Influence of starting materials on the reaction sintering of mullite–ZrO2 composites

Mullite–zirconia composite materials were prepared by reaction sintering of α-alumina, aluminium hydroxide and aluminium nitrate as alumina sources, and zircon powder. The compaction of different calcined powders, and the reaction development, densification behaviour and microstructural investigations of different samples were examined at temperatures ranging from 1350 to 1600°C for 2 h holding time. X-ray diffraction peaks suggested fully developed mullite and zirconia phases by reaction sintering of zircon and aluminium nitrate, and showed more retained tetragonal ZrO2 at 1600°C. Relatively dense sintered samples were obtained by the mixture of zircon and α-alumina powders. The morphology of intergranular ZrO2 particles was found dependent on the growing conditions because of the using of different starting materials.