The Synthesis And Characterization Of Binary Metal Composite Oxides Containing Iron And Manganese And Kinetics Of Thermal Process Of Precursors

Nano metal composite oxides have been the focus in the material chemistry fields because of their excellent magnetic and electrical performances. In this study, metal composite oxides CuFe2O4, MgFe2O4, BiFeO3and MnV2O6were synthesized by solid-state reaction at low heat. The precursors and their calcined products were characterized by XRD, TG/DSC, FT-IR, SEM, EDS, VSM. The crystal structure, morphology, magnetic performance and kinetics of thermal process were analyzed based on the results. This paper attempted to study the synthesis of binary metal composite oxides via a solid-state reaction at low heat and their magnetic performance, in order to provide helpful references for the development of soft magnetic materials.XRD results showed that the precursors of CuFe2O4, MgFe2O4, MnV2O6dried at about353K were well-crystallized. They were CuFe(C2O4)3-4.5H2O, MgFe(C2O4)3-6H2O and MnV2O6-4H2O, respectively. After calcining the precursors over773K, cubic CuFe2O4(space group F), the cubic MgFe2O4(space group Fd-3m(227)), and monoclinic MnV2O6 (space group C2/c(15)) could be obtained, respectively. Rhombohedral BiFeO3with space group R3c(161) could be obtained at873K. However, BiFeO3was unstable at high temperature. With temperature increasing, BiFeO3decomposed into Bi2Fe409. The SEM micrographs showed that the crystalline CuFe2O4, MgFe2O4, MnV2O6were composed of polyhedral grains. With the increase of calcining temperature, the calcined samples were aggregated into larger polyhedral grains further. The precursor of MnV2O6is rod-like morphology. When the temperature rised to1105K, the sample began to melt and the morphology became block shape. VSM results showed that the specific saturation magnetizations of CuFe2O4、 MgFe2O4、 BiFeO3were33.5、40.4、0.032emu·g-1, respectively. This indicates that CuFe2O4and MgFe2O4can be remarkably magnetized, while BiFeO3is difficult to be magnetized. MnV2O6did not reached saturation under the applied field. This indicates that the magnetic permeability of MnV2O6is low. The kinetics of the thermal decomposition of precursors was studied using TG-DSC technique. The results showed that the thermal process of CuFe(C2O4)3·4.5H2O or MgFe(C2O4)3·6H2O experienced three steps. Non-isothermal kinetics of the thermal decomposition was interpreted by KAS method and FWO method. The activation energies of the first step associated with the dehydration of crystal water molecules are85kJ-mol-1and149kJ·mol-1, respectively. The activation energies of the second step associated with the decomposition of oxalate and the oxidation of Fe2+into Fe3+are107kJ·mol-1and184kJ·mol-1, respectively, and the corresponding functions are both g(a)=1-(1-α)1/4. The third step corresponds to the phase transition from amorphous solids to crystalline solids. Based on the Kissinger equation, the values of the activation energies associated with the thermal decomposition of MnV2O6·4H2O are determined to be55.27kJ·mol-1and98.30kJ·mol-1for the first and second dehydration steps, respectively. The melting point of MnV2O6is at about1105K. Based on the Kissinger equation, the activation energy of thermal decomposition of precursor of BiFeO3is132.11kJ·mol-1. Based on the JMA equation, the activation energy of crystallization process of BiFeO3is324.40kJ·mol-1.