Influence of nano boehmite on solid state reaction of alumina and magnesia

Effect of nano boehmite on formation of alumina–magnesia spinel via solid state reaction is reported. Various amounts of nano boehmite were added to Al2O3–MgO mixtures and the mixtures were heated at different temperatures ranging from 800 to1500 °C for 2 h. Phase structure and chemical composition of the samples were evaluated by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and differential thermal analysis (DTA) techniques. Scanning electron microscopy (SEM) was also employed to study microstructure of the fabricated samples. It was revealed that the formation temperature of MgAl2O4 spinel decreased significantly in the presence of nano boehmite. The initial spinel layer formed on magnesia particles was believed to play a mineralizing effect, and, therefore, accelerate the solid state reaction between magnesia and alumina. Nano boehmite also discouraged formation of hybonite (CA6) phase. The results are explained with emphasis on the importance of low temperature spinel formation in refractory materials.

Research highlights▶ In this research, we introduced nano boehmite as a novel additive in synthesis of magnesia–alumina spinel via solid state reactions. Using this additive, formation temperature decreases to below 700 °C which is comparable to that of the chemical routs and has not been already reported by other researchers for solid state methods. Moreover, it was revealed that addition of nano boehmite results in formation of a covering spinel layer on the magnesia and alumina particles. This layer suppresses formation of the calcium hexa aluminate phase at high temperatures.