Microwave-assisted combustion synthesis of nanocrystalline MgAl2O4 spinel powder

A stoichiometric MgAl2O4 spinel powder was synthesized by a microwave-assisted combustion synthesis (MWCS) route. For the purpose of comparison, another stoichiometric MgAl2O4 spinel powder was also prepared following the conventional combustion synthesis (CCS) method. The batch size had a strong influence on the specific surface area of the material, which in turn is highly dependent on the preparation method adopted. The surface areas of these synthesized powders were found to decrease from 36.78 to 0.1 m2/g for MWCS and 126 to 8.06 m2/g for CCS samples, respectively, when the batch size was increased from 2 to 100 g. This could be attributed to sintering of the samples due to high adiabatic temperature generated as a result of increased heat accumulation with bigger batch quantities. Between the two powders synthesized by the two different routes, the powders obtained by MWCS and CCS routes were found to contain grains/crystals in range of 20-50 and 100-250 nm size, respectively. The thermogravimetry/differential thermal analysis (TG-DTA) and X-ray diffraction (XRD) studies reveal that microwave-assisted combustion synthesis route yields materials with higher degree of compositional stability and phase purity as compared to the conventional combustion synthesis method.