Synthesis and thermo-mechanical properties of mullite–alumina composite derived from sillimanite beach sand: effect of ZrO 2

Abstract

A mullite–alumina composite was developed by reaction sintering of sillimanite beach sand and calcined alumina. ZrO 2 (2–6 wt.%) was added as additive. The raw materials and additive were mixed, attrition milled and sintered in compacted form at 1400–1600°C with 2 h soaking. The effect of ZrO 2 on the densification behaviour, thermo-mechanical properties and microstructure was studied. It was found that addition of ZrO 2 slightly retards the densification process. All the samples achieved their highest bulk density at 1600°C. Thermo-mechanical properties of the sintered samples are not effectively altered by the presence of ZrO 2. ZrO 2 containing samples always show better resistance to thermal shock than the ZrO 2 free samples. Scanning electron micrography shows that ZrO 2 occupies both an intergranular and intragranular position in the mullite matrix. The mullite formed at 1600°C is mostly equiaxed in nature that suggests densification mainly occurs through solid state sintering.