Products and non-isothermal kinetics of thermal decomposition of MgFe2(C2O4)3·6H2O

Abstract

MgFe2(C2O4)3·6H2O was synthesized by solid-state reaction at low heat using MgSO4·7H2O, FeSO4·7H2O, and Na2C2O4 as raw materials. The spinel MgFe2O4 was obtained via calcining MgFe2(C2O4)3·6H2O above 500 °C in air. The MgFe2(C2O4)3·6H2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform FT-IR, X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The result showed that MgFe2O4 obtained at 800 °C had a specific saturation magnetization of 40.4 emu g−1. The thermal process of MgFe2(C2O4)3·6H2O experienced three steps, which involves the dehydration of the six waters of crystallization at first, and then decomposition of MgFe2(C2O4)3 into amorphous MgFe2O4 in air, and at last crystallization of MgFe2O4. Based on Flynn–Wall–Ozawa equation, the average values of the activation energies associated with the thermal decomposition of MgFe2(C2O4)3·6H2O were determined to be 148.45 ± 25.50 and 184.08 ± 7.64 kJ mol−1 for the first and second decomposition steps, respectively. Dehydration of the six waters of MgFe2(C2O4)3·6H2O is multi-step reaction mechanisms. Decomposition of MgFe2(C2O4)3 into MgFe2O4 could be simple reaction mechanisms, kinetic model that can better describe the thermal decomposition of MgFe2(C2O4)3 is the F3/4 model, and the corresponding function is g(α) = 1 − (1 − α)1/4.