Synthesis of manganese–zinc ferrite nanopowders prepared by a microwave-assisted auto-combustion method: Influence of sol–gel chemistry on microstructure

Based on the quantitative analysis and optimization of the complexing conditions for the sol–gel process, single phase Mn–Zn ferrite (Mn0.745Zn0.173Fe2.082O4) nanopowders with high saturation magnetization (MS=75.42emu/g) were one-step synthesized via a microwave-assisted sol–gel auto-combustion approach. The microstructures and magnetic property of the resulting powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy and magnetic measurement of M×H curves. The XRD patterns indicated that the low value of CA/M⁎ (the reduced molar ratio of citric acid to metal ions) and inadequate microwave irradiation are easy to result in the formation of impurity phases. Furthermore, the poor chelating of metal ions can be effectively improved by adding the ethylene glycol, which also acts as fuel to increase the reaction temperatures during the auto-combustions when oxidation degree Q (the relative amount of the oxidant) is high enough. The influences of the gel׳s chemistry, defined by the gel-parameters: CA/M⁎, oxidation degree Q and gross calorific value H (the total heat potentially produced by the complete oxidation of hydrocarbons), on the formation of single phase Mn–Zn ferrite nanopowders and their microstructures were investigated with the help of the orthogonal testing method. The microstructure of single phase Mn–Zn ferrite nanopowders is closely associated with the gel׳s chemistry. Moreover, the average grain size is more sensitively impacted by the gel-parameters than the residual microstrain and, relatively, the influences on the cell parameter are the smallest, with the impacting sequences of the gel-parameters: oxidation degree Q>gross calorific value H>CA/M⁎ for the grain size, oxidation degree Q>CA/M⁎>gross calorific value H for the microstrain and gross calorific value H>CA/M⁎ >oxidation degree Q for the crystal lattice parameter.