Spontaneous formation of nano-fibrillar boehmite and the enhancement effect of polyethylene glycol

Abstract

Nano-fibrillar boehmite is a desirable product due to its high specific surface area and potential application in a wide variety of engineering applications. Inorganic salts are the preferred raw materials for fabricating such products because of their low cost. In this study, nano-sized (10-20 nm in diameter) boehmite fibrils were fabricated by the hydrothermal (105°C) digestion of a suspension prepared from either aluminum sulfate or nitrate salt under a neutral pH. It appears that the formation of fibrils is spontaneous and thermodynamically favorable. The presence of polyethylene glycol (PEG) was found to further enhance the formation of fibrils by promoting the transportation of aluminum ions to the crystal nuclei. The growth direction of the crystals in the fibrils is normal to the boehmite (020) plane. The formation of boehmite fibrils was greatly reduced under an acidic pH and at a lower digestion temperature due to kinetic restriction. The structures of the immediate products generated from aluminum sulfate and aluminum nitrate were different, which is probably due to the stronger adsorption of sulfate ions on the surface of gelatinous aggregates. The fibrils derived from as-precipitated and coagulated amorphous aluminum hydroxide grains experienced a series of structural evolutions in which they progressed from a sponge-like structure to a fibrillar structure with time. © 2011 The American Ceramic Society.