Fragmentation of SiO2 aerogels in aqueous NaOH solutions studied in situ by SAXS using SR

Structural deformations of three types of silica aerogels due to their diss olution in aqueous solution of NaOH at pH = 13.6-13.9 have been explicitly studied in situ using small angle X-ray scattering of synchrotron radiation . For all aerogels studied the scattered intensity I is found to increase r apidly in the scattering vector range h = 0.15-0.6 nm(-1) that indicates th e aerogel threshold disintegration. When the scattering at h = 0.15 nm(-1) reaches the maximum the dependency of LnI on Lnh gives a straight line with the dope critically depending on the pH of solution and, to a lesser exten t, on the nature of the aerogel. The observed phenomena are discussed in te rms of the percolation theory. (C) 2000 Elsevier Science B.V. All rights re served.