Synthesis of magnesium aluminate spinel nanocrystallites by co-precipitation as function of pH and temperature

Abstract

Magnesium aluminate (MgAl2O4) spinel nanocrystallites are prepared through nitrate route with liquor ammonia as a precipitant by co-precipitation process. By varying the solution pH (8–10) and bath temperature (10–40°C), the precipitated gel materials are obtained. Yield of each batch is determined by firing at 1000°C with 2 hours (h) soaking. The yield is maximum at 30°C and pH 9.2. Chemical analysis indicates near stoichiometric spinel at pH 9.2. Below pH 9.2, Al2O3:MgO molar ratio shifts to alumina side; beyond pH 9.2, it is towards magnesia side. Stoichiometric spinel-forming precursor material is characterized by various techniques. X-ray diffraction (XRD) analysis indicates spinel formation at 600°C and its crystallinity increases with rise of temperature. Hydroxyl group and absorbed water in gel substrate disappear with variation of temperature as observed by Fourier transform infrared (FTIR). Only one exothermic response of the precursor of spinel formation is demonstrated through differential scanning calorimetry (DSC). Studies reveal formation of near stoichiometric magnesium aluminate spinel powder having average crystalline size in the range 15–38 nm. HR-transmission electron microscopy studies also confirm this nano-size crystallite formation.