Gas Permeability and Bending Strength of Porous SiC Ceramics

Abstract

The reaction-sintered porous SiC ceramics with different particle sizes and porosities are prepared, and the effects of particle size and porosity on their gas permeability and bending strength are investigated. For porosities above 0.25, the Ergun's equation well explains the small pressure drop at large particle sizes and high porosities which were achieved by the decreased compaction pressure of raw materials. The reduction in porosity down to 0.26 by the addition of free Si under the constant compaction pressure increased the bending strength remarkably, while no change in the pressure drop was accompanied. At a porosity smaller than 0.26, an abrupt increase of the pressure drop was observed without any further increase in bending strength. These observations were examined through the analysis of morphology and pore size distribution. The abrupt change was found to occur at the point where all the smaller pores are filled with Si completely. The preferential filling of Si in smaller pores can be explained by the good wetting of SiC with Si.