Phase Diagram Analyses

An equilibrium phase diagram represents the geometrical loci of thermodynamic parameters when equilibrium between different phases under a given set of conditions is established. Thus phase diagram and thermodynamic data of a system are interrelated. Many thermodynamic and physical properties are at least qualitatively inferred from the shapes of the phase diagrams. The thermodynamic functions such as heat of fusion, excess free energy of formation, activity and solubility can be calculated from the phase diagram. Analysis of phase diagram can further yield information regarding factors governing theories of alloying e.g. strain energy, size, valence, and electron concentration effects. The excess free energy of the liquid phase and the free energy of formation of a congruently melting compounds can be calculated from the liquidus data and the heats of fusion and formation of the compound. The methods of analyses depend on the shape of the liquidus in the vicinity of the compound. Brief accounts on such analyses suggested by Wagner and Jordan are included in this chapter.