Fabrication of ceramics with complex porous structures by the impregnate-freeze-casting process

The ceramics with complex porous structures were fabricated by a combination of impregnating and freeze-casting process. The polyurethane sponge was impregnated in the mold with 20 vol% of aqueous alumina slurry, and then the bottom of the cast body was kept at a constant cooling rate of 6°C/min to induce unidirectional solidification. After drying and sintering of the green part, porous ceramic with obvious lamellar architectures was prepared. The lamellae thickness and interlayer distance were as large as ∼9 and ∼15 μm, respectively. The large pores, which resulted from the burn-up of sponge struts were homogeneously distributed in the sample. The use of the porous template introduced some local interruption of the lamellar structures. However, high compression strength for the porous ceramic can still be obtained.