Thermodynamics of ternary systems. Quasichemical approximation and the excess ternary term

Abstract

Based on the quasichemical theory, second order expressions in terms of the nearest-neighbor interaction parameters are given for the molar energy of mixing, ΔE, and the partial molar excess free energy of mixing, ḠCE, of a ternary system. In order to improve the applicability, the quasichemical binary contributions are replaced by the experimental binary values. The ``leftover'' term or the ``excess'' ternary term is discussed in more detail. The quasichemical theory suggests the ternary excess energy term is of a more complex form than N AN BNC × const. The expressions are useful in calorimetric work and in discussing phase stabilities (miscibility gaps).