ABSTRACT
The thermodynamic work of Josiah Willard Gibbs, carried out in the USA in the latter part of the 19th century, provided the fundamental foundation for the understanding of phase equilibria and for the representation of such equilibria in the form of equilibrium (phase) diagrams. The development of the field of phase diagrams has been accompanied by the publication of a number of important textbooks, which overall provide wide coverage of topics, including the interpretation of ternary and higher order systems. To represent completely the phase equilibria at constant pressure in a ternary system, a three dimensional model, commonly termed a space model, is required; the representation of composition requires two dimensions, and that of temperature, a third dimension. An invariant equilibrium exists only at a particular temperature in ternary systems, and the compositions of each of the four phases lie at fixed points on a plane in the space model corresponding to the particular temperature.
