Thermal Dehydration of Lithium Sulfate Monohydrate Revisited with Universal Kinetic Description over Different Temperatures and Atmospheric Water Vapor Pressures

This study aims to universally describe the kinetic features of the thermal dehydration of lithium sulfate monohydrate across different temperatures (T) and atmospheric water vapor pressures (p(H2O)) as a model reaction of the thermal dehydration of crystalline hydrates. The features of the physicogeometrical consecutive process, comprising the induction period (IP)–surface reaction (SR)–phase boundary-controlled reaction (PBR), and the effect of p(H2O) on kinetic behavior were revealed experimentally under various heating conditions. Then, the accommodation function (AF), accounting for the effect of p(H2O) on the kinetic behavior, was derived by considering the consecutive/concurrent elementary steps of SR and PBR at the atomic and molecular levels. The universal kinetic descriptions for the IP and subsequent mass-loss process were realized by introducing the AF into formal kinetic equations and using the isoconversional kinetic relationship. Furthermore, by combining the physicogeometrical consecutive IP–SR–PBR(n) model and the formulated AF, the universal kinetic descriptions for each physicogeometrical reaction step across different T and p(H2O) conditions were obtained, which reveal novel kinetic features of each reaction step and these variations as the reaction step advances. The significance of the revealed kinetic features is discussed through demonstrating the development of the novel kinetic approach.