Analysis of thermodynamic parameters of crystallization of eutectic composition in the H2O - Na2S2O3∙5H2O system

Abstract

In the development of cold accumulators based on phase transitions (CA PT), the main efforts are currently aimed at calculating various structural devices and parameters such as volume, surface area of the CA, heat transfer coefficient (or thermal resistance) at the boundary of the cold storage material (CSM) with the battery material, charging and discharge temperature and time, energy efficiency. At the same time, the physical and chemical problems of accounting for the processes of phase transitions themselves and their impact on the effective operation of CA are poorly covered. In this work, the analysis of kinetic and thermodynamic parameters of melting and crystallization of eutectic composition in the H₂O- Na₂S₂O₃∙5H₂O system (TSN-5) was carried out using experimentally obtained thermograms. Depending on the amount of heating of the liquid phase with respect to the melting temperature and further cooling, there are two types of crystallization. The first kind is quasi-equilibrium crystallization (QEC), which occurs at a temperature coinciding with that of T_L = T_E. The second species is non-equilibrium-explosive crystallization (NEC), which begins after certain pre-crystallization  hypothermia have been achieved. Activities , , activity coefficients , , and activation energy ,  were calculated in eutectics, both at T_E, i.e., equilibrium crystallization (QEC), and in the supercooling region at Tmin at the onset of non-equilibrium-explosive crystallization (NEC).