The Study Of The Oxygen Sensor With Planar Structure Based On La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85

Recently, oxygen sensors as an oxygen concentration monitoring device has gained more andmore attentions, especially plays a key role in the automobile exhaust emission control system.Currently, the oxygen sensor market was mainly occupied by zirconia-based oxygen sensors.However, the working temperature of the oxygen sensor has to be above800℃, which may causesome problems, such as the high power dissipation, hardly seal, difficult to select the matchedelectrode materials and so on. In order to reduce the sensor’s working temperature, oxide ionconductor-La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85working at intermediate temperatures was applied to fabricatethe oxygen sensors. Initially, the properties of the La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85（LSGM） sintered atdifferent temperatures were studied. Then, the LSGM-based potentiometric oxygen sensor andamperometric oxygen sensor attached with a thin hole diffusion barrier or an ionic diffusion barrierwere fabricated. Finally, the sensing performances of these oxygen sensors were evaluated atdifferent conditions. The research details and obtained results were shown as below:First, a general introduction of this thesis, technical rote, innovations, reagents, testingmethods and equipments were introduced.Second, after the La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85powder were pre-calcined at1000℃for1h andmolded to cylinders, the samples were sintered at six temperature points （1250～1500℃,with theintervals of50℃） for4h, respectively. Then, some tests were taken to these obtained samples, suchas the relative density, linear shrinkage, XRD, SEM, impedance spectroscopy and ionicconductivity. The characterization results showed that the sample which was sintered at1400℃exhibited the best performance that of other samples. Tightly arranged gain and superficialnonporous microstructure can be found for sample sintered at1400℃, with its relative density was96.6%. In the meantime, the XRD pattern indicated that the sample only contained theLa_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85signal crystal phase. Moreover, its ionic conductivity at differenttemperature points （450～800℃,with the intervals of50℃） were all the highest, which was0.093S/cm at800℃. Therefore, the La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85solid electrolyte sintered at1400℃was believed to be more suitable for the fabrication of the oxygen sensors than other samples.Third, the potentiometric oxygen sensor was fabricated based on the La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85solid electrolyte which was sintered at1400℃. From the relation graph of oxygen concentration and excess air ratio which were tested at600℃,650℃and700℃., it can be found that thevoltages changed suddenly where the excess air ratio was nearby1. This phenomenon was wellmatched the characteristics of the potentiometric oxygen sensor.Fourth, the La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85solid electrolyte sintered at1400℃was applied tofabricated the amperometric oxygen sensor with a thin hole diffusion barrier. The oxygen sensorexhibited good performance at600℃and650℃. The desirable limiting current platforms wereexhibited with the oxygen concentration ranged from0.1%to3%. And, the limiting current andoxygen concentration showed a satisfied linear relationship. In addition, the rise and fall responsetime of the oxygen sensor at650℃were about15s.Fifth, a new amperometric oxygen sensor with an ionic diffusion barrier was fabricated basedon La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85solid electrolyte. According to the working principle of this oxygensensor, the Faraday’s first law, Fick’s law and Langmuir adsorption equation, the relationshipbetween the limiting current and oxygen concentration was thoroughly studied. The deduced resultindicated that the ratio of the oxygen concentration and limiting current exhibited a lineardependence on oxygen concentration. When the tested temperature was at600℃or650℃, thedesirable limiting current platforms were discovered with oxygen concentration in the ranged of1%to100%. The relationship between the limiting current and oxygen concentration that wasobtained from the results was consistent with the theoretical deduced result. Additionally, the riseand fall response time of the oxygen sensor at600℃were around10s.