INFRARED STUDY OF SIO2 SOL TO GEL EVOLUTION AND GEL AGING

The evolution of the gelation of silica gel was studied by means of Fo urier transform infrared spectroscopy. The gel was prepared by hydroly sis and polycondensation of tetraethyl orthosilicate in the presence o f water with HCl, and with formamide (DCCA) in methanol either added o r not. For both systems the gelation process was followed by the time evolution of the v-Si-O(H) and v-Si-O(Si) absorption bands. In the sys tems which used formamide, the v-Si-O(H) peak shifts from (v) over til de = 950 cm(-1) for t = 0 to (v) over tilde = 968 cm(-1) (t = t(gel)) and tends to shifts to 975 cm(-1) over a long period of time (t = 100t (gel)), and a slow rate evolution between 0.1 and 0.4 t(gel) is observ ed. In the absence of formamide the same evolution is observed without the slow rate plateau. For v-Si-O(Si) absorption bands, the band near 1075 cm(-1) remains practically unchanged in both systems during the experiment time, but the second absorption band at 1133 cm(-1) is spli t into two bands each having its own specific evolution, depending on composition and temperature.