Phase equilibria in multicomponent systems

The phase equilibrium in a multicomponent system is altered when one of the phases is finely divided, i.e. has a sharp curvature. In this section the effects of curvature on vapor pressures and solubilities will be discussed. 

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The basic problem in determining phase equilibria in multicomponent systems is the existence of a large number of variables, necessitating extensive experimental work. If ten measurements are considered satisfactory for acceptable characterization of the solubility in a two-component system in a particular temperature range, then the attainment of the same reliability with a three-component system requires as many as one hundred measurements. Therefore, a reliable correlation method permitting a decrease in the number of measurements would be extremely useful. Two different methods - the first of them based on geometrical considerations, and the second on thermodynamic condition of phase equilibria - are presented and their use is demonstrated on worked examples. 

The adjustable interaction constants Q can be evaluated from the experimental data for three-component systems these constants can then be employed for concentration of temperature interpolations and also for calculation of phase equilibria in multicomponent systems. Moreover, the constants Q usually depend very little on temperature, as the relative molalities, related to the solubility of the substance in the pure solvent, are employed hence calculations of other isotherms can be carried out easily. 

Palatink, L. S. and Landau, A. I. 1964, "Phase Equilibria in Multicomponent Systems" (New York Holt, Rinehart and Winston). Levin, E. M., Robbins, C. R. and McMurdie, H. F. 1964, "Phase Diagrams for Ceramists" (Columbus The American Ceramic Society). Levin, E. M., Robbins, C. R. and McMurdie, H. F. 1969, "Phase Diagrams for Ceramists, 1969 Supplement" (Columbus The American Ceramic Society). 

G. Della Gatta and G. Varone, Proc. Second. CODATA Symposium on Critical Evaluation and Prediction of Phase Equilibria in Multicomponent Systems, Paris, 1985, p. 576. 

In Chapter 1 it was shown that the equality of chemical potential and the common-tangent construction were equivalent ways of describing phase equilibria in multicomponent systems. However, when one or more of... 

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