Sonogels and derived materials

Abstract

Nowadays the sol–gel process is used by an increasing number of researchers for the preparation of various products, including bulk materials, films, membranes or fibers. The application of ultrasound (sonocatalysis) to the precursors gives rise to materials with new properties, known as sonogels. The absence of additional solvent and, mainly, the effects of ultrasonic cavitation create a unique environment for sol–gel reactions leading to particular features in the resulting gels: high density, fine texture, homogeneous structure etc. These properties determine the evolution of sonogels on further processing and the final material structure. In this sense, the full exploitation of sonocatalysis requires a thorough understanding of the processes involved and their sensitivity to reaction parameters. For this purpose, we have used diverse techniques to investigate the microstructural evolution during different steps in the sonogel process. The results of these studies are reported here. Finally, we present an overview of some applications for which the mechanical, textural and optical characteristics of sonogels are quite useful. Copyright © 1999 John Wiley & Sons, Ltd.