The Zn-Fe-O system can be divided into three regions from the thermodynamic and metallurgical viewpoints: (i) Fe-Zn-ZnO-FeO system, (ii) FeO-ZnO-ZnFe2O4-Fe3O4 system and (iii) Fe3O4-ZnFe2O4-Fe2O3 system. Phase relations in each system have been studied at 1200 K by equilibrating synthetic samples in evacuated sealed quartz tubes. The results indicate that the phase relations at 1200 K are almost the same as that at 1100 K, while the mutual solid solubilities at 1200 K between ZnO and FeO are slightly larger than those at 1100 K. On the basis of the results and our previous EMF data using a stabilized zirconium oxide solid electrolyte, the equilibrium partial pressures of oxygen, -log pO(2) (= -log (PO(2)/Pθq)), at 1200 K were thus estimated as follows: 20-16 for region (i), 14-12 for region (ii) and 6-3 for region (iii), respectively. The activities of the components in Fe-Zn, FeO-ZnO and Fe3O4-ZnFe2O4 systems were then obtained by applying the Gibbs-Duhem relation in each region.
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