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
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the BET model is no longer applicable.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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