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

Abstract

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.

Effects of Particle Size on the Kinetics of Physico-geometrical Consecutive Reactions in Solid–Gas Systems: Thermal Decomposition of Potassium Hydrogen Carbonate

“…In this reaction stage, the particles were sticky and difficult to separate from one another, indicating the formation of gelatinated surface layers during IP. Similar gelation of reacting particles and contribution of the liquefied phase to the thermal decomposition process have been confirmed in thermal dehydration of several crystalline hydrates 64,65 and were expected in the thermal decomposition of NaHCO 3 . 32 The scale-like structure on the particle surfaces resulted from the solidification of the once liquefied surface layer, while cooling to room temperature.…”

Critical Appraisal of Kinetic Calculation Methods Applied to Overlapping Multistep Reactions

“…[1,2,3]. Thermal decomposition of solids represents a typical example of such complex process [4,5,6,7,8]. Determination of the kinetic parameters for the thermal decomposition is not a straightforward, but large experimental efforts should be paid for finding a possible way to attain the rigorous solution [9,10,11].…”

Physico-Geometrical Interpretation of the Kinetic Behavior of the Thermal Dehydration of β-Maltose Monohydrate

“…The thermal decomposition of solids exhibits complex kinetic behaviors that are constrained by the reaction geometry and solid–gas interactions. − This process is further complicated when a liquid phase contributes to the thermal decomposition process, which is the case for many thermal decompositions and dehydrations of solids in which various physical processes occur in the overall reaction, e.g., melting of reactant or product solids, − condensation of the evolved gas (water vapor) during the diffusional removal, − and deliquescence or gelation of the solid product induced by evolution of water vapor. − To understand the kinetic characteristics of processes involved, a simplification can be achieved by experimental separation of the chemical process of thermal decomposition or dehydration and the physical process of liquid phase formation, which is enabled by selecting the heating and atmospheric conditions when monitoring the thermal decomposition and dehydration processes. , On the other hand, the overlapping of thermal dehydration or decomposition and liquid phase formation provides the reaction process and the product with specific characteristics. , For example, the secondary reaction of the thermal dehydration product with the atmospheric CO 2 is promoted by the liquid water formed at the reaction interface of the thermal dehydration of crystalline hydrates and decomposition of hydroxides, which is of interest in terms of the greenhouse effect mitigation because it can be used for CO 2 capture from the environment. , Another specific characteristic of the process is the formation of glass and molten product, − among which the glassy products can find wide applications in many fields including food and pharmaceutical industries. The sophisticated control of the overlapping chemical and physical process is key to increase the functionalities of both reaction and product.…”

“…16−21 To understand the kinetic characteristics of processes involved, a simplification can be achieved by experimental separation of the chemical process of thermal decomposition or dehydration and the physical process of liquid phase formation, which is enabled by selecting the heating and atmospheric conditions when monitoring the thermal decomposition and dehydration processes. 8,21 On the other hand, the overlapping of thermal dehydration or decomposition and liquid phase formation provides the reaction process and the product with specific characteristics. 10,20 For example, the secondary reaction of the thermal dehydration product with the atmospheric CO 2 is promoted by the liquid water formed at the reaction interface of the thermal dehydration of crystalline hydrates and decomposition of hydroxides, which is of interest in terms of the greenhouse effect mitigation because it can be used for CO 2 capture from the environment.…”