Fabrication of Gradient Porous SiC Ceramics with Directional Pores without Templates

Abstract

Gradient porous pure SiC ceramics with directional SiC crystals and pores were fabricated by the high-temperature recrystallization process. In this work, silicon carbide decomposed to produce the gas mixture. The flow of gas mixture along the axial direction in the porous green body induces the surface ablation, rearrangement, and recrystallization of silicon carbide grains, which leads to the formation of the aligned columnar silicon carbide crystals and tubular pores in the axial direction. The different rates of the decomposition and recrystallization of SiC in different parts of samples resulted in the formation of the gradient porosity and pore size along the axial section of sample. Si₃N₄ powder was used as a pore-former, which promotes the formation of the gradient and interconnectivity of pores. With increasing Si₃N₄ contents, the total porosity and weight loss increase while the pores size and bending strength decrease. The total porosity of samples is 38–45%, and their bending strength is 33–38 MPa.