Electrical, thermal, and mechanical properties of porous silicon carbide ceramics with a boron carbide additive

The effects of the boron carbide (B4C) content and sintering atmosphere on the electrical, thermal, and mechanical properties of porous silicon carbide (SiC) ceramics were investigated in the porosity range of 58.3%-70.3%. The electrical resistivities of the nitrogen-sintered porous SiC ceramics (similar to 10(-1) omega center dot cm) were two orders of magnitude lower than those of argon-sintered porous SiC ceramics (similar to 10(1) omega center dot cm). Both the thermal conductivities (3.3-19.8 W center dot m(-1)center dot K-1) and flexural strengths (8.1-32.9 MPa) of the argon- and nitrogen-sintered porous SiC ceramics increased as the B4C content increased, owing to the decreased porosity and increased necking area between SiC grains. The electrical resistivity of the porous SiC ceramics was primarily controlled by the sintering atmosphere owing to the N-doping from the nitrogen atmosphere, and secondarily by the B4C content, owing to the B-doping from the B4C. In contrast, the thermal conductivity and flexural strength were dependent on both the porosity and necking area, as influenced by both the sintering atmosphere and B4C content. These results suggest that it is possible to decouple the electrical resistivity from the thermal conductivity by judicious selection of the B4C content and sintering atmosphere.