Study On CeO₂-based Limiting Current Oxygen Sensor With A Dense Diffusion Barrier By Spark Plasma Sintering

Solid electrolyte is the key materials of oxygen sensor. It decides the working temperature andother properties of sensor directly. The sensitive material of limiting current oxygen sensor ismainly composed of YSZ presently. In this paper，in order to improve working temperature，energy costing and matching problems，Gd doped CeO₂-based solid electrolyte was used assensitive material to replace the traditional material YSZ. A series of researches on materialproperties and sensor fabricating were done. In the meantime，Spark Plasma Sintering was appledto prepare solid electrolyte. Effect on the phase and micro Morphology of electrolyte underdifferent sintering conditions was analysed and discussed.Gd doped CeO₂(Ce_0.8Gd_0.2O_1.9，CGO) was used as solid electrolyte. The CGO was sinteredin conventional way after dry-pressing. The physical properties as line shrinkage rate，relativedensity，phase and micro-morphology of the sintering samples were analysed. The conductivity ofthe samples was measured by the method of AC Impedance Spectroscopy. The CGO was basicallymeat the requirements of solid electrolyte used in oxygen sensor.Based on above analysis，for better matching attribution between the dense diffusion barrierlayer and the sensitive layer，same solid electrolyte material was used and a special type oflimiting current oxygen sensor with a dense diffusion barrier was prepared. According to the test ofthe sensitive property to oxygen，the sensor showed better limiting current property in highoxygen concentration. Through the analysis of working principle of the sensor，a relatedtheoretical model was established，which can explain the relationship between the limiting currentand the oxygen concentration of this sensor well.Different limiting current oxygen sensor were prepared with LSM，LC（LSM and CGOmixed at different mass ratio）and3Y as diffusion barrier material，respectively. The I-Vproperties of the sensors were tested and analyzed. The sensor with LC30（LSM and CGO mixedat mass ratio7:3）as its diffusion barrier had a relatively better limiting-current plateform when theoxygen concentration was in the range of1.06%to1.84%. The limiting current and the oxygen concentration of this sensor fit the the oretical model we established before. It also had a quickresponse-time. However，the other sensors didn’t have ideal limiting current properties.To have better material properties，a preliminary study on CGO by Spark Plasma Sinteringwas made. Effect on micro-morphology and other properties caused by difference sinteringparameter was discussed. In order to avoid the problems of crazing and low density，a bettersintering system need to be found.To promote development and manufacturing of the oxygen sensor used in cars，wedeveloped a mass testing system. This system simulate the exhaust emission environment in car.Key performance parameters of oxygen sensor can be measured by changing atmosphere. It is acomplete set of producing and testing system and has characteristics of convenient，fast andefficient.