Intermediate Si-Al spinel phase formation in phase transformation of diphasic mullite gel

Abstract

Al2O3-SiO2 diphasic mullite gel (Si/Al=1/3) has been synthesized by using Al(NO3)3·9H2O and Ludox in basic conditions. Its phase transformation behaviour has been studied by qualitative and quantitative X-ray diffraction techniques. The results indicate that a noncrystalline alumino-silicate phase forms together with the slow crystallization of Si-Al spinel phase of a mullite-like composition up to 1250 °C. Thereafter, it transforms suddenly to orthorhombic mullite around 1325 °C. Earlier studies, e.g. alkali leaching, and measurement of co-ordination number of aluminium in 1000 °C heated diphasic gel, confirm Si-Al spinel formation as an intermediary phase.