Fabrication of Ultra-Lightweight and Highly Porous Alumina Scaffolds by a Novel Sol–Gel/Freeze Casting Hybrid Method

Ceramic-based scaffolds developed by the freeze casting method exhibit anisotropic lamellar and interconnected porous structure and can be adopted for filtration, insulation, absorption, and many applications. However, the upper limit of porosity caused by the unstable mechanical properties from low solid-loading slurries has restricted functionalities of scaffolds fabricated by the traditional freeze casting method. In this study, the sol–gel/freeze casting hybrid method was developed to fabricate the alumina scaffolds with low bulk density (200–500 kg/m³) and proper specific strength. The microstructural features of the lamellar structure and continuous surface developed from the condensation reaction were evaluated by SEM. The ultra-lightweight porous alumina scaffolds successfully fabricated by this hybrid method show high specific surface area and proper mechanical stability. The porosity of alumina scaffolds can reach over 90%, possessing great potential for filtration and gas absorption applications in the future, and this hybrid sol–gel/freeze casting approach can be extended to ceramic/glass scaffolds with varying functionalities.