The effect of the concentration of citric acid and pH values on the preparation of MgAl2O4 ultrafine powder by citrate sol–gel process

Ultrafine MgAl2O4 was synthesized by citrate sol–gel process. A model was presented to evaluate the concentration of species in a citric solution for preparing MgAl2O4 ultrafine powder. The evaluated concentration of species can provide valuable information and help in selecting the optimal condition for preparation of MgAl2O4 powder by citrate sol–gel process. The influence of molar ratio of cations, citric acid and pH on the formation of MgAl2O4 was studied. The spinel precursor gel and the ultrafine MgAl2O4 spinel were characterized by X-ray diffraction (XRD), differential thermal analysis, thermogravimetric (TG-DTA) and scanning electron microscope (SEM). The results show that the MgAl2O4 spinel phase begins to form at 600 °C, and most of MgAl2O4 crystals are spherical with a crystal size about 30–50 nm.