A study on non-isothermal kinetics of the thermal decompositions of β-manganese dioxide

In this research, the thermal decompositions of β-manganese dioxide (β-MnO2) under different atmospheres of dynamic nitrogen and air were investigated by TG, DTG, DSC and XRD techniques. Non-isothermal studies clearly indicate that two decomposition stages occur over the temperature regions of 30–1100 °C: the decomposition of β-MnO2 to Mn2O3 and of this oxide to Mn3O4 in both nitrogen and air. β-MnO2 decomposes at higher temperatures in air. The model-free kinetic analysis method together with the minimum deviation approach was employed to determine the activation energy (Ea) and the kinetic model function (mechanism) of the thermal decomposition process from a series of thermogravimetric experiments. The results show that β-MnO2 exhibits higher values of the activation energy (Ea) and the pre-exponential factor (A) in air. Compared with various solid state reaction models, the reactions are best described by the random nucleation and nuclei growth models.