PERFORMANCE OF PROTECTED OXYGEN SENSORS .1. SINGLE-PHASE MIXED CONDUCTING FILTERS

Theoretical predictions on sensor performance are compared with experimental data obtained for YSZ (yttria stabilized zirconia) sensors protected by different types of single phase mixed conductors, including materials usually identified as predominantly ionic or electronic conductors. Relevant parameters determining the protected sensor performance are the ratio between the sensor and the filter oxygen electrochemical permeabilities, the volume of the electrode protection chamber, the temperature and the magnitude of the oxygen pressure being measured. The sensor to filter electrochemical permeability ratio determines the steady state deviation between the protected and unprotected sensor reading. Decreasing the protected chamber volume and the magnitude of the oxygen partial pressure being measured will determine a faster sensor response. Results now reported, corresponding mostly to slow sensor response, are strongly determined by the relatively low operating temperatures (850-950 degrees C) used in these laboratory scale experiments, but can be optimized for industrial applications.