Enhancement of reaction-sintering of alumina-excess magnesium aluminate spinel in presence of titania

Alumina-excess magnesium aluminate spinel finds use in different high temperature applications including steel ladles. Alumina-excess spinel was prepared by solid oxide reaction using magnesia (MgO=10 wt%) and calcined alumina (Al2O3 = 90 wt%), in the sintering temperature range of 1500-1700 °C. The role of titania on the densification, spinelisation, evolution of microstructure and phase assemblage was investigated in this MgO-Al2O3 system. Titania addition increased the rate of densification 20x compared to undoped composition at 1500 °C under dynamic heating condition. However, under static firing, the beneficial effect of titania on densification could only be discerned at lower temperatures. The microstructure of titania doped sintered alumina-excess spinel compacts contain magnesium aluminium titanate phase in the grain boundary of corundum and spinel grains. The beneficial effect of titania on densification is attributed to magnesium aluminium titanate phase (MgxAl2(1-x)Ti(1+x)O5) development and also by incorporation of Ti4+ into the spinel structure.