Fumed-silica gel

The use of a 7% fumed-silica gel with silica frit bridges of the style shown in Figure 5.6a has been recommended.14 Fumed silica forms stable gels with water and a number of organic solvents, but the aqueous gel is not stable above pH 8. 

These data (2, 80, 83, 84) indicate that skeletal densification at intermediate temperatures is observed in general for metal alkoxide derived silicate xerogels, whereas aqueous silicates have skeletal densities comparable to silica glass, and thus, like the fumed silica gel discussed earlier, exhibit little skeletal densification at intermediate temperatures. 

See also Diatomaceous earth Quartz Silica, amorphous Silica, amorphous hydrated Silica, colloidal Silica, fumed Silica gel Silica, hydrated... 

Jeffrey S. Moore of the University of Illinois prepared J. Org. Chem. 2008, 73, 4256) a Mo alkyne metathesis catalyst on fumed silica gel that converted 28 to 29 at room temperature. The cyclization was driven by the vacuum removal of 3-hex5me 30. In the same paper. Professor Moore used the insolubility of a product diaryl alkyne 31 to drive other cyclizations. 

The above methods for obtaining D, as well as other ones, are reviewed in Refs. 3-12, and Refs. 7-9 give tables of D values for various adsorbents. For example, D is close to 3 for the highly porous silica gels and close to 2 for nonporous fumed silica and for graphitized carbon black coconut charcoal and alumina were found to have D values of 2.67 and 2.79, respectively [7]. 

Paraffin (oil) [8012-95-1 ] d 0.880, n 1.482. Treated with fuming H2SO4, then washed with water and dilute aqueous NaOH, then percolated through activated silica gel. 

Hydrogen chloride [7647-01-0] M 36.5. Passed through cone H2SO4, then over activated charcoal and silica gel. Fumes in moist air. Hydrogen chloride in gas cylinder include ethylene, 1,1-dichloroethane and ethyl chloride. The latter two may be removed by fractionating the HCl through a trap cooled to -112°. Ethylene is difficult to remove. Fumes in moist air. HARMFUL VAPOURS. 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

The nonporous spherical gels for PCHdC are often specially prepared for research purposes. However, nonporous polystyrene/divinylbenzene beads. Solid Bead, can be obtained in various particle sizes from Jordi Associates, Inc. (Bellingham, MA). Columns packed with these gels can be used for HdC of the polymers that are currently analyzed using polystyrene/divinylbenzene SEC columns. Fumed silica nanospheres are offered by Cabot (Tuscola, IL) (17), and nonporous silica (NPS) microspheres are offered by Micra Scientific, Inc. (Northbrook, IL). These nonporous silica gels may also be used for HdC. 

The preparation and properties of a novel, commercially viable Li-ion battery based on a gel electrolyte has recently been disclosed by Bellcore (USA) [124]. The technology has, to date, been licensed to six companies and full commercial production is imminent. The polymer membrane is a copolymer based on PVdF copolymerized with hexafluoropropylene (HFP). HFP helps to decrease the crystallinity of the PVdF component, enhancing its ability to absorb liquid. Optimizing the liquid absorption ability, mechanical strength, and processability requires optimized amorphous/crystalline-phase distribution. The PVdF-HFP membrane can absorb plasticizer up to 200 percent of its original volume, especially when a pore former (fumed silica) is added. The liquid electrolyte is typically a solution of LiPF6 in 2 1 ethylene carbonate dimethyl car-... 

First spray the dried chromatogram homogeneously with reagent 1. Then remove excess reagent in a stream of cold air in the fume cupboard (ca. 30 min for silica gel and 3 h for aluminium oxide layers). Then spray the chromatogram lightly with reagent 2. 

Silica is the support of choice for catalysts used in processes operated at relatively low temperatures (below about 300 °C), such as hydrogenations, polymerizations or some oxidations. Its properties, such as pore size, particle size and surface area are easy to adjust to meet the specific requirements of particular applications. Compared with alumina, silica possesses lower thermal stability, and its propensity to form volatile hydroxides in steam at elevated temperatures also limits its applicability as a support. Most silica supports are made by one of two different preparation routes sol-gel precipitation to produce silica xerogels and flame hydrolysis to give so-called fumed silica. 

Cu/MgO and Cu/Si02 gel were found to be the most active, followed by the catalysts obtained supporting copper on fumed silica and silica modified with small amount of a second oxide containing Lewis acid sites. It is also worth noting that the reaction over Cu/MgO is selective while small amounts of secondary products are formed over the other catalysts. 

Bartholomew and coworkers32 described deactivation of cobalt catalysts supported on fumed silica and on silica gel. Rapid deactivation was linked with high conversions, and the activity was not recovered by oxidation and re-reduction of the catalysts, indicating that carbon deposition was not responsible for the loss of activity. Based on characterization of catalysts used in the FTS and steam-treated catalysts and supports the authors propose that the deactivation is due to support sintering in steam (loss of surface area and increased pore diameter) as well as loss of cobalt metal surface area. The mechanism of the latter is suggested to be due to the formation of cobalt silicates or encapsulation of the cobalt metal by the collapsing support. 

The synthesis of SSZ-26 (24) involved combining 76 g of a 0.45 M solution of 2 with 158 g of NaOH. Then, 0.9 g of sodium aluminate were added followed by 9.1 g of fumed silica. The gel was heated at 175°C for 6 days with stirring at 60 rpm. A Y type zeolite has also been successfully used as the source for aluminum in the recipe. Note that the methyl groups in SSZ-26 template 2 could point up or down relative to the cyclohexyl ring but as it turns out both isomers make this phase. 

Surface Sol-Gel Modification of Fumed Silica with Ti02/Al20s orAfO / T1O2 Double Layer. The basic procedure for functionalization of Cab-O-Sil silica... 

Physical Form. Fine white powder with particle sizes generally below Ipm. This is not the same as the commercial products fumes silica, silica gel, precipitated silica, or fused silica. It is formed during the electric arc production of elemental silicon from... 

Amorphous Silica The term amorphous silica refers to aggregate of smaU particles with high specific surface area. They lack crystal structure and do not form a sharp x-ray diffraction pattern. They are known in several forms such as colloidal silica, precipitated silica, silica gels, and fumed sdica. The surface of such amorphous silica may contain silanol (SiOH) groups or can be anhydrous. 

Silicone polymers when cured into elastomers by themselves are weak, gel-like materials. For this reason, fillers must be used to provide reinforcement. The type of fillers (qv) used in silicone sealants varies widely two of the most common fillers are fumed silica and calcium carbonate. 

Silica and Unimin Corporation. Alternatives to the natural quartz powder, including fumed silica, flame-hydrolyzed soot, and sol—gel-derived powder, have also been tried as feedstock for these processes (11). 

---