Applications of Silicas

(2003) Paint Coat. Ind., Defining and Predicting Performance of Surface Modifiers in Coatings, 19 (10), 110, accessed atwww.pcimag.com. SpecialChem. SA. (2003) Additives for tribological polymers used in bearing applications, article accessed at www. specialchem4polymers.com/resources/ articles. 

TribolCogy-abc, Solid lubricants/dry lubrication at www.tribology-abc.com/ abc/solidlub.htm. 

GE Advanced Ceramics, Lubrication at www.advceramics.com/geac/ applications /lubrication/. 

National Institute for Occupational Safety and Health (US NIOSH), Molybdeniun sulfide at www.cdc.gov/niosh/rtecs/ qa47aba8.htinl. 

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ANALYTICAL APPLICATION OF SILICAS WITH COVALENT AND ION-EXCHANGE BONDING OF IMMOBILIZED ORGANIC COMPOUNDS FOR SELECTIVE PRE-CONCENTRATION AND DETERMINATION OF PHENOLIC POLLUTANTS... 

Cabrera, K. Applications of silica-based monolithic HPLC columns./. Sep. Sci. 2004, 27, 843-852. 

Bushey, M.M., Jorgenson, J.W. (1990). Automated instrumentation for comprehensive two-dimensional high-performance liquid chromatography of proteins. Anal. Chem. 62,161-167. Cabrera, K. (2004). Applications of silica-based monolithic HPLC columns. J. Sep. Sci. 27, 843-852. 

Walcarius, A. 2001. Electrochemical applications of silica-based organic-inorganic hybrid materials. Chem. Mater. 13 3351-3372. 

Many applications of silica-based nanoporous materials such as adsorption, ion exchange, catalysis and sensing, require specific surface properties. Since the discovery of the MCM series of mesoporous materials [1], two main methods have been used to functionalize their large internal surface [2]. 

Since the first synthesis of mesoporous materials MCM-41 at Mobile Coporation,1 most work carried out in this area has focused on the preparation, characterization and applications of silica-based compounds. Recently, the synthesis of metal oxide-based mesostructured materials has attracted research attention due to their catalytic, electric, magnetic and optical properties.2 5 Although metal sulfides have found widespread applications as semiconductors, electro-optical materials and catalysts, to just name a few, only a few attempts have been reported on the synthesis of metal sulfide-based mesostructured materials. Thus far, mesostructured tin sulfides have proven to be most synthetically accessible in aqueous solution at ambient temperatures.6-7 Physical property studies showed that such materials may have potential to be used as semiconducting liquid crystals in electro-optical displays and chemical sensing applications. In addition, mesostructured thiogermanates8-10 and zinc sulfide with textured mesoporosity after surfactant removal11 have been prepared under hydrothermal conditions. 

This property is responsible for the fact that silica gels are mainly applied for adsorption while fumed silicas are used in rheological applications. In these the presence of highly dispersed small particles is important. The applications of silica will be discussed in detail furtheron. 

The CSC precursor build-up has been studied after modification of the silica gel surface from the gas phase. This gas phase modification involves the deposition of one molecular layer at the time. For thicker coatings, a cyclic procedure is needed. Liquid phase modification of the silica surface may also yield valuable ceramic precursors. The precursor molecular structure and layer thickness is controlled by other parameters compared to gas phase procedures. Parameters such as reaction solvent, silane concentrations and presence of water are of primal importance. Those have been discussed in detail in chapter 9. In this chapter, the application of silica modified with aminosilanes, will be discussed. The aminopropylsilica is used as a prototype compound for the production of ceramics by liquid phase chemical surface coating. 

Many reviews have been written on the preparation, physico-chemical properties and application of silica in modem separation science [5-7]. RP LC with silica based bonded stationary phases is utilised for the majority of LC separations in laboratories world-wide. Their ubiquity derives from their versatility, in that generally a wide range of both ionic and non-ionic analyte species can be separated with these columns by careful selection of the stationary phase and mobile phase properties. 

In the case of H20, CO, and N20, experimental evidence has demonstrated that the principal interaction mechanism is also H bonding of Si-OH, to the C end of CO, to the O end of N20, and to the O atom in, H20 [124], Because of these properties, silica gel could serve as an excellent adsorbent for water vapor and pollution gases. Particularly, zeolites and silica gels are the adsorbents mainly applied today as dryers [129], An additional application of silica is hydrogen sulfide and carbon dioxide adsorptions [130,131],... 

Medical Chemistry and Clinical Application of Silica, edited by A. A. Chuiko (Naukova Dutnka, Kiev, 2003). 

Lohray and coworkers reported the first application of silica gel-supported Cinchona alkaloids in AD in 1996 [67], A 3,6-DHQ2-pyridazine derivative was linked to a silica gel support with an attachment point at one of the quinudidine moieties (Fig. 4, catalyst 13). The alkaloidic ligand was expected to bind to the silica surface resulting in better availability of the active site compared to polymer-... 

Researchers turned their attention to applications of silica gel as a new electrode material. Silica gel, which has a three-dimensional structure with high specific surface area and is electroinactive in an aqueous medimn can be used as a support for electroactive species during their formation and/or enzymes by adsorption or entrapment [92,93]. Patel et al. recently reported application of poljwinyl ferrocene immobilized on silica gel particles to construct glucose sensors. Efficiency of carbon paste electrodes prepared with these polymeric electron mediators and GOx was comparable to electrodes constructed with other ferrocene based polymeric electron transfer systems. The fact that 70% of initial anodic current was retained after a month when electrodes were kept in the buffer at room temperature shows that polymerization of monomer vinylferrocene in the pores of silica gel and entrapping GOx in the matrix of poljwinyl ferrocene appears to have added stability to the sensors [94]. 

The most popular reversed-phase columns are manufactured from silica-based bonded phases, and, among those, the Cig-type bonded phase is most frequently used. These bonded phases are prepared by reacting silica with a reactive silane that carries the hydrophobic ligand after which the phase is named. However, the poor stability of silica at extreme pH values, along with the presence of underivatized silanol groups that most frequently cause secondary interactions, limits the application of silica-based supports in liquid chromatography. 

Thin-layer chromatographic silica gels have specihc pore volumes ranging from 0.5 to 2.0 mL/g sorbents with the highest values are preferred for partition chromatography. Typical applications of silica gel in TLC separation of classes of organic compounds are listed in Table 2. 

Due to the extensive experience gained in analysis of alkaloids by TLC on silica gel plates and. the initial poor peak performance of basic compounds in reversed-phase HPLC, the number of applications of silica gel as stationary phase in the HPLC of alkaloids is relatively high, as compared with other groups of compounds. 

However, under basic conditions the stability of silica gel is poor18. Depending on the nature of the organic solvents used 1n combination with the basic modifier, the silica gel is dissolved at various rates. This limits the applicability of silica gel as stationary phase in the HPLC analysis of alkaloids. For certain solvent systems the column life can... 

Occurrence, synthesis, properties and applications of silica adsorbents are presented. The surface characterization of the materials are described in detail. Same attention was given to the use of pores of silica adsorbents. 

G.H. Beall, Industrial applications of silica, in Silica Physical Behavior, Geochemistry and Materials Applications, Reviews in Mineralogy, Vol. 29, P.J.Heaney, C.T. Prewitt, and G.V. Gibbs (eds.), Mineralogical Society of America, Washington, DC, 1994, pp. 469-505. 

Silica is an oxide with innumerable variations. On the basis of this structural variability, a variety of different types of materials have been prepared, such as compact fused silica, in the form of plates, fibers, or finely dispersed pellets, and porous materials. Because compact silica is mostly used for optical components or applications for which high chemical durability is required, porous and finely dispersed materials have completely different applications, for example, as fillers, adsorptive materials, or strengtheners in composites. Various aspects of the chemistry, physics, and applications of silica are described in detail in the book by Iler (I), with special consideration given to finely dispersed and porous materials. 

Kolosentsev, S. D. Belotserkovsky, G. M. In Preparation and Application of Silica Hydrosols Frolov, Yu. G., Ed. Proceed, of Mendeleev Chemico-Technological Institute Moscow, 1979 Issue 107, p 44. 

The primary application of silica gel is as a drying agent. Packets of silica gel are found in many consumer products, such as electronic equipment, hardware tools, clothing, CD and DVD discs, and foodstuffs. Because of its ability to adsorb moisture from the surrounding air, silica gel prevents rust and other forms of oxidation. Silica gel also has similar applications in industry. For example, it is used to dry compressed air, air conditioning systems, and natural gas. The compound is also used to bleach petroleum oils and as an anti-caking agent for cosmetics and pharmaceuticals. 

These results were the first investigation regarding the relationship between the cytotoxicity of silica and the population doubling time of different cell lines as well as the benefits of using chitosan to prepare composite silica nanoparticles. They would be relevant for future applications of silica nanoparticles in drug delivery and controlled release applications. 

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