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Pure Appl. Chem. 74(10), 1909-1920, 2002

Pure and Applied Chemistry

Vol. 74, Issue 10

Solid�liquid equilibria in mixtures of molten salt hydrates for the design of heat storage materials*

W. Voigt and D. Zeng

TU Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg, Germany

Abstract: Enthalpy of melting can be used to store heat in a simple way for time periods of hours and days. Knowledge of the solid �liquid equilibria represents the most important presumption for systematic evaluations of the suitability of hydrated salt mixtures. In this paper, two approaches for predicting solid�liquid equilibria in ternary or higher component systems are discussed using the limited amount of thermodynamic data available for such systems. One method is based on the modified Brunauer�Emmett�Teller (BET) model as formulated by Ally and Braunstein.

In cases of a strong tendency toward complex formation of salt components, the BET model is no longer applicable. Reaction chain models have been used to treat such systems. Thereby, the reaction chain represents a method to correlate step-wise hydration or complexation enthalpies and entropies and, thus, reduce the number of adjustable parameters. Results are discussed for systems containing MgCl2, CaCl2, ZnCl2, and alkali metal chlorides.

* Lectures presented at the 10th International Symposium on Solubility Phenomena, Varna, Bulgaria, 22 -26 July 2002. Other lectures are published in this issue, pp. 1785-1920.


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