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The history of the sol-gel method can be traced back to the middle of the 19th century. Ebelman found that the hydrolysis of ethyl orthosilicate formed silicon dioxide glassy. Graham found that the water in the silicon dioxide gel could be replaced by an organic solvent. This phenomenon caused the chemist Of the attention. In the 1930s to 70s mineralogists, ceramic scientists, glass scientists were prepared by sol-gel phase diagram of homogeneous samples, and at low temperatures to prepare a transparent ceramic and heat-resistant glass , This stage from the application of colloidal chemistry to the preparation of inorganic materials to obtain initial success, has aroused people's attention. In addition, the method is controlled at the beginning of the preparation of the material, so that the uniformity can reach sub-micron level, nanometer level or even molecular level, and then realize that this method can be used to cut the performance of materials. The sol-gel method can be used not only to prepare fine powders, but also to prepare films, fibers, bulk materials and composites.

Hydrolysis of metal alkoxide is usually a metal alkoxide as raw material, through hydrolysis and polycondensation reaction system in the sol. More specifically, silicon alkoxide or silicon halide as raw material, alcohol as co-solvent, as a catalyst by adding acid or alkali solution, by silicon alkoxide or silicon halide hydrolysis, polycondensation, the formation of silicon dioxide gel. Finally, washing, drying and calcining are carried out to obtain SiO2 powder. The time for gelation depends on pH, temperature, amount of water added and the nature of the catalyst. Usually divided into one-step sol-gel method and two-step sol-gel method.

Compared with other methods, the sol-gel method for prepare silicon dioxide has many advantages: (1) the lower reaction temperature, generally room temperature or slightly higher temperature, the majority of organic activity Molecules can be introduced into the system and maintain its physical properties and chemical properties; ② reaction time from the solution, the proportion of each component is easy to be controlled, and to the molecular level of uniformity; ③ does not involve high-temperature reaction, to avoid the introduction of impurities , Can guarantee the purity of the final product; ④ according to need, at different stages of the reaction, preparation of film, fiber or block and other functional materials.


 

 

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