Influence of the metal nitrates to citric acid molar ratio on the combustion process and phase constitution of barium hexaferrite particles prepared by sol–gel combustion method

A novel sol–gel combustion process was used to synthesize the ultrafine particles of barium hexaferrite. The nitrate–citrate gels were prepared from metal nitrates and citric acid solutions under various molar ratios of the metal nitrates to citric acid of 0.5, 1, 1.5 and 3 by sol–gel process. The results showed that the nitrate citrate gels exhibit a self-propagating behavior after ignition in air at room temperature. The thermal decomposition of nitrate–citrate gels and the phase evolution of calcined powder were investigated respectively by DTA/TG and XRD techniques. Scanning electron microscope was used to characterize the microstructure of the products. The results revealed that the formation temperature and the crystallite size of barium hexaferrite are influenced significantly by the molar ratio of the metal nitrates to citric acid. The formation temperature of barium hexaferrite decreases with increasing the molar ratio of the metal nitrates to citric acid.