Sintering and microstructural study of mullite prepared from kaolinite and reactive alumina: Effect of MgO and TiO2

Abstract

AbstractMullite ceramic was prepared using kaolinite and synthesized alumina (combustion route) by solid‐state interaction process. The influence of TiO2 and MgO additives in phase formation, microstructural evolution, densification, and mechanical strengthening was evaluated in this work. TiO2 and MgO were used as sintering additives. According to the stoichiometric composition of mullite (3Al2O3·2SiO2), the raw materials, ie kaolinite, synthesized alumina, and different wt% of additives were wet mixed, dried, and uniaxially pressed followed by sintering at different temperature. 1600°C sintered samples from each batch exhibit enhanced properties. The 1 wt% TiO2 addition shows bulk density up to 2.96 g/cm3 with a maximum strength of 156.3 MPa. The addition of MgO up to 1 wt% favored the growth of mullite by obtaining a density and strength matching with the batch containing 1 wt% TiO2. These additives have shown a positive effect on mullite phase formation by reducing the temperature for complete mullitization by 100°C. Both additives promote sintering by liquid phase formation. However, the grain growth, compact microstructure, and larger elongated mullite crystals in MgO containing batch enhance its hardness properties.