Microstructure of Hydrated Magnesia and MgAl<sub>2</sub>O<sub>4</sub> Spinel Layer between Magnesia and Alumina

Abstract

Tests were performed to investigate the microstructure of MgAl2O4 spinel layer between magnesia and alumina after high temperature thermal treatment (1500 °C and 1600°C). The first test involved fused magnesia and alumina sol. Hydration of magnesia powders was studied in a controlled condition that soaked in aqueous solution at 80 °C for up to 1h and 2h. Microstructures of the samples were investigated by SEM, EDS, which showed that the formation of Mg (OH)2 made magnesia particles cracking, separated many punier particles. The punier particles combined with alumina sol, generated spinel at high temperature. A microstructurally distinct layer with granulate grains of up to 50μm width was observed after 3 h at 1600 °C. Spinel layer bordered alumina layer, and separated from magnesia layer. However, it was not found distinct spinel layer after 3 h at 1500 °C. The formation of small amount of spinel embedded in the layer of alumina, and penetrated the alumina layer. In the spinel 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.