Abstract
The alternating reactions of SiCl 4 and H 2O with the surface of Vycor glass have been studied by thermogravimetric analysis at 400-600°C. The results are interpreted by postulating two types of silanol groups (Si-OH) on the Vycor surface, paired and isolated. Reaction of SiCl 4 with paired silanols proceeds by competing steps which control the total extent of silylation. Upon reaction with H 2O, all surface Si-Cl groups are hydrolyzed, reproducing Si-OH. Simultaneous silanol-silanol and silanol-surface chloride condensations eliminate H 2O or HCl to form new Si-O-Si bridges with final product silica. A kinetic model incorporating the silylation, hydrolysis, and condensation steps describes well the TGA data.
Published Version
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