Fabrication of Bulk Lamellar Porous Ceramic Using Unidirectional Freeze Casting Method

Abstract

Freeze casting or ice-templating is an emerging technique used to fabricate highly porous ceramic scaffold having lamellar pore morphology. The growing ice crystals triggers the self- assembly of ceramic particles hence produces a large, anisotropic porous material. Water based ceramic suspension containing α-Al2O3 platelets was used to form a large porous scaffold by unidirectional freeze casting having pores that are negative replica of ice crystals. Well dispersed hexagonal shaped α-Al2O3 platelets having diameter and thickness varies in between 8 – 9 μm and 1 – 2 μm respectively, were synthesized by flux method using boehmite as a precursor for alumina. Aqueous ceramic slurry was prepared with these platelets and allowed for controlled freezing in a custom made freeze casting device followed by sublimation in a conventional freeze dryer results in formation of layered ceramic porous scaffold. Pressing the green body in a direction perpendicular to the ice front growth direction with subsequent sintering at 1500o C for 4h results a partially dense body. The microstructural study of this partially dense material shows large scale parallel alignment of α-Al2O3 platelets. This newly developed high porosity mechanically strong material has potential application in energy related areas and several structural applications.