Oxidation resistance of Al2O3–SiC–C castables with different grades of andalusite

Highlights:• The Al₂O₃–SiC–C castables with superior oxidation resistance were prepared.• Microstructure and properties were optimized by introducing low-grade andalusite (P57).• Thermodynamic software was used to analyse the liquid phase content of andalusite.• The oxidation resistance mechanism of Al₂O₃–SiC–C castables was analyzed. -- Abstract: This work aims to investigate the effect of impurity content of andalusite on the oxidation resistance of Al₂O₃–SiC–C castables with andalusite as part of the aggregates. Two different grades of andalusite were employed in the Al₂O₃–SiC–C castables, and their oxidation resistance performances are evaluated. The results show that after firing at 1450 °C × 3 h and 10 times of thermal shock at 950°C-air cooling, the castable containing low-grade andalusite exhibits better oxidation resistance property than that containing high-grade andalusite. The phase composition, microstructure and physical performance analysis indicate that the lower grade andalusite contains more impurities, which would facilitate the liquid phase formation at high temperature. The more generated silica-rich liquid phase would fill the pores in the matrix and have a reaction with the alumina micro-powder in the matrix to form more secondary mullite. Consequently, the addition of the lower grade of andalusite would block the entry of O₂ and thus improve the oxidation resistance of the castable to a higher degree.