Acoustic emission signals from the sol–gel transition of tetraethoxysilan (TEOS) and sodium silicate solutions

Abstract

Sol–gel processes have been used extensively to prepare oxide materials (glasses and ceramics). The acoustic emission (AE) method with broadband piezoelectric transducer (up to 500 kHz) was used to control the evolution of slow gel formation from organic TEOS and fast formations from sodium silicate as the precursors of silica. The obtained dependencies of the AE count rate and rms values versus time characterize the dynamic of the cross-linking and desolvation processes under ambient conditions. The frequency distribution analysis of individual power spectra provides an activity estimation of integral parts of processes. In sodium silicate solutions the spectra of low frequency (17–70 kHz) were mainly observed. On the other hand, the most representative spectra from the gelation of TEOS display at three basic ranges; 16–20 kHz, 200–230 kHz, and 400–470 kHz. The relative intensities of spectra in these ranges were changed considerably during the gel formation. [Work partly supported by KBN Grant No. T 07B 047 15.]