Electrochemical Measurements of Elevated‐Temperature Thermodynamic Properties of Certain Iron and Manganese Oxide Mixtures

Measurements have been made in the temperature range 750° to 1050°C. of the temperature dependence of the electromotive force of the solid‐electrolyte galvanic cells image and from these data the variation with temperature of the relative partial molar free energy of oxygen on the right side of the foregoing cells was calculated. In the case of the first of these cells, a favorable comparison was made between the present values of this thermodynamic quantity and those predicted from published thermodynamic data for this oxide mixture. The lack of gas equilibria data for the manganese oxide mixture prevented such a comparison in the second instance, however, and there were substantial discrepancies between the present values of the relative partial molar free energy of oxygen and those obtained from published calorimetric data. This disparity in results was rationalized on the basis of possible differences in the metal‐oxygen ratio for the manganese oxide specimens measured by the two different techniques.