Chem. Mater., 9 (11), 2418 -2433, 1997. cm9703684 S0897-4756(97)00368-2

Copyright © 1997 American Chemical Society

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

Rhonda L. Callender,^1a C. Jeff Harlan,^1a Noah M. Shapiro,^1a Christopher D. Jones,^1a Daniel L. Callahan,^1b Mark R. Wiesner,^1c D. Brent MacQueen,^1d Ron Cook,^1d and Andrew R. Barron*^1ab

Department of Chemistry, Rice University, Houston, Texas 77005; Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas 77005; Department of Environmental Science and Engineering, Rice University, Houston, Texas 77005; and TDA Research, Inc., 12345 West 52nd Avenue, Wheat Ridge, Colorado 80033

Received May 16, 1997

Revised Manuscript Received August 19, 1997

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(O₂CR)_z]_n, were synthesized by the reaction of boehmite, [Al(O)(OH)]_n, with acetic acid (HO₂CCH₃), methoxyacetic acid (HO₂CCH₂OCH₃), (methoxyethoxy)acetic acid (HO₂CCH₂OCH₂CH₂OCH₃) and [(methoxyethoxy)ethoxy]acetic acid [HO₂CCH₂(OCH₂CH₂)₂OCH₃]. 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.

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