Thermal decomposition and non-isothermal kinetics of microcrystalline magnesite

The thermal decomposition (TD) of magnesite is crucial for its high-value applications, and understanding its reaction mechanisms requires establishing accurate kinetic models. This research investigates the TD kinetics of microcrystalline magnesite under varying heating rates (HRs) using thermogravimetry and differential scanning calorimetry (TG–DSC) analysis. Kinetic parameters were derived using the Coats–Redfern (CR), Kissinger–Akahira–Sunose (KAS), and Flynn–Wall–Ozawa (FWO) methods. The influence of HRs on the decomposition process and the resulting MgO morphology was analyzed. The results demonstrated that as HRs increased, the decomposition and reaction rate curves shifted to higher temperatures, necessitating elevated temperatures for similar levels of decomposition. The mean activation energy ($E_a$) was calculated to be 162.45 kJ/mol, with a strong linear correlation between the $E_a$ and pre-exponential factor, suggesting robust kinetic compensation. The TD followed a two-dimensional phase boundary mechanism with cylindrical symmetry. “Original shape pseudomorphs” were found to significantly affect the microstructure, particle size variation, and kinetic behavior of the decomposition products. These findings provide important insights for the industrial processing of microcrystalline magnesite.