Microstructure of Hydrated Magnesia and MgAl2O4 Spinel Layer between Magnesia and Alumina

Tests were performed to investigate the microstructure of MgAl2O4 spinel layer between magnesia and alumina after high temperature thermal treatment (1500 degrees C and 1600 degrees C). Hydration of magnesia powders was studied in a controlled condition that soaked in aqueous solution at 80 degrees C for up to 1 h and 2 h. Microstructures were investigated by SEM, EDS. The formation of Mg(OH) 2 resulted in magnesia particles cracking, and generated many punier particles. At high temperature, the punier particles reacted with alumina sol to produce spinel. A microstructurally distinct layer with granulate grains of up to 50 mu m width was observed after 3 h at 1600 degrees C. Spinel layer bordered alumina layer, and separated from magnesia layer. Spinel phase close to alumina layer contained 8.79% Mg by atomic, while spinel phase away from alumina layer contained 13.07% Mg by atomic. However, it was not found distinct spinel layer after 3 h at 1500 degrees C. The formation of small amount of spinel embedded in the layer of alumina, and penetrated the alumina layer.