Influence of sintering atmosphere and BN additives on microstructure and properties of porous SiC ceramics

The effects of the boron nitride (BN) content on the electrical, thermal, and mechanical properties of porous SiC ceramics were investigated in N2 and Ar atmospheres. The electrical resistivity was predominantly controlled by the sintering atmosphere and secondarily by the BN concentration, whereas the thermal conductivity and flexural strength were more susceptible to changes in the porosity and necking area between the SiC grains. The electrical resistivities of argon-sintered porous SiC ceramics (6.3 x 105 - 1.6 x 106 omega center dot cm) were seven orders of magnitude higher than those of nitrogen-sintered porous SiC ceramics (1.5 x 10-1 - 6.0 x 10-1 omega center dot cm). The thermal conductivity and flexural strength of the argon-sintered porous SiC ceramics increased from 8.4-11.6 W center dot m- 1 K-1 and from 9.3-28.2 MPa, respectively, with an increase in the BN content from 0 to 1.5 vol %, which was attributed to the increase in necking area and the decrease in porosity.