Thermal decomposition mechanism of MgSO4·7H2O

Abstract

Sulfates exhibit high melting and decomposition temperatures, making them promising candidates for application in third-generation concentrated solar power systems. Sulfates in salt lakes typically crystallize as MgSO₄·7H₂O. This study investigates the thermal decomposition mechanism of MgSO₄·7H₂O through a combination of thermodynamic calculations and experimental characterization techniques, including thermogravimetry-differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), and thermogravimetry-Fourier transform infrared spectroscopy (TG/FTIR). The results reveal that the dehydration of MgSO₄·7H₂O proceeds through intermediate phases, yielding MgSO₄·6H₂O, MgSO₄·H₂O, and ultimately MgSO₄, without the formation of hydrolysis products. Phase-pure MgSO₄ can be effectively prepared through heating MgSO₄·7H₂O within the temperature range of 300 °C–850 °C. The decomposition of MgSO₄ produces MgO along with gaseous SO₃, SO₂, and O₂. The decomposition of MgSO₄ in atmospheric environment was found to be a gradual process, with initial and complete decomposition temperatures of 875.21 °C and 1044.3 °C, respectively. This study provides a thermodynamic basis for comprehending the thermal decomposition behavior of MgSO₄·7H₂O, and offers fundamental data for the application of MgSO₄·7H₂O and MgSO₄ as energy storage materials.