Freeze-cast porous Al2O3 ceramics strengthened by up to 80% ceramics fibers

Porous ceramics with oriented pores have wide applications in the fields of filtration, insulation, biomaterials, and catalysis. In the present work, strengthening effect of up to 80% Al2O3 fibers in freeze-cast porous Al2O3 ceramics was studied. The effect of Al2O3 fiber on the slurry viscosity, shrinkage, porosity, pore morphology, and compressive strength was systematically investigated. Both fiber bridge structure and fiber-containing wall structure are formed in the porous ceramics because of the incorporating Al2O3 fibers. The formation mechanisms of these two structures were explored through analyzing the interaction between fibers and solid-liquid interface. Both porosity and structural wavelength of porous ceramics increase with the increase in fiber content. The pore morphology varies from lamellar to dendritic then to isotropic as the fiber content increasing. Adequate addition (20–40 vol%) of Al2O3 fibers in the slurry is capable of improving the compressive strength, while excess fibers would deteriorate the compressive strength. The strengthening mechanism was studied through observing fracture morphology and failure mode.