Processing of Hierarchical and Anisotropic Porosity LSM-YSZ Composites

Aqueous dispersions of lanthanum strontium manganite (LSM) and yttria-stabilized zirconia (YSZ) particles were controllably freeze-cast and then partially sintered resulting in anisotropic, hierarchically porous ceramics for Solid Oxide Fuel Cell (SOFC) cathodes. The resulting microstructures have aligned pores with a characteristic spacing (λ) between pore centers. The effect of freezing rate, slurry viscosity, and solid loading on solidification velocity and resultant microstructures was explored. Varying these parameters resulted in samples with a range of independently controllable and reproducible microstructures. Homogenous dispersion of LSM and YSZ in the freeze-cast structures was confirmed through elemental mapping. Freezing rate was found to have a significant effect on λ while solid loading affected overall porosity and ceramic wall- to-pore size ratio but had only a small influence on λ. Viscosity was found to have a complex albeit small impact on λ but a significant effect on particle dispersion and colloid stability.