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 dissolution 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 rapidly in the scattering vector range h=0.15–0.6 nm−1 that indicates the 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 slope critically depending on the pH of solution and, to a lesser extent, on the nature of the aerogel. The observed phenomena are discussed in terms of the percolation theory.