Development of porous ceramics with graded columnar pore structures via freeze-tape casting
McCrummen, John Drew.
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Freeze-tape casting is a new processing technology that can generate continuous columnar-graded pore structures utilizing a wide variety of ceramic and/or metallic powders. The uni-directional solidification and subsequent freeze drying of yttria stabilized zirconia (YSZ) based aqueous cast tapes is being evaluated for various applications including fuel cells, filtration/separation membranes, and catalyst supports. The degree of pore divergence, pore packing, and pore orientation can be actively tailored by altering the solids loading, freezing rate, and tape pulling speed. The effects of solids loading and freezing rate is discussed with respect to morphology of ice growth. SEM and density data is reported to establish the breadth of tailorability and extent of anisotropy in the frozen tapes. The freeze cast structure of ceramic materials is highly porous. The production of freeze cast, YSZ-based tapes include tap casting techniques and high temperature sintering steps. SEM analysis is displayed at varying angles relative to casting direction to provide further insight of the morphology of these materials. Results of varying solids loading and freezing temperature studies are discussed in detail. Compressive strength data by ASTM standard methods was resultant of concentric ring-on-ring testing and is further explained. Freeze cast structures appear to be potentially desirable over traditional pore formers for various applications.