Determination of kinetic characteristics of polycrystalline ferrites oxidation using TG analisis

Using non-isothermal thermogravimetry (TG), the oxidation kinetics of oxygen-deficient lithium-titanium ferrospinel, Li_0.649 Fe_1.598 Ti_0..5Zn_0..2Mn_0.051O_4-δ, manufactured by ceramic engineering is investigated. The oxidation annealing of powder samples is performed in air. According to the X-ray phase analysis, the processes giving rise to variations in oxygen content occur within single-phase spinel structure. The experimental kinetic results are processed using the Netzsch Thermokinetics software. The oxidation rate constants and the effective coefficients of atmospheric oxygen diffusion into the ferrites are determined. The effective activation energy E of oxygen diffusion is found to be 1.95 eV. It is demonstrated that an increase in the oxygen non-stoichiometry parameter δ as a result of recovery annealing of ferrite powders in vacuum at T=1070 K for 2 hours gives rise to a slight decrease in E down to 1.89 eV. The activation energy of oxygen grain-boundary diffusion is identified by the electroconduction method. The resulting value 1.93 eV is fairly consistent with that obtained by TG.