Oxidation Resistance, Compressive Strength and Thermal Shock Resistance of SiC Ceramics Prepared by Two Processing Routes

Abstract

In the present paper, direct foaming technique and sacrificial template method were used to prepare porous alumino-silicate bonded SiC ceramics from mixtures of silicon carbide, kaolin and calcined alumina. The direct foaming process depends on generating bubbles inside the slurry of SiC mixtures through a reaction between CaC2 and Al powder in presence of H2O to form C2H2 and H2 gases in two steps of the reaction. In the sacrificial template method, the pores were created in the prepared SiC specimens after burning out the used sacrificial template, corn and potato starch. Some fired specimens were selected to study the effect of their composition and preparation conditions on their oxidation resistivity, compressive strength and thermal shock resistivity. Based on purity and homogenous microstructure, the present study offers SiC specimens with good oxidation resistance where they exhibit (0.1 to 2 mg/cm2) increase in mass after oxidation in air at a temperature of 1100 C for 65 h, despite their high open porosity values. The present SiC specimens have high thermal shock resistivity. However, the foamed specimens showed better resistivity than those prepared by the sacrificial template method. Using the extruder for shaping the latter specimens improves their resistivity to thermal shock. The compressive strength of both groups of specimens is affected by their composition and preparation conditions.