Kinetic Analysis of Magnesia Spinel Formation by Thermal Analysis

Abstract

Thermal analysis of mixtures of various alumina precursors (powders of fused corundum, metallurgical alumina and non-metallurgical G-00, a product of combustion of xerogel from aluminum nitrate and citric acid) with periclase, at different heating rates, was performed. By analyzing the shape and position of exothermic peaks that corresponded to magnesia spinel MgAl₂O₄ formation, the effective values of the activation energy were determined according to the Kissinger, Augis–Bennett, and Ozawa equations, as well as the values of the Avrami coefficient. The effect of mechanical activation (MA) of reagents was analyzed. The joint treatment of periclase and corundum-containing reagents made it possible to reduce the activation energy (E_a) of the reaction by 15–20%. The pretreatment of one of the mixture components was the most appropriate for periclase, since it allowed to reduce E_a by ~14%, while the MA of corundum alone reduced this characteristic by only ~9%. The use of xerogel combustion product of aluminum oxide composition in the synthesis of spinel was very effective, as it accelerated the process by reducing E_a by ~11% even without MA. The values of the Avrami constant were in the range of 0.57–0.76, which corresponded to the mechanism of nucleation and crystal growth.