Effect of the citrate sol–gel synthesis on the formation of MgAl2O4 ultrafine powder

Nanocrystalline MgAl2O4 with average crystal sizes of about 100 nm were prepared by citrate sol–gel process at lower temperatures. The presence of small amounts of MgAl2O4 as crystal seed could obviously accelerate the crystallization of MgAl2O4. The effects of the amount and the size of crystal seeds on the formation of MgAl2O4 were investigated. The inceptive formation temperature of the MgAl2O4 not containing any crystal seeds was 600 °C, while the specimen containing 1 wt.% MgAl2O4 used as a crystal seed was 550 °C. The decrease in the inceptive formation temperature was due to MgAl2O4 serving as a substrate for heterogeneous nucleation which accelerated nucleation. The amount and the size of crystal seeds showed little influence on the formation of MgAl2O4 spinel. The prepared ultrafine MgAl2O4 spinel were characterized by X-ray diffraction (XRD), differential thermal analysis and thermogravimetric (TG–DTA) and scanning electron microscopy (SEM).