A galvanic sensor for {SO_3 / SO_2} based on the {CaF_2 / CaSO_4} couple

Measurements on the solid state cell, {Pt/O^\prime _2} + {SO^\prime _2} + {SO^\prime_3 / CaF_2} + {CaSO_4} \|{CaF_2} \| {CaF_2} + {CaSO_4 / O^{\prime\prime}_2 + SO^{\prime \prime}_2 + SO^{\prime \prime}_3 / Pt} using single crystal {CaF_2} as the solid electrolyte and {CaSO_4} as an auxiliary electrode, indicate that the EMF is in agreement with that predicted by the Nernst equation when equilibrium is assumed in the gas phase near the electrodes. The cell can be used to measure the {SO_2 / SO_3} content of gases at temperatures near 1200 K, where approximately 2 h ate required to obtain a steady EMF, without the use of catalysts to improve the kinetics of exchange reaction in the auxiliary electrode. For most applications, the cell EMF will be affected by the presence of water vapour in the gas phase. The cell is well suited for thermodynamic measurements on sulfates, pyrosulfates and their solid and liquid solutions