Abstract
Reactivities of siloxane bridge formed by thermal treatment of fine silica powder surfaces for water and several aicohols were studied quantitatively. Aerosil 200 as a fine silica powder was thermally treated in vacuum, in the temperature range from 25 to 500°C for 4hrs. The heats of immersion in water of heated silica have a broad maximum at about 300°C. The results of immersional heat suggested that rehydroxylation of siloxane on surface of thermally treated silica dose not completely restore the surface to its original condition. The interesting result obtained by Grignard's reagent test was that the siloxanes, in the all of heat-treated silica, were rehydroxylated by exposure to saturated water vapor for 12hrs. This result was also substantiated by change in the spectra of FT-IR and 29Si CP/MAS NMR. In conclusion, rehydroxylation of siloxane was observed by the heat-treatment ranging from 200 to 500°C. However, for the surfaces treated above 300°C, the reaction rate of rehydroxylation decreased. On the other hand, significant reactions were not observed on a few alcohols.
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