Preparation of γ -alumina foams of high surface area employing the polyurethane sponge replica method

Single phase γ-Al₂O₃ ceramic foams with high surface area (~180 m² /g) and porosity (67%) were prepared by the polyurethane sponge method from slurries containing γ-Al₂O₃ (~40 wt % of solids). Different commercial polyurethane sponges were tested as templates for the ceramic foams, and the better results were obtained with a hydrophilated polyester polyurethane with pore density of 122 ppi, and thermal behavior that suggested the presence of fire retardant and smoke suppressor additives. The mechanical strength of the ceramic foams depended on several factors, such as the chemical nature of the sponge employed as template, composition of the slurry, and the heating rate duringcalcination. It was found that at least four cycles of recoating followed by drying were required before calcination to prevent collapse of the ceramic foams.