摘要
分别制备了固体电解质8mol%Y_2O_3稳定的ZrO2(YSZ)和Gd_2O_3掺杂的CeO2(CGO),及混合导体材料La0.8Sr0.2MnO3(LSM),借助于X射线衍射(XRD)、交流阻抗谱(EIS)等技术手段对其相组成、导电性能进行了测定;以Co_2O_3为烧结助剂,研究了Co_2O_3对CGO的相组成、烧结性能、导电性能、微观结构的影响。以YSZ为固体电解质,LSM和YSZ的混合物为扩散层,分别采用共压共烧法和丝网印刷法制备了体型和厚膜型氧传感器,对传感器的性能进行研究,并分析了其微观结构。研究结果表明:
YSZ的晶粒、晶界和总电导率与温度的关系均符合Arrhenius公式,在600℃~800℃电导率的数量级为10-3;由固相反应法合成LSM,在23℃~878℃电导率的数量级为100。
由固相反应法制备CGO;分别以Pt和Ag作电极时,晶粒、晶界和总电导率与温度的关系均符合Arrhenius公式;Pt(Ag)/CGO界面阻抗均主要来自氧原子的扩散过程,氧在Pt电极上的扩散是界面扩散过程,而Ag电极兼有体扩散和界面扩散。当CGO中添加2.5wt%Co_2O_3时,1400℃烧结的体密度与1600℃纯CGO的相当,使烧结温度降低200℃。添加0.75wt%Co_2O_3时,试样的晶粒电导率明显增大,晶界电导率下降,添加量为1wt%~2.5wt%时,晶粒电导率趋于不变,晶界电导率稍微有所增加。
分别以LSM掺杂50wt%和60wt%YSZ作扩散层制备的体型氧传感器,在613℃~803℃,氧浓度为0ppm~5.508ppm的范围内,均得到较好的极限电流平台,极限电流与氧浓度存在很好的线性关系;以LSM掺杂20wt%YSZ作扩散层制备的厚膜型氧传感器,在613℃~725℃,氧浓度为0ppm~10ppm的范围内,也得到较好的极限电流平台,极限电流与氧浓度存在较好的线性关系。SEM和EDS结果表明,LSM层与YSZ层结合良好,LSM与YSZ发生了界面反应。
Solid electrolyte Yttria (8mol%) stabilized zirconia (YSZ), Gd_2O_3 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 Co_2O_3, 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% Co_2O_3, 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% Co_2O_3 can increase bulk conductivity of CGO, while grain boundary conductivity reduces. When doping contents of Co_2O_3 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.
引文
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