Kinetic Analysis of Formation of Magnesia Spinel by Thermal Analysis

Thermal analysis of mixtures of various alumina precursors (powders of fused corundum, smelter-grade alumina GK and non-smelter-grade alumina G-00, combustion product of xerogel from aluminum nitrate and citric acid) with periclase at different heating rates is performed. By analyzing the shape and position of exothermic peaks, which corresponded to the formation of magnesia spinel MgAlO, the values of the Avrami coefficient and the effective values of the activation energy are determined according to Kissinger, Augis-Bennett, and Ozawa equations. The effect of mechanoactivation (MA) of the reactants is analyzed. Co-treatment of periclase and corundum-containing reagents allowed reducing the activation energy of the reaction by 15–20%. Pre-treatment of one of the components of the mixture is most appropriate for periclase since it allowed reducing E by ~14%, whereas MA of corundum alone reduced this characteristic only by ~9%. Using the combustion product of xerogel of alumina-oxide composition in spinel synthesis is very effective since it accelerated the process by reducing E by ~11% even without MA. The values of the Avrami constant are found to be in the range 0.57–0.76, which corresponds to the mechanism of nucleation and crystal growth.