materials.The bulk density of fabricated SiC_f/SiC composites was measured by the Archimedes method with an immersion medium of distilled water. Thermal conductivity was calculated from the measured bulk density, thermal diffusivity and specific heat capacity. Thermal diffusivities and specific heat capacities of SiC_f/SiC composites were measured by the laser flash method using a thermal analyzer. Thermal conductivity of SiC_f/SiC composites in vacuum was measured temperature ranging from 25 to 1,200°C. The thermal conductivity of fabricated SiC_f/SiC composites at room temperature was approximately 60 W/mK. The lower dense materials such as CVI-SiC/SiC composites have low thermal conductivity approximately 15 W/mK at room temperature due to high porosity in composites despite high thermal conductivity of matrix. But, the fabricated SiC_f/SiC composites have high thermal conductivity due to densification and high thermal conductive matrix. Thermal conductivity of SiC_f/SiC composites deceased with increasing temperature, since the frequency of phonon scattering increases with increasing temperature.