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Investigation Of Limiting Current Oxygen Sensors With Dense Diffusion Layer For Automobile Application

Posted on:2008-01-19Degree:MasterType:Thesis
Country:ChinaCandidate:Y Q ZhaoFull Text:PDF
GTID:2178360215455146Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Solid electrolyte Yttria (8mol%) stabilized zirconia (YSZ), Gd2O3 doped CeO2, and mixed-conductor material La0.8Sr0.2MnO3(LSM) were prepared, respectively. The phase compositions and conductance performance of these materials were examined by means of XRD and EIS. The effects of Co2O3, as a sintering aid, on the phase compositions, sinterability, conduction properties and microstructures of CGO were investigated.YSZ was used as material of solid electrolyte and the mixture of LSM and YSZ as diffusion layer, bulk and thick film type oxygen sensors were fabricated by co-pressing and co-sintering and screen printing technique, respectively. The performances of sensors were investigated, and microstructures were analyzed.The results show that the relations of bulk conductivity, grain boundary conductivity and total conductivity of YSZ with temperature all follow Arrhenius equation. The conductivity magnitude grade of YSZ is 10-3 from 600℃to 800℃; the one of LSM prepared by solid state reaction is 100 from 23℃to 878℃.CGO was prepared by solid state reaction; the relations of bulk conductivity, grain boundary conductivity and total conductivity with temperature all follow Arrhenius equation when electrode was Pt or Ag; the interface impedance of Pt (Ag)/CGO mainly comes from diffusion impedance of oxygen, the diffusion of oxygen in Pt electrode is a process of interface diffusion, while the one in Ag electrode is both interface and body diffusion. When doped with 2.5wt% Co2O3, the bulk density of CGO sintered at 1400℃can reach that of pure CGO sintered at 1600℃, the sintering temperature can be reduced by 200℃from 1600℃without aids. Addition of 0.75wt% Co2O3 can increase bulk conductivity of CGO, while grain boundary conductivity reduces. When doping contents of Co2O3 is from 1wt% to 2.5wt%, bulk conductivity goes to invariability, but grain boundary conductivity has a little enhance.The bulk type oxygen sensors, with LSM doped with 50wt% and 60wt%YSZ as diffusion layers, respectively, can both get stable current plateaus in oxygen concentration from 0ppm to 5.508ppm when temperature is from 613℃to 803℃. There is a excellent linear relationship between limiting current and oxygen concentration; the thick film type oxygen sensor, with LSM doped with 20wt% YSZ as diffusion layer, also can get stable current plateaus in oxygen concentration from 0ppm to 10ppm when temperature is from 613℃to 725℃. There is a good linear relationship between limiting current and oxygen concentration. SEM and EDS show that there is a good bonding between LSM layers and YSZ, but there is reaction between LSM and YSZ.
Keywords/Search Tags:oxygen sensor, dense diffusion layer, LSM, doped ceria, sintering aid
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