Phase relations in the FeO-ZnO-ZnFe2O4-Fe3O4 system at 1, 100 K have been determined by the X-ray microanalysis and X-ray diffraction studies of the quenched samples. The results indicate that magnetite (Fe3O4) and zinc ferrite (ZnFe2O4) form a complete series of solid solutions in the Fe3O4-ZnFe2O4 system, while there is a miscibility gap in the FeO-ZnO system. Lattice constants for the Ze3O4-ZnFe2O4 spinel solid solutions in equilibrium with the Fe0-ZnO system exhibit positive deviations from Vegard's law.
The partial oxygen pressures were measured by an e.m.f. method using the stabilized zirconia solid electrolytes, the activities were obtained by applying the Gibbs-Duhem relations to the oxide phases. Activity of zinc oxide in the FeO-ZnO system coexisting with the Fe3O4-ZnFe2O4 solid solutions at 1, 100 K shows a considerable positive deviation from Raoult's law except that at ZnO-rich side it exhibits a slight positive deviation from Raoult's law in the range up to the solid solubility limit. The activity coefficients at infinite dilution, reFeo and γ0znO, at1, 100K were estimated at 4.7 and 0.9, respectively.Both the activities of magnetite and zinc ferrite in the Fe3O4-ZnFe2O4 solid solutions coexisting with the FeO-ZnO system at 1, 100 K show peculiar behavior. The activity of magnetite has a finite non-zero value in pure ZnFe204. The standard Gibbs energy of the reactions at 1.100 K were also obtained as follows:
ZnO (s) + 2/3Fe3O4 (s)+1/602 (g)=ZnFe204 (s), -59090±47J·mol-1 (ZnFe2O4) and ZnO (s)+Fe2O3 (s)=ZnFe2O4 (s), -30160J·mol-1 (ZnFe2O4).
