Fabrication of porous alumina by directional freeze casting and annealing in TBA–water–sucrose system

Abstract

The volume change difference between water and tert-butyl alcohol (TBA) hydrate was approximately 10.1% when ceramic slurry with water–TBA was frozen for fabrication of porous ceramics. Residual stress may be produced at the pore walls and led to low compressive strength of the ceramics. In this regard, sucrose was used in the ceramic slurry. Several water–TBA crystals were observed in the sucrose amorphous bodies after directional freezing. Water and TBA in the sucrose amorphous bodies were recrystallized during subsequent annealing. Sucrose was used as a protective agent and annealing additive in the TBA–water–sucrose system to eliminate residual stress and change the pore structure from snowflakes and dendrites into tiny cylinders. Adding sucrose and annealing process exerted minimal effect on the open porosity of porous ceramics but remarkably improved their compressive strength. When TBA and sucrose contents were 30 and 20 wt%, respectively, in the ceramic slurry with 20 vol% alumina content, the compressive strength of porous ceramics was 49.9 MPa after annealing at − 15 °C for 2 h. The value was 3.6-fold higher than that of the ceramic without annealing. Results provide a new method for improving the mechanical properties of porous ceramics prepared by freeze casting.