POTENTIOMETRIC GAS SENSOR FOR CARBON-DIOXIDE USING SOLID ELECTROLYTES

Small insert-type CO//2 sensors are constructed by coating Na//2CO//3 on the one side of a tip-shaped solid electrolyte of NASICON or 'beta'-alumina, and the electromotive force (EMF) is examined at temperatures between 600 and 1000 K. The EMF depends only on the partial pressure of CO//2 and is expressed by the Nernst equation because the activity of Na//2O in the solid electrolytes remains constant. The high activity of Na//2O results in the formation of Na//2CO//3 on the other side of the solid electrolyte tip, giving the EMF to be zero. The response of the sensor is quite rapid. The hybrid CO//2-O//2 sensor is designed by joining the NASICON CO//2 sensor with a stabilized zirconia oxygen sensor. It is revealed by the EMF measurement on the hybrid sensor that the CO//2 sensor functions at oxygen partial pressures above 10** minus **4 Pa.