Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe3O4) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe3O4 powders as characterized by X-ray diffractometry, infrared spectroscopy, N2 adsorption-desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe3O4 powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe2O3 and FeO together with Fe3O4 phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m2/g was transformed to disintegrated structure (76.5 m2/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.