Hydrolysis and condensation of forsterite precursor alkoxides: Modification of the molecular gel structure by acetic acid

Transparent forsterite precursor gel fibers and monolithic gels could be reproducibly prepared by controlling the hydrolysis-condensation reaction of the precursor alkoxide solution with the appropriate amount of acetic acid. water and ethanol. The time of gelation and the spinnability were strongly dependent on the respective concentrations of water, acetic acid and ethanol, but acetic acid does predominate the spinnability. Infrared study confirmed that acetate anion behaved as a ligand and modified the molecular structure of the gel, playing an important role in the formation of spinnable linear-type polymeric species. Infrared spectra showed that bidentate acetate replaced OR groups and were bounded to metal ions. The acetate ligands were retained in the dried gel fiber and xerogel. A further condensation could occur between silanol groups and decomposition of acetate ligand groups upon heating along with a progressive transformation of the gel structure toward the crystallization of forsterite. The formation of forsterite crystallite commenced at temperature as low as 550 degreesC. The monolithic gel and gel fiber were essentially microporous on heating at 800 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.