Effect of ZrO₂ (9mol% Y₂O₃) coating thickness on the electronic conductivity of Mg-PSZ oxygen sensors

The ZrO₂ (9mol% Y₂O₃) coating was prepared evenly on the surface of MgO partially stabilized zirconia (Mg-PSZ) tube (oxygen sensor probe) by dipping the green Mg-PSZ tube in a ZrO₂ (9mol% Y₂O₃) slurry and then co-firing at 1750°C for 8 h. The double-cell method was employed to measure the electronic conductivity parameter and exam the reproducibility of the coated Mg-PSZ tube. The experimental results indicate that the good thermal shock resistance of the Mg-PSZ tube can be retained when the coating thickness is not more than 3.4 μm. The ZrO₂ (9mol% Y₂O₃) coating reduces the electronic conductivity parameter remarkably, probably due to the lower electronic conductivity of Y₂O,-stabilized ZrO₂ than that of MgO-stabilized ZrO₂. Moreover, the ZrO₂ (9mol% Y₂O₃) coating can improve the reproducibility and accuracy of the Mg-PSZ tube significantly in the low oxygen measurement. The smooth surface feature and lower electronic conductivity of the coated Mg-PSZ tube should be responsible for this improvement.