Effect of Fuel Choice on the Aqueous Combustion Synthesis of Lanthanum Ferrite and Lanthanum Manganite

High-surface area, nanocrystalline powders of two closely related peroviskite oxides, LaFeO3 and LaMnO3, were produced by aqueous combustion synthesis using two different fuels. LaMnO3 powders synthesized using glycine fuel had a higher surface area and a smaller crystallite size than when synthesized using ethylene glycol fuel. However, the opposite was observed for LaFeO3 powders, where a higher surface area and a smaller crystallite size was obtained using ethylene glycol. The effect of the fuel type on the powder properties was attributed to the combustion characteristics, such as the rate of temperature increase and maximum measured temperature, and the mode of combustion synthesis. The lower surface area LaFeO3 and LaMnO3 powders had higher rates of temperature increase, which is characteristic of a volume combustion synthesis mode. The high-surface area LaFeO3 powder produced using ethylene glycol fuel, in contrast, had a lower rate of temperature increase, representative of a self-propagating high-temperature synthesis mode. Differential thermal analysis showed that the mode of combustion correlated to the delayed reaction of the iron nitrate oxidizer with the ethylene glycol fuel. For the combustion synthesis of multication complex oxides, each fuel–oxidizer reaction is important for predicting the combustion characteristics and the resulting powder properties.