FTIR STUDIES OF GEL TO GLASS CONVERSION IN TEOS FUMED SILICA-DERIVED GELS

Hybrid gels, prepared from mixtures of tetraethyl orthosilicate (TEOS) solution and fumed silica (alkoxide:fumed silica = 1:1.25) were exami ned by FRIR at different stages of drying/densification up to glass fo rmation. Transparent, bubble-free glasses containing low hydroxyl were obtained at up to 1525-degrees-C under vacuum, oxygen, carbon tetrach loride and helium atmospheres. Spectroscopic investigations revealed a free, isolated silanol stretching (nu1) band at around 3740 cm-1 spli t into two to three overlapping peaks after heat treatment of the gels at 600-950-degrees-C. This phenomenon is suggested to be due to eithe r the presence of two types of isolated silanols (single and geminal) and/or an effect of the hybrid microstructure of the gels with widely varying spatial relationships among Si-OH groups, leading to closely r elated, weak interactions.