Preparation and thermal shocks of mullite‐based porous ceramic materials using the reaction sintering method

Abstract Mullite‐based porous ceramics are characterized by high strength, good high‐temperature resistance, and excellent thermal shock resistance. In this paper, coal gangue‐based mullite porous ceramics were prepared by the reaction sintering method. The effects of gangue addition on the density, phase composition, microstructure, and thermal shock resistances of the samples were evaluated. The results showed that the introduction of gangue significantly improved the porous microstructure and the thermal shock resistance. After firing at 1640°C, the D1 sample (50 wt% Al 2 O 3 , 50 wt% gangue) presented the best comprehensive properties, and it displayed a slight decrease in bending strength after 20 thermal shock cycles. The porous microstructure of samples was associated with the development of needle‐like secondary mullite via dissolution of Al 2 O 3 grain into the silica‐rich liquid phase at high temperature. With a descending in gangue addition, the sintering behavior of Al 2 O 3 grains instead affected the microstructural densification. The formation of needle‐shaped mullite, combined with the resulting decreased thermal expansion coefficient improved the thermal shock resistance. The as‐prepared porous ceramics are advantageous for high strength and good thermal shock resistance, in spite of the low porosity.