Effect of polymorphism of Al2O3 on the synthesis of magnesium aluminate spinel

MgAl2O4 spinel was prepared by reaction sintering and the effect of polymorphism of Al2O3 on the synthesis and densification of the spinel studied. γ-Al2O3, ρ-Al2O3 and α-Al2O3 were mixed with analytical reagent of MgO according to the stoichiometric spinel ratio, respectively, and pressed into billets with diameter of 20 mm and height of 15 mm. The green-body billets then were sintered at temperature from 800 °C to 1600 °C in an air atmosphere. Bulk density, porosity, linear expansion changes, phase composition, microstructure and grain size of final sintered products were analyzed. The results indicated that γ-Al2O3 is beneficial for synthesize of spinel because it has a crystal structure similar to that of spinel. Among materials sintered at 1600 °C for 3 h, samples using γ-Al2O3 as raw material had the highest density, up to 91% of the theoretical density of MgAl2O4, and had the largest grain size of spinel.