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, ${Ḡ}_C^E$ , 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 _BN_C × const. The expressions are useful in calorimetric work and in discussing phase stabilities (miscibility gaps).