Acid gel formation

In silicic acid gel formation, a considerable increase in volume is observed, starting directly after the acidification of the sodium silicate solution and before the solution has set to a gel. It also continues for a long time after setting. The volume increase here obviously runs parallel with the polymerisation of the silicic acid, a reaction involving the formation of water which was formerly chemically bound by the silicic acid. A dilatation is always observed in such condensation reactions. 

Alkoxide precursors, hydrolysis with acetic acid, gel formation overnight [100]... 

Silicate Grouts. Sodium silicate [1344-09-8] h.3.s been most commonly used in the United States. Its properties include specific gravity, 1.40 viscosity, 206 mPa-s(=cP) at 20°C Si02 Na20 = 3.22. Reaction of sodium silicate solutions with acids, polyvalent cations, such organic compounds as formamide, or their mixtures, can lead to gel formation at rates, which depend on the quantity of acid or other reagent(s) used. 

During studies on the acid-induced formation of the alkaloid yuehchukene and related structures from pienylindoles, it was discovered that treatment of indole 173 with p-toluenesulfonic acid and silica gel leads to the formation of indolo-[3,2-b]carbazole 174 and the indole derivative 175 (Scheme 21). Similarly, the disubstituted product 176 could be isolated after TFA treatment of the substrate 177. Detailed mechanistic explanations have also been provided in this work (96T9455). 

Guo et al. [70,71,73] recently attempted to hydrogenate NBR in emulsion form using Ru-PCy complexes. However, successful hydrogenation can only be obtained when the emulsion is dissolved in a ketone solvent (2-butanone). A variety of Ru-phosphine complexes have been studied. Crosslinking of the polymer could not be avoided during the reaction. The use of carboxylic acids or first row transition metal salts as additives minimized the gel formation. The reactions under these conditions require a very high catalyst concentration for a desirable rate of hydrogenation. 

An advanced solution to the problem of decreasing the free mobility of the electrolyte in sealed batteries is its gel formation. By adding some 5-8 wt.% of pyrogenic silica to the electrolyte, a gel structure is formed due to the immense surface area (-200-300 m2 g ) of such silicas, which fixes the sulfuric acid solution molecules by van der Waals bonds within a lattice. These gels have thixotropic properties i.e., by mechanical stirring they can be liquefied and used to Filled into the... 

A simple example of gel formation is provided by chitosan tripolyphosphate and chitosan polyphosphate gel beads the pH-responsive swelling abihty, drug-release characteristics, and morphology of the gel bead depend on polyelectrolyte complexation mechanism and the molecular weight. The chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution by ionotropic cross-hnking or interpolymer complexation, respectively. 

Polymers of acrylic acid and methacrylic acid have been tested for their gel-formation ability [1396]. They are used with gel-forming additives similar to those described for polyacrylamides. Also, mixtures of latex with methacrylate-methacrylic acid copolymer as an additive have been described as plugging agents [1041]. 

Fig. 8. Gel formation of peroxide crosslinked poly(HAMCL), based on coconut fatty acids (COFA), oleic acid (OA), tall oil fatty acids (TOFA) or linseed oil fatty acids (LOFA)...

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