XEROGELS, A PROCESS FOR THEIR PREPARATION, AND THEIR USE

摘要

The invention relates to modified SiO2 gels (xerogels), the preparationthereof and the use thereof as thermal insulators. The xerogels are prepared by acidifying an aqueous waterglass solution, polycondensing the silicic acid produced thereby, by adding a base, to an SiO2 gel, removing the water from the resulting gel by extractive distillation with an organic solvent which forms with water an azeotrope which separates on cooling into two phases, reacting the gel with a silylating agent, and then drying at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used for removing the water.