Magnetic Nanocrystalline Mg_(0.5)Zn_(0.5)Fe_2O_4: Preparation, Morphology Evolution, and Kinetics of Thermal Decomposition of Precursor

摘要

Mg_(0.5)Zn_(0.5)Fe_2(C_2O_4)_3·H_2O was synthesized by solid-state reaction at low heating temperatures using MgSO_4·7H_2O, ZnSO_4·7H_2O, FeSO_4·7H_2O, and Na_2C_2O_4 as raw materials. The spinel Mg_(0.5)Zn_(0.5)Fe_2O_4 was obtained via calcining Mg_(0.5)Zn_(0.5)Fe_2(C_2O_4)_3·H_2O above 400℃ for 1 h in air. The Mg_(0.5)Zn_(0.5)Fe_2(C_2O_4)_3·H_2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The results showed that Mg_(0.5)Zn_(0.5)Fe_2O_4 obtained at 400℃ had a specific saturation magnetization of 27.3 emu g~(-1). The thermal process of Mg_(0.5)Zn_(0.5)Fe_2(C_2O_4)_3·H_2O experienced three steps, which are: first, the dehydration of water of crystallization and decomposition of Mg_(0.5)Zn_(0.5)C_2O_4 into MgO and ZnO, then the reaction of Fe_2(C_2O_4)_3 with MgO and ZnO into amorphous Mg_(0.5)Zn_(0.5)Fe_2O_4, and at last the crystallization of Mg_(0.5)Zn_(0.5)Fe_2O_4. Based on the KAS equation and the OFW equation, the values of the activation energies associated with the thermal process of Mg_(0.5)Zn_(0.5)Fe_2(C_2O_4)_3·H_2O were determined to be 69 ± 11 and 71 ± 9 kJ mol~(-1) for the first and second thermal process steps, respectively.