Aqueous Synthesis of Water-Soluble Alumoxanes:  Environmentally Benign Precursors to Alumina and Aluminum-Based Ceramics

Abstract

The objective of our research is the development of an environmentally benign process for the fabrication of alumina-based ceramics. We have designed an alternative synthetic pathway to alumina ceramics that does not utilize toxic reagents or volatile organic chemicals (VOCs); the aqueous synthesis of “water-soluble” carboxylate−alumoxane precursors from inexpensive boehmite feed stock. Carboxylate−alumoxanes, [Al(O) x (OH) y (O 2 CR) z ] n, were synthesized by the reaction of boehmite, [Al(O)(OH)] n, with acetic acid (HO 2 CCH 3 ), methoxyacetic acid (HO 2 CCH 2 OCH 3 ), (methoxyethoxy)acetic acid (HO 2 CCH 2 OCH 2 CH 2 OCH 3 ) and [(methoxyethoxy)ethoxy]acetic acid [HO 2 CCH 2 (OCH 2 CH 2 ) 2 OCH 3 ]. Carboxylate−alumoxanes are infinitely stable at ambient conditions in solid and solution. In addition, they show no propensity to segregation or polymerization and are readily processed in aqueous or hydrocarbon medium. Upon thermolysis the carboxylate−alumoxanes are converted to alumina. The physical and spectroscopic properties of the carboxylate−alumoxanes have been determined, including particle size, molecular weight, hardness, refractive index and dielectric constants. The application of the carboxylate−alumoxanes as preceramic binders in traditional tape casting, and infiltration agents has been demonstrated. The potential environmental impact of the new alumoxane methodology as compared to traditional approaches will be discussed.