Kinetic analysis of formation of magnesia spinel by thermal analysis

Thermal analysis of mixtures ofvarious alumina precursors (powders of fused corundum, smelter-grade alumina GKand non-smelter-grade alumina G-00, combustion product of xerogel from aluminumnitrate and citric acid) with periclase at different heating ratesis performed. By analyzing the shape and position of exothermicpeaks, which corresponded to the formation of magnesia spinel MgAl2O4, the values of the Avrami coefficient and theeffective values of the activation energy are determined according toKissinger, Augis-Bennett, and Ozawa equations. The effect of mechanoactivation (MA)of the reactants is analyzed. Co-treatment of periclase and corundum-containingreagents allowed reducing the activation energy of the reaction by15–20%. Pre-treatment of one of the components of the mixtureis most appropriate for periclase since it allowed reducingЕаby ~14%, whereas MA of corundum alone reduced thischaracteristic only by ~9%. Using the combustion product ofxerogel of alumina-oxide composition in spinel synthesis is very effectivesince it accelerated the process by reducingЕаby~11% even without MA. The values of the Avrami constantare found to be in the range 0.57–0.76, which correspondsto the mechanism of nucleation and crystal growth.