Study On Matching Of YSZ/Al₂O₃/Pt At Co-Firing High Temperature

The Y₂O₃ stabilized ZrO₂（YSZ）solid Electrolyte NOx sensor can monitor NOx concentration in vehicle exhaust and feed back to the exhaust purification system for catalytic reduction of NOx and reduce the emissions.At present,the working principle,main materials,structure,preparation process and detection method of YSZ solid electrolyte NOx sensor have been studied relatively more in China.The sensor still has some problems such as short service life and poor working stability,due to the poor co-firing matching and interface bonding between YSZ,Al₂O₃ and Pt electrodes.The 5 mol%Y₂O₃ stabilized ZrO₂（5YSZ）green tape was prepared by tape casting process.The 5YSZ solid electrolyte was prepared by warm isostatic pressure and high temperature sintering.The effect of sintering temperature on sintering density and electrical properties of 5YSZ solid electrolyte was studied.It is found that the density of 5YSZ solid electrolyte increases with the increase of sintering temperature.The 5YSZ solid electrolyte sintered at 1450℃ showed the relative higher ionic conductivity than other sintering temperature.The variation of the resistance and grain boundary resistance of 5YSZ solid electrolyte with sintering temperature and test temperature was studied by AC impedance method,and the mechanism of sintering temperature affecting 5YSZ solid electrolyte was analyzed.The relatively better sintering system of 5YSZ solid electrolyte was determined.Two types of sintering aids,MgO powder and glass powder,were used to prepare Al₂O₃ insulation layer slurry.The insulation layer was printed on 5YSZ through screen printing process,and the effect of sintering aids on the sintering characteristics of the insulation layer was studied.Compared with MgO,glass powder can more effectively improve the sintering shrinkage of Al₂O₃ insulation layer,resulting in a relatively flat multi-layer structure of 5YSZ/screen printed Al₂O₃ ceramics after high-temperature co sintering,and improving the high-temperature co-sintering matching of 5YSZ/screen printed Al₂O₃/Pt system.The insulation of 5YSZ/screen printed Al₂O₃ ceramics was tested,and it was found that adding excessive glass powder would weaken the insulation of Al₂O₃ insulation layer.Al₂O₃ tape casting insulation layer was prepared by tape casting process.Al₂O₃ tape casting ceramic sheet was prepared by warm isostatic pressing and high temperature sintering.The influences of particle size,binder content and sintering aid of Al₂O₃ powder on the sintered morphology of Al₂O₃ were studied,and the composition of Al₂O₃ casting slurry was optimized.It is found that the particle size distribution is uniform and the shape rule is beneficial to reduce the defects of Al₂O₃ tape casting ceramic.Increasing the binder content can improve the bonding between Al₂O₃ ceramic particles and improve the sintering densification of Al₂O₃ ceramics.The addition of glass powder further improved the sintering density and sintering shrinkage of Al₂O₃ tape casting ceramic.The 5YSZ/tape casting Al₂O₃/Pt ceramic without cracking phenomenon and with good matching high temperature co-firing was prepared successfully.