1984 年 5 巻 Special 号 p. 262-269
Alkali metal sulfates are basically applicable to SOx sensors as solid electrolytes. The electro-motive force (emf) of the solid electrolyte cells is expressed by the Nernst equation. The lowering of the emf is noticed at a large SOx pressures difference between the anode and the cathode. This is caused by the physical permeation of gases in the electrolyte through cracks and pores which arise from volume change during the III-I phase transition and from low sinterability, The use of NASICON (Na3Zr2Si2PO12) which is easily sintered to high densities provides an SOx sensor with no permeability. The generation of emf is essentially due to the formation of Na2SO4 both on the anode and on the cathode. The solid reference electrodes for SOx sensors are reviewed briefly. A small insert-type CO2 sensor has been constructed using Na2CO3 with a tip of NASICON or β-alumina, and is proved to function satisfactorily. The activity of Na2O in NASICON or β-alumina is taken as a reference state in this sensor.