Low Cost Fabrication And Study On Properties Of Yttria-stabilized Zirconia Based Electrolyte

In present paper, the process of zirconia solid electrolyte in solid oxide fuel cell prepared by aqueous gel-casting technique was studied thoroughly. Microstructure and phase configuration were analyzed by XRD, SEM, TEM and so on. The mechanic properties and electric performances of ZrO₂-Y₂O₃ and ZrO₂-Y₂O₃-Al₂O₃ systems were studied thoroughly, these opened up a bright prospect for their industrial applications.Stability and rheological characteristics of aqueous zirconia slurry were studied firstly. The effects of pH value, dispersant, solid loading and milling time on stability and rheological characteristics were determined. The ultimately optimized pH value is from 8 to 10, the content of dispersant is 2% in volume, and milling time is from 20h to 24h. Zirconia aqueous slurries of high solid loading(56vol%) and low viscosity(0.5Pa.s) were first prepared. And YSZ electrolyte thin substrate, which thickness is 200μm and areas are 100×100 mm², was also first fabricated. When sintering is carried out at 1600℃for 4h, crystal boundaries are straight, crystal particles grow rightly and relative density reaches 98.1 percent, these give a base for industrial production.Secondly the effects of some parameters such as temperature, catalyst, humidity and sample thickness on gel forming and drying process were also investigated. Moreover, the distribution of particles in green bodies before and after binder burnt-out was studied. Compared with drying pressing green body, AGC green body has narrow pore distribution and high dispersible particles. Lastly, sintering progress was studied. The results show that sintering temperature, holding time, increasing temperature rate and density of green body have a great influence on sintering progress.The mechanic properties and electric performances of ZrO₂-Y₂O₃ and ZrO₂-Y₂O₃-Al₂O₃ systems prepared by aqueous gel casting method were also studied in this thesis. Results show that bending strength and fracture toughness of Al₂O₃-YSZ increase with increasing alumina content. Bending strength increases firstly, then decreases with increasing yittra content, but fracture toughness decreases straightly. When yittra content is 3 mol percent. bending strength reaches as high as 891MPa and fracture toughness is 9.2 MPa·m^1/2, its general mechanic properties are best of all.Ionic electric conductivity increases firstly, then decreases with increasing yittra content. Electric conductivity increases with increasing temperature, and is linearity. Ionic electric conductivity also increases firstly, then decreases with increasing alumina content. Electric conductivity of 1 weight percent ratio-YSZ is higher than that of YSZ. Ionic electric conductivity of zirconia solid electrolyte thin substrate using aqueous gel casting technique reaches 0.15 S/cm at 1000℃, and its activation energy for ionic conduction is 0.821eV. This provides the possibility of applications.