Preparation And Oxygen Sensing Characteristics Of Limiting Current Oxygen Sensors With Dense Diffusion Barriers

Wide range air-fuel ratio and limiting current zirconia oxygen sensors are one of the major trends in the development of the automobile exhaust sensors. They can be used to improve fuel energy and reduce automobile exhaust pollution. The performance of the aperture type of limiting current oxygen sensors and the porous layer type of limiting current oxygen sensors will be influenced through long time use, because the hole of the first type of sensors will occlude easily and the porosity of the porous layer of the second type of sensors will change during long term operation. We also known that concentration-zirconia oxygen sensors need to reference gases, which detect high oxygen concentration is not very accurate. These problems may be overcame by using a mixed electronic and oxygen ion-conduction solid diffusion barrier.In the paper, LaBMO3 (B=Sr, Ca, Ba) is used as materials of dense diffusion barrier of sensors and Yttria (8%mol) stabilized zirconia (YSZ) is used as materials of solid electrolyte layer, and dense diffusion barrier limiting current oxygen sensors are prepared by ceramic composite process and test oxygen sensitivity.Mixed electronic and oxygen ion-conduction solid diffusion barrier (LaBMO3) is prepared by high-temperature solid-phase synthesis. Milling process, powder calcining temperature, forming process, sintering temperature, density and high temperature conductivity are studied in the experiment systemtically. Diffusion barriers (La_0.8Sr_0.2MnO₃) with high density (ρ=5.9g/cm³) and high conductivity (σ>10^-1s/cm) are prepared.Yttria (8%mol) stabilized zirconia (YSZ) is prepared by chemical coprecipitation method. We mainly study its powder calcining temperature,ceramic sintering temperature, soaking time, density and high temperature resistance. YSZ with high density (ρ=5.6g/cm³) and high temperature conductivity(σ>10-2s/cm) are prepared.Dense diffusion barrier layer and sintered YSZ are bonded by ceramic composite process, and sealing are carried out by glass materials, and then dense diffusion barrier layer limiting current oxygen sensors are fabricated. Sensors fabricated with this method have preparation of simple, controllable process, good tightness, no problem of co-sintering and their dense diffusion barrier layers have enough thickness.Oxygen sensitivity is tested by limiting current oxygen sensor testing equipment. The results show that the oxygen measure range of sensors fabricated with this method is from 0%-21% and the stable limiting current platform (I_max=12mA) is get. Voltage range is from 0.6v to 1v when the liming current appears. Relation of oxygen concentration and limiting current is exponential function. There is detection of high precision; especially in the high concentration of oxygen atmosphere (it can reach 0.1%) in the sensors. The sensor offer strong stability performance and high sensitivity of the sensor and fast reaction time about 10 seconds. Study of the issue provides the theoretical and experimental basis for the practical application of this oxygen sensor.