480581 Sinterable and Printable Al2O3-Doped YSZ for Advanced SOFC Electrolytes

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Maila Kodas1, Christopher J. Bartel2, Alan W. Weimer3, Austin Drake1 and Rebecca O'Toole1, (1)Chemical and Biological Engineering, University of Colorado at Boulder, Boulder, CO, (2)Chemical & Biological Engineering, University of Colorado, Boulder, CO, (3)Chemical & Biological Engineering, University of Colorado at Boulder, Boulder, CO

Yttria-stabilized (8 mol %) cubic zirconia (8YSZ) has practical uses as an ion conducting electrolyte in solid oxide fuel cells, but suffers from some inherent shortcomings such as low ionic conductivity at moderate temperatures, high sintering temperature, and poor mechanical strength. The addition of alumina (Al2O3) has been shown to lower the sintering temperature while increasing mechanical strength and ionic conductivity. Al2O3 aids in sintering kinetics and densification by altering the mechanism by which the particles sinter together. In order to study the mechanisms occurring during sintering, a Master Sintering Curve (MSC) approach was used. MSC’s allow for prediction of densification results and allow insight into the sintering kinetics by relating the activation energy of sintering to density, regardless of heating regimen. The effects of varying Al2O3 additions on sintering behavior and kinetics were studied and compared to undoped 8YSZ. Doping with Al2O3 was found to substantially improve densification behavior including the onset temperature for densification and the temperature at which the densification rate was maximized. Al2O3 additions between 0 and 3 wt % were studied for comparison. Scanning electron microscopy (SEM) was used to evaluate grain growth at varying stages of densification to gain insight into the mechanisms of sintering. Additionally, a colloidal ink was formulated using the doped and undoped 8YSZ powder for the purpose of direct ink writing. Direct ink writing is the process of extruding an ink through a small nozzle in a controlled manner in order to systematically print a 3D architecture. The ink formulation was engineered with maximum solids loading while maintaining the desired rheology. That is, the solids (ceramic) incorporation was optimized to minimize warping upon drying and sintering while maintaining a flowable suspension. The ink was then used to print 3D lattice structures that were then sintered, resulting in complex parts with ~200 micron feature sizes.

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