Effect of Particle Size on the Lamellar Pore Microstructure of Porous Al<sub>2</sub>O<sub>3</sub> Ceramics Fabricated by the Unidirectional Freezing

Abstract

Porous Al2O3 ceramics with a lamellar pore microstructure have been fabricated by a directional freezing process using the micro-sized and nano-sized Al2O3 powders. At the same solid loading and freezing temperature, compared with the suspensions of micro-sized Al2O3, the porous ceramics prepared from the suspensions of nano-sized Al2O3 had the narrower lamellar pore channels and thicker channel walls, which were caused by the higher viscosity, stronger inter-particle attraction and more ice nucleation sites in the nano-sized Al2O3 suspensions. For both types of Al2O3 at a specific solid loading, with the increasing of freezing temperature, the wider pore channels and thinner channel walls were observed. These tendencies were weaker by using the nano-sized Al2O3 . The above results show the lower porosity in the ceramics using the nano-sized Al2O3. However, due to the higher sintering activity for the smaller particles, the pore channel walls by using the nano-sized Al2O3 was denser than using the micro-sized Al2O3, leading to the higher mechanical strength of ceramics.