General phase diagram sections

摘要

In the last 25 years there has been a rapid development of software for the calculation of chemical equilibria and of large databases of evaluated thermodynamic data for pure substances and solutions. It is now possible to calculate, with good precision, the conditions of T, P, compsoition and chemical potentials for complex multiphase equilibria involving large numbers of components. Such calculations are being applied to a wide variey of high temperature systems and processes. For a given T, P and overall compsoition, minimization of the Gibbs energy gives the equilibrium phase compositions. However, such as calculation for a single set of conditions is of limited use in large systems. What one really wants to know is what will happen as conditions are varied. Large tabular outputs are very hard to interpret. We need to plot phase equilibrium diagrams in which two variables are chosen as axes while others are held constant. In the general case, the variables of interest are T, P, various composition ratios, and chemical potentials (such as Po_2, Pso_2, etc.). Some of the possible diagrams are already familiar as T-composition or P-compsoition diagrams, isopleths of multicomponent systems, "predominance diagrams" of many types, and so on. However, there are also many less familiar but very useful types of phase diagram sections.