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

Ultrafine MgAl{sub 2}O{sub 4} was synthesized by citrate sol-gel process. A model was presented to evaluate the concentration of species in a citric solution for preparing MgAl{sub 2}O{sub 4} ultrafine powder. The evaluated concentration of species can provide valuable information and help in selecting the optimal condition for preparation of MgAl{sub 2}O{sub 4} powder by citrate sol-gel process. The influence of molar ratio of cations, citric acid and pH on the formation of MgAl{sub 2}O{sub 4} was studied. The spinel precursor gel and the ultrafine MgAl{sub 2}O{sub 4} spinel were characterized by X-ray diffraction (XRD), differential thermal analysis, thermogravimetric (TG-DTA) and scanning electron microscope (SEM). The results show that the MgAl{sub 2}O{sub 4} spinel phase begins to form at 600 deg. C, and most of MgAl{sub 2}O{sub 4} crystals are spherical with a crystal size about 30-50 nm.