Review of Oxygen Activities and Phase Boundaries in Wustite as Determined by Electromotive-Force and Gravimetric Methods

All data available in the literature regarding oxygen activities and composition limits for the wustite phase were analyzed critically. The most reliable activity data were collected into a composite in which (1) the partial molal free energy of oxygen varied linearly with composition and reciprocal temperature and (2) the partial molal enthalpy and entropy of oxygen varied linearly with composition and were independent of temperature. These linear variations of the thermodynamic properties are inconsistent with the presence of additional phases which have been reported within the wustite phase field. The composition limits of the wustite phase, which were computed from the composite, were in excellent agreement with Darken and Gurry's original phase diagram.