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the BET model is no longer applicable.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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