Sintering and microstructural study of mullite prepared from kaolinite and reactive alumina: Effect of MgO and TiO ₂

Abstract Mullite ceramic was prepared using kaolinite and synthesized alumina (combustion route) by solid‐state interaction process. The influence of TiO ₂ and MgO additives in phase formation, microstructural evolution, densification, and mechanical strengthening was evaluated in this work. TiO ₂ and MgO were used as sintering additives. According to the stoichiometric composition of mullite (3Al ₂ O ₃ ·2SiO ₂ ), 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% TiO ₂ addition shows bulk density up to 2.96 g/cm ³ 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% TiO ₂ . 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.