Effect of phase composition on thermal and electrical conductivity of additive-free silicon carbide ceramics

Dense (RD > 97%) silicon carbide ceramics without any sintering additives were prepared by freeze granulation of silicon carbide powders, annealing of granulated powders and subsequent densification by field assisted sintering technique (FAST) at 1900 degrees C. Thermal and electrical conductivity of prepared materials considering the mass fraction of SiC polytypes was investigated. Different ratio of alpha and beta silicon carbide has been achieved by adjusting dwell time during sintering. Thermal diffusivity, specific heat capacity, thermal conductivity, electrical conductivity, density, microstructure of additive-free SiC with various alpha/beta content has been investigated. The electrical conductivity of SiC ceramics decrease from 104 S/m to 8 S/m as a content of alpha-SiC increase from 63 % to 94 %. Opposite trend, when thermal diffusivity increased from 47.3 to 69.9 mm(2)/s as a content of alpha-SiC increase from 63 % to 94%, was observed. The highest thermal conductivity (lambda=165 W/m.K) among the SiC ceramics sintered at temperatures <= 1900 degrees C was achieved for additive-free SiC sintered at 1900 degrees C under vacuum for 80 minutes.