Process for the preparation of xerogels
AssigneeHoechst Aktiengesellschaft
InventorsRolf-Michael Jansen, Andreas Zimmermann
Life of this patent
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Abstract
The invention relates to modified SiO.sub.2 gels (xerogels), the preparation thereof 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 SiO.sub.2 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.
Claims10
A process for the preparation of xerogels, which comprises
- a) adjusting an aqueous waterglass solution to a pH.ltoreq.3.0, using an acid ion exchange resin or a mineral acid,
- b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO.sub.2 gel
- c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is .ltoreq.5% by weight,
- d) reacting the gel obtained in step c) with a silylating agent,
- e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
A process for the preparation of xerogels, which comprises
- a) adjusting an aqueous waterglass solution to a pH .ltoreq.3.0, using a mineral acid, b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO.sub.2 gel,
- c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is .ltoreq.5% by weight,
- d) reacting the gel obtained in step c) with a silylating agent,
- e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
A process for the preparation of xerogels, which comprises
- a) adjusting an aqueous waterglass solution to a pH .ltoreq.3.0, using a mineral acid,
- b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO.sub.2 gel and washing the gel with water until free of electrolytes,
- c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is .ltoreq.5% by weight,
- d) reacting the gel obtained in step c) with a silylating agent,
- e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
Dependencies are inferred from the claim text.