Performance of YSZ Oxygen Sensors Protected by Electrochemical Filters

The performance of nernstian Yttria Stabilized Zirconia (YSZ) oxygen sensors can be seriously affected when in contact with some aggressive industrial furnace atmospheres. Longer life time can be obtained for sensors protected with electrochemical filters. The most relevant parameters determining the protected sensor performance are the ratio between the sensor and the filter oxygen electrochemical permeabilities, and the volume of the electrode protection chamber. The ratio between materials electrochemical permeabilities determines the sensor oxygen activity applicability domain and the deviation between the effective (steady state) and desirable (theoretical) sensor reading. The protected chamber volume will influence the time response behavior. Theoretical predictions on sensor performance are compared with experimental data obtained for protected YSZ sensors conceived for moderately oxidizing atmospheres (1 Pa< Po(2) < 21 kPa). Two different cases are studied including one single phase and one composite (ionic + electronic conductor) electrochemical filter.