IONIC-CONDUCTIVITY OF MALSI2O6 (M = LI, NA, K, RB AND CS) AND ITS APPLICATION AS A POTENTIOMETRIC CO2 GAS SENSORS

Five kinds of alkali-metal aluminosilicate ceramics, MAlSi2O6 (M=Li, N a, K, Rb or Cs),were prepared by sintering a mixture of M2CO3, Al2O3 a nd SiO2, and their properties as a solid electrolyte were investigated by designing a series of solid electrochemical cells such as (-)CO2, O-2, Pt \MAlSi2O6\Au, M2CO3, CO2, O-2(+), for the CO2 gas sensor, wher e MAlSi2O6 functions as an alkali-metal ionic conductor. Electromotive force, EMF, increased linearly with an increase in the logarithmic va lue of carbon dioxide partial pressure, in accordance with the Nernst' s law and the slope of the Nernst's equation suggests two electron rea ction of carbon dioxide molecule at the detection electrode around 400 degrees C. At this temperature, the 90% response times were about 1 m in for all of the sensors. The sensor prepared KAlSi2O6 as the solid e lectrolyte was found to work at the lowest temperature and over the wi dest temperature range.