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Heterogeneous Kinetic Features of the Overlapping Thermal Dehydration and Melting of Thermal Energy Storage Material: Sodium Thiosulfate Pentahydrate C

Kameno, Nao, Koga, Nobuyoshi
Journal of physical chemistry 2018 v.122 no.15 pp. 8480-8490
anhydrides, liquids, melting, microscopy, reaction mechanisms, solids, thermal energy, thiosulfates
The thermal dehydration of sodium thiosulfate pentahydrate (STS-PH), which has been studied as a potential thermal energy storage material, was investigated from the points of view of the physicogeometric reaction mechanism, heterogeneous kinetics, and morphologies of the product. Thermoanalytical and microscopy techniques were used to demonstrate the physicogeometric events that control the apparent kinetics of the reaction under different reaction conditions. The thermal dehydration of STS-PH takes place via a two-step reaction that involves a dihydrate intermediate, and the contribution of the melting of STS-PH is a key characteristic. Reaction conditions alter the relative position of the melting of STS-PH with reference to the reaction stage of the thermal dehydration. Depending on the relative position of STS-PH melting, the reaction can occur in the solid state, solid–liquid state, or liquid state. A variety of physicogeometric events contribute to the reaction processes under different reaction conditions, generating different reactant/product configurations and reaction pathways controlled by specific physicogeometric reaction mechanisms. The anhydrides produced via different reaction pathways exhibit largely different morphologies that range from hollow particles to a spongelike agglomerate. It is expected that the findings presented herein contribute to the theoretical foundations of the complex heterogeneous kinetics in the solid state.