Preparation of high porosity xerogels by chemical surface...

Details Preparation of high porosity xerogels by chemical surface... Preparation of high porosity xerogels by chemical surface...

C - Chemistry, Metallurgy

01

B

C01B 33/16 (2006.01) B01J 13/00 (2006.01)

Patent

CA 2160993

This invention provides an extremely porous xerogel dried at vacuum to below-supercritical pressures but having the properties of aerogels which are typically dried at supercritical pressures. This is done by reacting the internal pore surface of the wet gel (e.g. alkoxide- derived silica gel) with an organic surface modification agent (e.g. trimethychloro-silane in benzene) in order to change the contact angle of the fluid meniscus in the pores during drying. Shrinkage of the gel (which is normally prevented by the use of high autoclave pressures, such that the pore fluid is at temperature and pressure above its critical value) is avoided even at vacuum or ambient pressures. The figure 4 shows a change in sample weight and sample length during drying for surface modified, ambient pressure gel processed in accordance with the invention, illustrating the initial shrinkage followed by expansion of the gel during the final stages of drying. The extremely low density finely pored gel products have useful insulating and other properties.

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