Effects of initial particle size on mechanical, thermal, and electrical properties of porous SiC ceramics

Abstract

The effects of initial particle size and sintering atmosphere on the compressive strength and thermal and electrical conductivities of porous SiC ceramics, fabricated using α-SiC and polycarbosilane (PCS), were investigated in the porosity range of 40–54%. Generally, the mechanical strength and thermal conductivity of a porous SiC ceramic decrease as the porosity increases. However, in this study, both the compressive strength (10.7–17.4 MPa) and thermal conductivity (0.55–0.79 W/(m·K)) of porous SiC ceramics increased as the porosity increased from 40 to 54% because of the decreased pore size (1013–218 nm) and increased bonding area per unit volume as the starting particle size decreased (35–1 μm). The influence of sintering atmosphere on the compressive strength and thermal conductivity of the porous SiC ceramics was negligible, whereas the porous SiC ceramics sintered in N2 atmosphere exhibited 4–10 times higher electrical conductivities than those of the samples sintered in Ar atmosphere, which can be attributed to N doping in the PCS-derived β-SiC. These results suggest that the mechanical, thermal, and electrical properties of porous SiC ceramics can be independently tuned to a certain extent by judiciously selecting the starting particle size and sintering atmosphere. The compressive strength, thermal and electrical conductivities, and porosity of the porous SiC ceramic processed with 35 μm particles in the N2 atmosphere were 10.7 MPa, 0.58 W/(m·K), 2.2 × 10−3 Ω−1 cm−1, and 40.3%, respectively.