Of Mgo-al <sub> 2 </ Sub> O <sub> 3 </ Sub>-ysz Department Of Gas Sensing Ceramic Materials Preparation And Performance Research

The YSZ solid electrolyte has been the preferred material of oxygen sensors and fuel battery because of its virtues such as excellent oxygen ion conduction, mechanical property, oxidation-resistance, corrosion-resistance, no reacting with electrode materials and so on. Now more and more researches focus on the research on molding and dopant research of this material. In this work, different amount of MgO and Al₂O₃ as dopant were added into 3mol% YSZ, green body was fabricated by the way of hot injection-molding and gel-molding. The electric properties, microstructure and mechanical properties were carefully studied also.The optimized dispersant and its content, pH value, the volume solid phase content in aqueous slurry were studied through the Zeta potential, sedimentation experiment and slurry viscosity ways. The results show that the optimized pH value of DA dispersant is 10 for YSZ powder and the 54%volume fraction of YSZ aqueous slurries with excellent fluidity can be made ultimately. And for MgO, the viscosity and stability of slurry mixed with YSZ is the best after dispersed by 65/169 dispersant. The organic substance of gel-molding is so low that the degreasing and sintering process can proceed at the same time. And gel-casting can economize time and simplify operation.The sintering schedule was studied by means of material density and SEM analytical ways etc, the result indicated sintering 2h at 1550°C. The electric properties of YSZ solid electrolyte with dopant of MgO or Al₂O₃ were studied by detecting the conductivity and output voltage. It was found that the appropriate amount of oxide dopant could increase the defective density of solid electrolyte, improve crystal grain electrical conduction, and generated reactant with better electric properties by reacting with SiO₂ impurity etc. However, the excessive oxides maybe associate with defectives, impede oxygen vacancy moving at grain boundary so as to reduce the conductivity. The Arrhenius curve between temperature and electric conduction shows the linear property. With the elevated temperature, the activation energy of samples doped with Al₂O₃ raised, especially higher than 550°C. For MA series, conductivity reached a maximum volume with 5mol%MgO and lmol% Al₂O₃.The micro-structures were studied by XRD,SEM and EPM. The results show that the crystal grain of sintering body is relatively ideal, the particles are homogeneously, the partial grains grow up abnormally when the addition is excessive. The XRD indicates that when the MgO doping amount is 8mol%, the sample phase is all cubic. And the micro-structure is quite homogeneous and do not have the segregation and aggregation phenomenon etc.According to the strength and thermal shock-resistance measurements, the tetragonal phase with Al₂O₃ can enhance the strength of materials effectively. The thermal shock-resistance increases with the adding of MgO and reaches the maximum value at 5mol% or so. It can be due to the double-response of zirconium phase changes to the mechanical and thermal shock resistance: volume effect may induce the damage of material, on the other hand the partial produced micro-crack enhance the thermal shock resistance.