Disilicic acid

Disilicic acid [(H0)3Si]20 has been the subject of numerous investigations (201,202). At the 6-31G level of theory with polarization functions on the bridging oxygen, the Si-O(bridging) length is 1.617 A and the Si-O-Si angle 141° (203). 

SILICIC. 1. Containing or pertaining to silicon. 2. Containing silicic acid (ortho) HrSiOa or silicic acid (meta) HiSiC or silicic acids of a higher degree of hydration (disilicic acids, trisilicic acids, etc.). 

III. A POTENTIAL ENERGY SURFACE FOR THE Si-O-Si SKELETON OF THE DISILICIC ACID MOLECULE... 

Two molecules of Disilicic acid. 1st anhydride, orthosilicic acid. 

H0B4O7, tetraboric acid (HBOo)n, metaboric acid (u S) H3SLO7, disilicic acid... 

In alkaline solutions, silica exists in the form of silicate ions e.g., Si03 ). In dilute solutions (up to 0.1 mg of Si per ml) between pH 1 and 8, water-soluble monomeric silicic acid is the stable form. In more concentrated solutions of the same acidity, monosilicic acid condenses to disilicic acid and polysilicic acids which can be transformed into colloidal species. 

The yield depends solely on the degree to which moisture is excluded and on the water content of the alcohol. If, for example, 96% alcohol is used instead of absolute alcohol, the principal product will be esters of disilicic acid and polymeric metasilicic acid. Esters of other alcohols can be obtained in the same manner in the preparation of the methyl ester, however, special care must be taken to exclude moisture, and perfectly dry methanol must be used. 

A particular example of a macromolecular gel is the silicic acid gel, which is formed from sodium silicate solutions upon acidification. According to WiLLSTaxTER et aL mono or disilicic acids are formed in the reaction, which undergo polymerisation giving rise to high molecular silicic adds Since the polymerisation is a 3-dimensional one, a molecular framework is built. Polymerisation continues long after the solution has set to a gel. The case is comparable to that of the polymerisation of phenolformalde-hyde solutions setting to a gel (cf. Ch. II, p. 39). 

Figure S Two-tetrahedral models used to derive CFF parameters for zeolites disilicic acid (top) and aluminum-disilicic add (bottom). The models are terminated with...

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