Thermodynamic Phase Diagrams of Ternary Alloys Exposed to a Single Oxidant

Abstract

A simple example of an isothermal thermodynamic phase diagram for a quaternary system composed of a ternary A–B–C alloy reacting with a single oxidant (O) has been calculated assuming that oxides are insoluble and that they do not interact with each other. The 2D thermodynamic diagrams of the ternary metal–oxygen systems composed of the three types of binary alloys plus the oxidant are reviewed first, and then the 2D sections of the 3D phase diagram along planes of constant values of one of the variables involved are explored in detail. Finally, the structure of the 3D diagram is presented by means of appropriate figures and is discussed by examining in detail the connections between the critical curves, surfaces and volumes in 3D space with the corresponding critical features, including points, curves and surfaces, of the 2D sections. In addition, the possible application of thermodynamic diagrams to predict the nature of the oxidation products is briefly discussed in combination with the concept of oxidation maps.