Preparation and properties of mullite-SiC-O′-SiAlON composites for application in cement kiln

Mullite-SiC-O′-SiAlON composites were prepared using bauxite-based homogenized mullite, silicon powder and phenolic resin as raw materials. The phase composition, microstructure and properties of samples with various Si addition calcined at 1500 °C under reducing atmosphere were investigated. The results indicated that the mullite-SiC-O′-SiAlON composites were obtained at 1500 °C in carbon embedded condition by firing Si and bauxite-based mullite mixtures. The whisker-like SiC and O′-SiAlON in the composites were formed because of the reactions between Si and C, CO or N2, and the growth of whiskers followed VS and VLS mechanisms. Both cold and high temperature strength, and thermal shock resistance of the composites increased with increase of silicon powder addition, and the optimized Si addition was 10 wt%. The improved properties at high temperature were due to the non-oxide whiskers filling in the skeleton of mullite and forming interlocking network structure as well as direct bonding between SiC whiskers and mullite, creating strengthening and toughening effects.