Thermodynamic Study of Spinel Type Solid Solutions of the Fe₃O₄–ZnFe₂O₄ System by E.M.F. Measurements using the Solid Electrolyte

Abstract

The e.m.f. of the following galvanic cells with a ZrO₂+CaO solid electrolyte has been measured in the temperature range of 850–1050°C in the whole composition range of spinel type solid solutions of Fe₃O₄–ZnFe₂O₄.
(−)Fe₃O₄, Fe₂O₃/ZrO₂+CaO/(Fe₃O₄)_x(ZnFe₂O₄)_1−x, Fe₂O₃(+)
(−)Ni, NiO/ZrO₂+CaO/(Fe₃O₄)_x(ZnFe₂O₄)_1−x, ZnO(+)
The activities of Fe₃O₄ were derived from the e.m.f. according to a new analytical method. In the solid solutions coexisting with the Fe₂O₃, a_Fe3O4 curve shows a small positive deviation from Raoult’s law in the ZnFe₂O₄-rich range, and obeys Raoult’s law in the Fe₃O₄-rich range. In the solid solutions coexisting with ZnO, the a_Fe3O4 curve shows a large positive deviation from Raoult’s law in the whole composition range and a_Fe3O4 has a finite non-zero value in pure ZnFe₂O₄. Equilibrium oxygen partial pressures for the solid solutions coexisting with Fe₂O₃ or ZnO were calculated from the experimental results. These results were compared with published data.