Sodium Silicate Silica Gel

Soda ash is heated with sand at 1200-1400°C to form various sodium silicates (over 40 of them), which collectively are produced at levels sufficient to rank in the top 50. Some common ones are listed here. 

Thompson, Industrial Inorganic Chemicals Production and Uses, pp. 123-148. 

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Sodium silicate (silica gel, water glass) is produced when sodium carbonate (soda ash, NajCC ) is heated with sand at 1200 to 1400°C to form various forms of sodium silicate (Fig. 1). 

In this procedure the soil sample (spiked with isotopic marker compounds) is processed in a two-part enrichment procedure (Fig. 5.3). In part I, a mixture of the sample and sodium sulphate is subject to solvent extraction, and the extract is, in the same process, passed through a series of silica-based adsorbents and then through the carbon/glass fibre adsorbent. The extract passes through the adsorbents in the following order potassium silicate, silica gel, cesium or potassium silicate, silica gel and finally an activated-carbon... 

Silica gel can be made by reacting an acid with sodium silicate, which is sold in drug stores as water glass or egg keep, and is used to paint eggs to seal them from air and prevent spoilage. Drying the resulting gel will get the desiccant, or it can be used wet in toothpastes. 

Silica gel is prepared in two stages. Firstly, an intimate mixture of sand and sodium carbonate are heated together in iron pans forming sodium silicate with the release of carbon dioxide. The sodium silicate is leached out of the cooled mixture, unreacted sand removed by filtration, and the resulting silicate solution treated with hydrochloric or sulfuric acid. 

A solution of sodium methoxide (80 mmol) in methanol (40 mL) is added to silica gel (2.7 g, 45 mmol) followed by a solution of catechol (13.2 g, 120 mmol) in methanol (40 mL). The resulting mixture is stirred and heated under reflux for 18 h. The methanol is then evaporated and the solid residue washed with ether. The black sohd is dissolved in THF (400 mL) and the resulting solution is heated for 1 h in the presence of charcoal. After filtration and evaporation of the solvent the sodium tris(benzene-l,2-diolato)silicate 80 is isolated as a white powder (12.53 g, 70% Scheme 2.20) [93]. 

Even though silicon is extremely abundant, only one silicon-containing compound appears in the list of top 50 industrial chemicals. That is sodium silicate, Na2 Si03, used for the manufacture of silica gel and glass. Nevertheless, with the advent of the electronic age silicon has become an extremely important substance that is the primary ingredient of most semiconductors. Because these are microscale devices, the quantity of production of silicon remains small compared with that of fertilizers and construction materials. Although relatively small in quantity, the value of silicon products is quite high. 

Prepared from sodium silicate using the sol-gel procedure. Silica gel is the most widely used general purpose adsorbent for sample cleanup although it may irreversibly bind some strongly basic substances. Generally considered to be slightly acidic in character but this may vary with the method of prq ration. Activated by heating at about 180 C for 8-12 hours. 

Silica gel. Silica gel is a porous amorphous form of silica (Si02) and is manufactured by acid treatment of sodium silicate solution and then dried. The silica gel surface has an affinity for water and organic material. It is primarily used to dehydrate gases and liquids. 

Silica gel A regenerative absorbent consisting of the amorphous silica manufactured by the action of HCI on sodium silicate. Hard, glossy, quartz-like in appearance. Used in... 

The higher intensities /3 measured for ion exchanged gels (gels prepared by procedure b) comparing to /3 of gels prepared by procedure a, are probably the result of the different silica source used. It was found that gels prepared from sodium silicate contain... 

Urokinase utilized medically is generally purified directly from human urine. It binds to a range of adsorbents, such as silica gel and, especially, kaolin (hydrated aluminium silicate), which can be used initially to concentrate and partially purify the product. It may also be concentrated and partially purified by precipitation using sodium chloride, ammonium sulfate or ethanol as precipi-tants. 

Silica gel is a three-dimensional polymer of silicic acid, usually synthesized from tetrachlorosilane or sodium silicic acid. The reaction is as follows ... 

By achieving random dispersion of the Kaolin in the sodium silicate solution prior to formation of the silica-alumina gel, it was possible to disperse the clay crystals. They condensed somewhat perpendicular to each other and were bound together by silica-alumina gel. I therefore speculated that spray drying, during which the gel system contracts, might create a dual structure. An analogy would be a house built of cards (Kaolin), cemented together with silica-alumina gel. 

Precipitated silicas are also produced by the addition of sulphuric acid to a solution of sodium silicate but under different conditions, which result in the formation of aggregates of tiny discrete particles rather than the massive structure of a gel. After precipitation the slurry is filtered, washed, dried and deagglomer-ated. 

Silica gel is synthetic amorphous silica consisting of a compact network of spherical colloidal silica particles. Its surface area is typically between 300 and 850 m2/g. The predominant pore diameters are in the range 22-150 A. Silica gel is produced via the following procedure a sodium silicate solution reacts with a mineral acid, such as sulfuric acid, producing a concentrated dispersion of finely divided particles of hydrated Si02,... 

Hydrothermal synthesis of the non-uniform silica gel used for preparative chromatography proceeds in a different fashion. Sodium silicate (IMa2Si03),1 obtained by alkaline fusion of very pure sand, is acidified to yield orthosilicic acid (Si(0H)4). This unstable acid initially dimerises then condenses further to yield a gel with a hydroxylated surface. Under conditions of controlled polymerisation, a hydrogel is obtained which is further calcinated to yield a very dense silica gel (xerogel). Some of the processes involved here are of the same type as those used to produce microspheres for analytical chromatography. 

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