Phase Diagrams for an Associated Solution

摘要

The model of an ideal associated solution is widely used in current practice for calculating the thermody-namic characteristics of liquid multicomponent systems [1-3]. Over the course of many years, we developed a version of the associated-solution model allowing us to take into account the existence of associates of various compositions, sizes, and shapes [4-7]. It was shown that the model parameters could be estimated from the melting points of individual substances by calculating the energy of an associate in the pair nearest neighbor approximation under the assumption that the infinite associate was a crystal. In addition, such an approach enables us to calculate not only the thermody-namic mixing characteristics, but also the phase diagrams for solutions. It turned out that a quite realistic hierarchy of phase diagrams can be obtained for systems that are mutually soluble only in the liquid phase and are not soluble in the solid phase. This pertains to eutectic systems and to systems that form a stable solid compound. We established the determining role of associates composed of identical atoms (self-associates) for the properties of simple eutectics. Further development of the model enabled us to include into investigation associates with arbitrary stoichiometry [8]. In this case, the problem is solved with a single fitting parameter such as the exchange energy for a regular solution [9]. Inclusion of associates arbitrary stoichiometry into investigation makes it possible to describe various concentration dependences of the ther-modynamic mixing characteristics for liquid alloys and to expand the range of systems to which this model is applicable. This primarily pertains to alloys with unlimited solubility near the melting point in the solid and liquid phases.