Fabrication of porous ceramics and composites by a novel freeze casting process

摘要

Porous ceramics have been widely used in many fields. Among the fabrication techniques for porous ceramic, freeze casting has recently attracted much attention as being a versatile, low cost and environmental friendly process. In this study, alumina and Al(_2)O(_3)-ZrO(_2) were utilized as model materials to investigate the preparation technique of freeze casting. Basic factors such as initial solids loading, cooling rate, and sintering temperature that would affect the final morphologies and the effect of additives have been studied. Porous alumina ceramics with lamellar microstructure exhibited compressive strengths up to 123 MPa for 33% porosity and 55 MPa for 42% porosity, making them suitable to be considered for potential load-bearing applications. In a two-phase system (Al(_2)O(_3)-ZrO(_2)), the choice of particle size of the ceramic powder was of great significance, which can lead to engulfment and phase segregation. BaTiO(_3) and Lead zirconate titanate (PZT) were employed to demonstrate the application of the freeze casting technique. BaTiO(_3)-epoxy composites exhibited modest piezoelectric constant but the dielectric constant was 1 order of magnitude higher than conventional composites with randomly distributed ceramic particles. For the 2-2 PZT-epoxy composites, with an increase of initial solids loading from 11 vol.% to 25 vol.%, the volume of ceramic phase in the composite gradually increased from about 30 vol.% to 50 vol.%, the piezoelectric constant (d_{33}) increased from about 103 pC/N to 203 pC/N, demonstrating the potential applications of this technique for the fabrication of 2-2 piezocomposites.