Effects of Additives on Thermal Conductivity and Electrical Resistivity of SiC Ceramics

Abstract

Effects of various additives on densification, thermal conductivity and electrical resistivity of SiC ceramics were studied. Addition of elemental Be, B and Al or their compounds gave higher-than-98% theoretical densities by hot-pressing at 2040°C for 1h at a load of 20MPa. Thermal conductivity and electrical resistivity of dense SiC ceramics were measured at 25°C. They depend largely on the additives. SiC ceramics containing Be or its compounds had high thermal conductivity of above 260W/m·K and electrical resistivity of above 1×1013Ω·cm. On the other hand, SiC ceramics containing B or its compounds had thermal conductivity of 110-170W/m·K and electrical resistivity of 104-1011Ω·cm. Al or its compounds gave the lowest thermal conductivity and electirical resistivity of 60-80W/m·K and 0.6-27Ω·cm, respectively. Thermal conductivity and electrical resistivity of SiC ceramics depend on the amount of impurities and free carrier concentration in the SiC grains. The effects of additives on thermal conductivity and electrical resistivity of SiC ceramics examined were attributed to the different solubilities of the additives into SiC grains. High thermal conductivity and high electrical resistivity of SiC ceramics containing Be or its compounds were shown to be caused by low solubility of Be into SiC grains.