Effect of Al(OH)3 addition on densification mechanism and properties of reaction-sintered mullite-corundum composite ceramics

ABSTRACT Mullite composite ceramics were fabricated by using mullite powder from waste coal gangue and Al(OH)3 as starting materials. The effects of sintering temperature and Al(OH)3 content on phase composition, microstructure, and mechanical properties of the ceramics were systematically investigated. Results show that the bulk density and flexural strength of composite ceramics increase as the temperature increases from 1480°C to 1560°C. The composite ceramics exhibit optimal performances with addition of 10 wt.% Al(OH)3 at 1560°C, a bulk density of 2.43 g/cm3 and a flexural strength of 124.28 MPa, respectively. Moreover, additional Al(OH)3 promotes a reaction between SiO2 and Al2O3 and forms more mullite phase. The increase in mullite content endows the composite ceramics with high mechanical properties. Scanning electron microscope images indicate that the mullite particles exhibit an interlocking structure, while the corundum phase is “pinned” within the mullite interlocking structure, contributing to the mechanical properties of composite ceramics.