Potential-pH Diagrams for Iron in Supercritical Water

Potential-pH diagrams for the iron-water system were extended into the supercritical temperature range using thermodynamic data generated by the quasi-thermodynamic model of Helgeson, et al. For subcritical temperatures (T < 374°C), the diagrams agreed well with those available in the literature. The domain of thermodynamic immunity of iron decreased significantly with increasing T, particularly > 300°C. The domain of possible protection of iron by formation of a thermodynamically stable passive oxide layer shifted to lower pH values with increasing T.