Mechanism and Kinetics of Thermal Decomposition of MgCl₂ × 6H₂O

The reaction mechanism and kinetic behavior of thermal decomposition of MgCl₂ × 6H₂O were studied by thermal gravimetric analysis. The results showed that the thermal decomposition process of MgCl₂ × 6H₂O could be divided into six stages. In the first two stages, four crystalline waters were lost. The dehydration and hydrolysis coexisted during the third and fourth stages. The fifth stage corresponded to the evaporation of 0.3 crystalline waters, and one molecular hydrogen chloride was eliminated in the last stage. The kinetic analysis of the thermal decomposition process was performed using the Doyle, Coats–Redfern, and Malek methods. The results suggested that the mechanisms of six stages were two-dimensional phase boundary mechanism, three-dimensional phase boundary mechanism, nucleation and nuclei growth mechanism (Avrami–Erofeev equation n = 3), two-dimensional phase boundary mechanism, three-dimensional diffusion mechanism (cylinder and G-B equation), and nucleation and nuclei growth mechanism (Avrami–Erofeev equation n = 1), respectively. The apparent active energies of six stages were 66.8 kJ × mol⁻¹, 138.0 kJ × mol⁻¹, 77.2 kJ × mol⁻¹, 135.6 kJ × mol⁻¹, 77.4 kJ × mol⁻¹, and 92.2 kJ × mol⁻¹, respectively. The frequency factors were 3.6 × 10⁹ s⁻¹, 8.8 × 10¹⁷ s⁻¹, 4.6 × 10⁹ s⁻¹, 3.0 × 10¹⁴ s⁻¹, 78.6 s⁻¹, and 1.2 × 10³ s⁻¹, respectively.