RAMAN-SPECTROSCOPIC DETERMINATION OF THE PH-DEPENDENCE OF INTERMEDIATES IN SOL-GEL SILICATE FORMATION

Raman spectroscopy was used to examine the pH and time dependence of the sol-gel hydrolysis and condensation of tetramethyl orthosilicate (TMOS) in aqueous methanol. Tentative band assignments are made for six intermediates in the reaction. Band intensities have been normalized to give composition versus time for each of the intermediates by comparison with nmr results. The time dependence of the generation and loss of the intermediates is highly pH dependent and these measurements show extensive continued reaction beyond the gel print. The Raman spectra of defects in finished silicate glasses are compared to the spectra of the sol-gel intermediates observed here. It is suggested that the defect band D//1 at 484 cm** minus **1 may be associated with the tri-substituted silicate species observed in solution, but that the D//2 band at 608 cm** minus **1 is not related to intermediates observed in the sol-gel process.