Fumed silicas production

Barthel, H., Rosch, L., and Weis, J., Fumed Silica-Production, Properties, and Applications, in Organo-silicon Chemistry II From Molecules to Materials, VCH Weinheim, Germany, 1996 Vol. II, 761. 

Obviously, aU data points in the range of qRg,es = 1—4- lie essentially on one curve. That means that all aggregates of the examined fumed silica product belong to the same class of aggregates and obey approximately a universal scattering behaviour. The experimental correlation of Fig. 4.25 can be approximated for qRg es - 4 with the following equation ... 

In particular, fumed alumina and fumed silica products provide tribo-charging, free-flow, fluidization and anti-blocking in powder coating applications. Typically, fumed alumina is used for tribo coating processes and either fumed silica or hexamethyldisilazane treated fumed alumina is selected for corona coating processes (3). 

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 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-... 

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. 

According to the Illinois Environmental Protection Agency (IEPA), a series of gas blowouts has occurred at two waste injection wells in the state (Brower el al., 1989). In each case, well operators were injecting concentrated hydrochloric acid into a dolomite bed. At its plant near Tuscola, the Cabot Corporation injects acid waste from the production of fumed silica into the Cambrian Eminence and Potosi Formations below 5 000 ft (1 500 m) depth. Allied Chemical Corporation injects acid into the Potosi formation below about 3 600 ft (1 100 m). The acid, which is contaminated with arsenic, is a byproduct of the manufacture of refrigerant gas. Since some of the blowouts have caused damage such as fish kills, there is environmental interest as well as operational concern in preventing such accidents. 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

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... 

A 75% ferrosilicon furnace operating at 90% silicon recovery would give 0.24 kg of by-product silica fume per kg of silicon produced. A silicon metal furnace operating at 85% recovery (typical of the industry) would give 0.38 kg of fume silica per kg silicon produced. 

The hand lay-up or spray-up process, used universally for the production of laminar composites incorporating glass fiber reinforcement, is most efficient for the manufacture of large parts, such as boats, bathtubs, tanks, architectural shapes, and recreational accessories. Resins intended for spray-up processes are usually modified with thixotropic additives, such as fumed silica (1%), to reduce the risk of drainage when applied over large vertical mold surfaces. Molds are also made from FRP for short-run products usually surfaced with a tooling gel coat to provide consistent surface quality and appearance. 

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