Low temperature pressureless sintering of sol-gel derived mullite

Mullite of stoichiometric composition has been synthesized by sol-gel process. Aluminium nitrate and ethyl silicate are used as the starting materials to prepare the single phase mullite powder. DTA shows that the mullitization starts at 971°C. It is observed from XRD analysis that the amorphous mullite completely transforms to orthorhombic crystalline mullite at 1300°C. Wet milling operation has enhanced the sintering density of pure mullite by 12% more than that of dry milling. The naturally available raw material, clay has been identified as one of the suitable sintering aids for mullite. The addition of clay to the mullite powder enhances the density up to 95% of TD even at a very low temperature, 1450°C by pressureless sintering. A viscous flow sintering mechanism during densification is one of the main criteria to achieve good densification.