Dissociation Pressures of Metal Sulfates by Electromotive Force Measurement on SO2–O2–SO3Concentration Cells with Nasicon Solid Electrolyte

Dissociation pressures of nickel, magnesium and copper sulfates have been measured by the electromotive force measurement of the SO2–O2–SO3 concentration cell using NASICON as a solid electrolyte. The standard free energy changes for the dissociation are obtained as follows:NiSO4 = NiO + SO3,∆G0/J mol−1 = (2.432 ± 0.024) × 105 − (1.949 ± 0.027) × 102T (776–1069 K)MgSO4 = MgO + SO3 ∆G0/J mol−1 = (3.033 ± 0.085) × 105 − (1.937 ± 0.085) × 102T (932–1066K)and CuO·CuSO4 = 2CuO + SO3 ∆G0/J mol−1 = (2.315 ± 0.037) × 105 − (1.864 ± 0.040) × 102T (802–1062 K).The three-phase coexisting mixture of Cu2O–CuO–CuO·CuSO4 is recommended as the solid reference electrode for a potentiometric solid electrolyte SO x sensor.