ABSTRACT
This chapter discusses ternary phase diagrams can be constructed from any combination of any of the multitude of types of binary diagrams. It also discusses the suitability of any material is governed by the factors. The phase rule is of great use in phase change material heat storage research, relating an array of properties for systems at equilibrium. Systems with a sufficient degree of nonideal behavior may be “partially isomorphous”, forming solid solutions over only a portion of the total composition range. The lever rule is equally valid if the phase diagram is plotted in weight percent and the liquid to solid ratio calculated as a weight relation. Congruent-melting intermediate phase compositions are desirable for heat storage, since they melt cleanly and reversibly at a single temperature. When the two components lack complete mutual solubility, a miscibility gap can occur over part of the composition range.
