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We developed a novel and simple bidirectional freeze-casting technique to prepare porous ceramics with long-range ordered lamellar structures in three dimensions (3D). A side copper or stainless-steel plate was used as the cold source to generate dual temperature gradients for the control of the nucleation and growth of ice crystals. The Al 2 O 3 architectures prepared with the side copper plate exhibited well-assembled lamellar structures with abundant cross connections of the ceramic lamellae. The compressive strength of the resultant Al 2 O 3 architectures with ∼ 50% porosity reached 158 ± 3 MPa in the primary freezing direction and 42 ± 6 MPa in the secondary freezing direction, ∼ 32% and ∼ 130% higher than that of the counterparts prepared by unidirectional freeze casting. In contrast, the Al 2 O 3 architectures prepared with a side stainless-steel plate exhibited thicker ceramic lamellae and wider pore channels as well as decreased cross connections, leading to much weaker compressive strength. [ABSTRACT FROM AUTHOR]

Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al 2 O 3 −ZrO 2 composites with initial ceramic loading of 30 vol% and different Al 2 O 3 :ZrO 2 weight ratios (Al 2 O 3 :ZrO 2 =1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al 2 O 3 −ZrO 2 scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al 2 O 3 content. During pressureless infiltration, multiple chemical reactions took place between ZrO 2 and the Al−12Si−10Mg alloy and the main reaction products were (Al 1−m , Si m ) 3 Zr, Al 2 O 3 and ZrSi 2 phases. The degree of the reaction depended on the ZrO 2 content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al 2 O 3 content, but three-point bending strength showed a first decrease and then increase. When Al 2 O 3 :ZrO 2 =1:9, the compressive and bending strength of the composites reached about 997±60 MPa and 426±10 MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites. [ABSTRACT FROM AUTHOR]