KINETIC-STUDY OF THE REACTIONS OF CHLOROSILANES WITH POROUS VYCOR GLASS

The alternating reactions of SiCl4 and H2O 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 SiCl4 with paired silanols proceeds by competing steps which control the total extent of silylation. Upon reaction with H2O, all surface Si-Cl groups are hydrolyzed, reproducing Si-OH. Simultaneous silanol-silanol and silanol-surface chloride condensations eliminate H2O 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. © 1993 by Academic Press, Inc.