Isotropic freeze casting of through-porous hydroxyapatite ceramics

It has well known that hydroxyapatite(HA) is a kind of excellent materials for biomolecular absorption and separation, and the absorption and separation performances of HA would be improved if HA had been processed into desirable porous structures. In this paper, we reported on the combination of gel casting and freeze casting to develop the through-porous hydroxyapatite ceramic monoliths. Experiments demonstrated that the gel-containing freeze casting technique was an isotropic pore-forming technique and could prepare the near-net-shape forming green bodies with good mechanical strength no matter what the HA content in green bodies was. Further green body sintering formed the through-porous ceramics whose grain size, pore size, and porosity depended on and could be controlled by the content of HA in green bodies. The formation of through-pores in ceramics resulted from the gels and water in green bodies, which acted as the templates of the pores with size < 1 μm and the pores with size > 1 μm, respectively. The gel–freeze casting technique is simple, repeatable, and cost-effective, therefore being hopeful for industrial applications.