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Pure Appl. Chem., 2001, Vol. 73, No. 5, pp. 807-823

Solid-state solubility and its limits. The alkali halide case

H. A. J. Oonk

Chemical Thermodynamics Group, Debye Institute, Faculty of Chemistry, Petrology Group, Geodynamics Research Institute, Faculty of Earth Sciences, Utrecht University, Padualaan 8, NL-3584 CH Utrecht, The Netherlands

Abstract: The group of binary common-ion alkali halide systems correspond to an excellent vehicle for discussing and demonstrating the influence of mismatch in sizebetween the building units of the host crystal and the units of the gueston the formation of mixed crystals and the limits of solid-state solubility. The numerical values of just four constants are needed to formulate a uniform thermodynamic description of the mixed crystalline state of the group of systems. In terms of deviation from ideal mixing behavior, in terms of the excess Gibbs energy, two constants are needed to relate the magnitude of the function to mismatch in size. One constant is to account for the asymmetry of the function, and one to express the dependence on temperature. The values of the constants have been assessed with the help of data available for 13 systems showing complete miscibility. The uniform description allows one to calculate, for every system of the group, the solubilities of the components in one another at any temperature.