Silical silica gel

C (associated with various transition metals) Si Si02 (associated with Ti02) Aluminium silicate Silica gel as support or alone 1,2-Ethanediol Various alcohols and acids Various alcohols and acids Various alcohols and acids Terephthalic 129,130) 51,70) 124) 36,131, 134-137, 175)... 

Figure 6. Raman spectra of silicates silica gel dried at 50°C, heated to 600°C, consolidated at 1100°C, and conventionally prepared fused silica.

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... 

Human adipose tissue (CDDs) Clean-up of sample on potassium silicate/silica gel column, elution with cyclohexane/CH2CI2 clean-up on carbon column, elution with toluene clean-up sequentially on potassium silicate column in tandem with alumina column, elution with hexane followed by CH2CI2 in hexane HRGC/HRMS (EI/MIM) No data No data Nygren et al. 1988... 

Incinerator stack emission air from contaminated building (CDDs) Addition of 13C-labeled TCDD to collection tube followed by collection of sample addition of internal standards Soxhlet extraction clean-up and sequential fractionation on acidic silica/potassium, silicate/silica gel, acidic alumina, carbon, neutral alumina columns volume HRGC/HRMS (MIM) 1 pg/m3 No data Smith et al. 1986b... 

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). 

Si02 Na. Lower concentrations of silicate are used in silica gel preparation. In the absence of a coagulant, silica is not precipitated from solution at any pH... 

Silika-gel, n. silica gel. -stein, m. silica brick. Silikat, n. silicate. -emaUle, /. sUicate enamel. 

Thin-layer plates were made with silica gel-calcium sulfate and each contained a mixture of zinc silicate and zinc cadmium sulfide as phosphors. Separated components are generally visible under ultraviolet light by fluorescence quenching. This was true, in part, for the pyrethrins, except that some of the separated components possessed a natural fluorescence under the ultraviolet lamps. 

Silicic acid silica gel amorphous silicon dioxide... 

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. 

As a result of its unique chemical and physical properties, silica gel is probably the most important single substance involved in liquid chromatography today. Without silica gel, it is doubtful whether HPLC could have evolved at all. Silica gel is an amorphous, highly porous, partially hydrated form of silica which is a substance made from the two most abundant elements in the earth s crust, silicon and oxygen. Silica, from which silica gel is manufactured, occurs naturally, either in conjunction with metal oxides in the form of silicates, such as clay or shale, or as free silica in the form of quartz, cristobalite or tridymite crystals. Quartz is sometimes found clear and colorless, but more often in an opaque form, frequently colored... 

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. 

However, the free acid quickly starts to condense with itself, accompanied by the elimination of water to form dimers, trimers and eventually polymeric silicic acid. The polymer continues to grow, initially forming polymer aggregates and then polymer spheres, a few Angstroms in diameter. These polymeric spheres are termed the primary particles of silica gel and must not to be confused with the macro-particles of silica gel that are packed into the LC column. 

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. 

Sheet silicates (Q ) with significant isomorphic replacement of Si by AF+ or Fe +. These were decomposed by poly(acrylic add) to silica gel. The chlorite, thuringite, formed a strong cement but was much affected by water. 

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