| abstract |
The invention relates to modified SiO₂ gels (xerogels), their preparation and their use as heat insulation agents. The xerogels are prepared by acidifying an aqueous water glass solution, the resulting silica is polycondensed by adding a base to an SiO₂ gel, the water is removed from the gel obtained by extractive distillation with an organic solvent which is mixed with water on cooling forms a two-phase azeotrope, reacting the gel with a silylating agent, and then drying at pressures and temperatures below the critical pressure and / or the critical temperature of the organic solvent used in the water removal. |