Thermodynamic study on the zinc-iron-oxygen system at 1200 K

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 p_O(2) (= -log (P_O(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.