Representation of mixed reactive gases on free energy (Ellingharn-Richardson) diagrams

TLDR: In this article, a modification of conventional free energy diagrams that includes a means of portraying the equilibria between H, H2, O2, and H2O is developed, based on the oxidation reaction of H/H2 mixtures at any fraction H, and the equilibrium is portrayed on the free energy diagram by means of a two-dimensional nomographic scale.

Abstract: Free energyvs temperature (Ellingham-Richardson) diagrams provide a convenient and useful means of portraying equilibria for a variety of systems, such as oxides, sulfides, and carbides. The oxide diagrams typically include nomographic scales that facilitate determination of the oxygen partial pressure, the H2/H2O ratio, and the CO/CO2 ratio in equilibrium with the oxides at any temperature. In addition, monatomic hydrogen provides a potentially useful means for the reduction of oxides in metal processing schemes but, at present, can only be produced in H2 at fractions less than unity. In the present work, a modification of conventional free energy diagrams that includes a means of portraying the equilibria between H, H2, O2, and H2O is developed. The modification is based on the oxidation reaction of H/H2 mixtures at any fraction H, and the equilibria are portrayed on the free energy diagram by means of a two-dimensional nomographic scale. The diagram illustrates the potential utility of H and H/H2 mixtures for oxide reduction and can be used in essentially the same manner as conventional free energy diagrams. The modification can conceivably be extended to other gaseous systems or diagram types, such as those for sulfides.