| 摘要 |
Sols and gels are prepared by treating an aqueous solution of a sodium or potassium siliconate with a solution of an acid in a water-miscible organic solvent, the final pH value being 7 or less if a sol is required and above 7 if a gel is required, and there being in the latter case at least 15 per cent of the solvent present. If the acid forms with the metal ion a salt insoluble in the solvent mixture, and the precipitated salt is removed, a sol of greater stability is obtained. There are specified: siliconates-sodium methyl, sodium ethyl and potassium methyl siliconates; acids-acetic and sulphuric; solvents-ethyl and isopropyl alcohols and acetone. In examples: (1) aqueous sodium methyl siliconate solution is run into a solution of acetic acid in 95 per cent alcohol to give a stable sol at pH 6.2; (2) aqueous sodium methyl siliconate solution is run into a solution of sulphuric acid in 95 per cent alcohol, precipitated sodium sulphate is filtered off, and a stable sol at pH 1.5 obtained; (3) aqueous sodium ethyl siliconate solution is run into alcoholic acetic acid solution to obtain a stable sol at pH 6.1; (4) aqueous sodium methyl siliconate solution is run into a solution of sulphuric acid in 33 per cent aqueous alcohol to a pH of 6.5, further 95 per cent alcohol was added (raising the pH to 7.2), the precipitated sodium sulphate removed and a sol obtained which after 48 hours gelled; part was dried to an aerogel and part extracted with ether and dried above the critical temperature and pressure as explained in Specification 607,427 to a water-repellent aerogel; (5) a mixture of methyl trichlorosilane and dimethyl dichlorosilane is hydrolysed in ice water and the precipitate dissolved in alcoholic sodium hydroxide; the solution is run into aqueous alcoholic sulphuric acid to produce a sol of pH 6.2 to which further alcohol was added, followed by removal of precipitated sodium suphate; (6) alcoholic acetic acid is added to a mixture of alcoholic potassium methyl siliconate and aqueous sodium methyl siliconate to give a sol of pH 7.4 which rapidly gelled.
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