Thermodynamic Study on the Systems of Metals and Their Oxides by EMF Measurements Using Solid Electrolyte

Abstract

Emf of the following galvanic cell employing solid electrolyte were measured at the temperature range of 700°～1100°C. Pt/Ni · NiO/O--/Air/Pt Pt/Ni · NiO/O--/Cu · Cu₂O/Pt Pt/Ni · NiO/O--/Co · CoO/Pt Pt (Fe · FeO/O--/Ni · NiO/Pt Pt/Fe · Fe₁₋ₓO/O--/Fe₁₋yO · Fe₃O₄/Pt Pt/Ni · NiO/O--/Fe₃O₄ · Fe₂O₃/Pt From those results the equilibrium oxygen pressures of Ni·NiO, Cu·Cu₂O, Co·CoO, Fe·FeO, FeO·Fe₃O₄ and Fe₃O₄·Fe₂O₃, and the standard free energy of formation of NiO, Cu₂O, CoO, FeO, FeO·Fe₃O₃ and Fe₂O₃ were estimated. Based on these experimental results it is shown that 1) stabilized zirconia and thoria could be used as a solid electrolyte under the conditions of 700°～1100°C and partial pressure of oxygen between 1 atm. and 10⁻²⁰ atm., and a little impurity in electrolyte did not have an unfavorable effect on the determination of equilibrium partial oxygen pressure of metal-metallic oxide systems 2) alumina and magnesia could not be used as a solid electrolyte of the present emf measurements 3) one might conclude that emf measurements using a solid electrolyte could obtain the same thermodynamic values as the other reliable equilibrium methods.