PICTORIAL REPRESENTATION OF SOLID-GAS EQUILIBRIA AT HIGH-TEMPERATURES

A pictorial representation of solid-gas equilibria is useful for studying the thermodynamics of a system under consideration. These diagrams show the stability regions of the species involved in a system as functions of pressures of two reacting gases. A computer program initially developed to plot the predominance area diagrams for metal-sulfur-oxygen (M-S-O) systems in roasting processes has been modified and generalized to handle any solid-gas system. This program has been utilized to plot the predominance area diagrams (PAD) for metal-sulfur-oxygen and metal-oxygen systems. The only data input required by the computer are the standard free energy values of all species existing in a system. Using these diagrams, the optimum pressures of the reacting gases can be determined easily to form the desired species that are stable under these pressure conditions. The computer program may prove to be an important tool for studying thermodynamics of solid-gas systems in different processes like sulfidization roasting, chloridization roasting, volatilization roasting, direct reduction processes in sponge iron manufacturing, high-temperature oxidation, chemical vapor deposition, and reaction sintering of ceramics.