Tailoring the microstructure of mechanoactivated Al2O3 and SiO2 mixtures with TiO2 addition

This paper reports on the effect of TiO2 on mullitization, anisotropic grain growth and densification of Al2O3 and SiO2 mixtures, which are activated by a high-energy ball milling process using tungsten as milling media. High-energy activation significantly promotes mullitization in the mixture of Al2O3 and SiO2 powders, and is a pre-requisite for the occurrence of anisotropic grain growth of mullite. There is a subtle interplay and competition between anisotropic grain growth and densification, depending on the amount of TiO2. Small amount of TiO2 has a positive effect on the phase formation and anisotropic grain growth of mullite, while high concentration of TiO2 suppresses anisotropic grain growth, and thus is beneficial to densification. As a result, the microstructure and densification of the mullite ceramics can be manipulated by the doping levels of TiO2.