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.
*Lecture presented at the 9th IUPAC International
Symposium on Solubility Phenomena (9th ISSP), Hammamet, Tunisia, 25
28 July 2000. Other presentations are published
in this issue, pp. 761844.
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