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.