Formation mechanism of MnxFe3-xO4 by solid-state reaction of MnO2 and Fe2O3 in air atmosphere: Morphologies and properties evolution

Phase transformation of MnO2 and Fe2O3 roasted in air atmosphere at temperatures of 500-1400 degrees C for synthesizing manganese ferrite (MnxFe3 - O-x(4)) has been reported. In current work, the morphologies and properties of the MnxFe3 - xO4 products with various x values during the synthesis process were characterized by XRD, XPS, SEM-EDS, AFM, VSM and Vickers-type microhardness analyses to further understand the formation mechanism of MnxFe3 - xO4 from MnO2 and Fe2O3 by solid-state reaction. Results showed that the x value in the MnxFe3 - xO4 gradually increased to 1 with the extension of roasting time from 30 min to 120 min at 1300 degrees C. Morphology measurements indicated the MnxFe3 - xO4 particles presented polyhedron structure and the shape of polyhedron particles gradually became regular with the increasing of x value. In addition, it's interesting to find that the polyhedron particles had multi-layer stacking structure and the thickness of each layer was about 5 nm. The saturation magnetization of the MnxFe3 - xO4 samples increased with the rising of x value. A polyhedral MnFe2O4 (x = 1) product with saturation magnetization of 78.5 emu/g was obtained when the MnO2 and Fe2O3 briquettes with molar ratio of 1:1 were roasted at 1300 degrees C for 120 min. Moreover, the Hv hardness of the MnxFe3 - xO4 increased from 154.8 kg/mm(2) to 339.4 kg/mm(2) with elevating the temperature from 1000 degrees C to 1300 degrees C. (C) 2017 Elsevier B.V. All rights reserved.