Silica chemical

Fig. 3.1b lists some of the properties of two commercially available microparticulate packings. The first is a 5 /im unmodified silica, the second a 3 fim silica, chemically modified with octadecylsilane (ODS, C-18). 

Fowler, C.E., Khushlani, D. and Mann, S. (2001) Interfacial synthesis of hollow microspheres of mesostructured silica. Chemical Communications, 2028-2029. 

Cobalt Co(III) adsorbed on 8-quinolol adsorbed on silica Chemical luminescence - [244]... 

Transparent vitreous silica chemical durability of, 22 417 density of, 22 422 devitrification of, 22 421 manufacture of, 22 412-415 viscosity of, 22 424t Transpeptidases, 3 27 Transport. See also Transportation of ascorbic acid, 25 771 of hydrated lime, 15 56-57 of quicklime, 15 56 of radioactive waste, 25 855-856 in waste collection, 25 869-870 Transportation, 25 322-348. See also Shipping Transport aluminum applications, 2 340-341 cost of, 25 323... 

C-18 Novapak (Waters) or equivalent, packed with silica, chemically bonded with octadecyldimethylsilyl groups. 

Molecular hydrogen is one of the few compounds that can be introduced into the bulk of vitreous silica. Chemical processes with the participation of molecular hydrogen are used for modifying the structure of this widely used material. The defects of vitreous silica play an important role in these processes. The exposure of =Si-N -H radicals to an atmosphere of H2 at room temperature is accompanied by the chemisorptions of the gas in an amount that is comparable with the number of radicals and by the disappearance of the EPR spectrum of these radicals (radiospectroscopic measurements were performed at 77 K (see Section 12.1)). When diamagnetic centers of the silylene type ((=Si-0)2Si ) also occurred on the sample surface in addition to the PC =Si-N -H, the decay of radicals in an atmosphere of H2 was accompanied by the quantitative formation of new PCs >Si -H. The appearance of the > Si -H radicals in the system suggests that H atoms... 

Figure 1 Active sites on silica chemically modified with aluminium chloride...

HPLC is performed on analytical columns packed with a commercially available solid phase containing long hydrocarbon chains (e.g. Cg, Cig) chemically bound onto silica. Chemicals injected onto such a column move along at different rates because of the different degrees of partitioning between the mobile aqueous phase and the stationary hydrocarbon phase. The HPLC method is not applicable to strong acids and bases, metals complexes, surface-active materials, or substances that react with the eluent. The HPLC method is applicable when the log Kow value falls within the range 0 to 6 (OECD 117, 1989). The HPLC method is less sensitive to the presence of impurities in the test compound compared to the shake-flask method. 

The Diagenesis of Biogenic Silica Chemical Transformations Occurring in the Water Column, Seabed, and Crust... 

Ono, Y., Nakashima, K., Sano, M, Kanekiyo, Y., Inoue, K., Hojo, J. and Shinkai, S., 1998, Organic gels are useful as a template for the preparation of hollow fiber silica. Chemical Communications, 1998 1477-1478. 

The pH value of the reaction mixture shows a relation to the condensation rate the higher the pH value, the faster the condensation reaction. Of course, this relation is well known from simpler silica chemical systems. It thus appears that polyamines do not directly influence the first steps of the condensation reaction, for example by catalytic action or by coordinative interaction between the amine and the silicic acid anions, but that the accelerating effect the polyamines exert is related to the increase of the pH value, i.e. to their basicity. As the molybdate method probes only the first steps of the condensation reaction, significant interactions may, however, occur between larger silicate species and the amines. 

Depending on the surface modification reversed phase silicas can be grouped into (a) monomeric reversed phase silicas chemically modified with monofunctional silanes and (b) polymeric reversed phase silicas with a polymeric layer made by surface reaction with trifunctional silanes. 

Preconcentration of As(III) diethyldithiocarbamate on silica chemically modified with hexadecyl groups was examined [1]. Emulsion liquid membrane (made up of L113A surfactant, liquid paraffin as stabilizer and kerosene as solvent with HCl and KOH as external and internal phases) separation of As(III) and As(V) was applied prior to detection with silver diethyldithiocarbamate ( =510 nm) [2]. The method was applied to Cu ore and slagged ash. 

Attempts to use spectrophotometry for investigation of the oxidation states and forms of Ru(IV) in hydrochloric acid solutions were described [3]. Silica chemically modified with thiourea derivatives was used to determine Os in the slime of wet dust collection and in wash acid [4]. 

Figure 4.3 Supported metal complexes based on silicas chemically modified with a double imine...

Silica chemically modified with salicylimine will effectively complex metal ions. The heterogeneous metal complexes show some activity in the oxidation of cyclohexane and in alkylaromatics.66... 

K.G. Proctor, S.K. Ramirez, K.L. McWilliams, J.L. Huerta, and J.J. Kirkland, The Progressive Effect of Surface Silylation on the Silanol Population of Silica, Chemically Modified Surfaces, J.J. Pesek, M.T. Matyska and R.R. Abuelafiya, Eds., Royal Society of Chemistry, Cambridge, UK, pp. 45-60, 1996. 

The starting sol must first of all be a dispersion of amorphous silica ultimate particles. Since the silica in the ultimate product is to be amorphous it is highly important that the sihca particles in the starting sol be free of crystallinity. Methods for determing the presence of crystallinity by x-ray techniques are discussed in R.B. Sosman s The Properties of Silica, Chemical Catalog Company, Inc., New York, 1927, page 207. 

Typical adsorbents for SPE are silica, chemically modified with a Cig alkyl chain, commonly referred to as Ci8 highly cross-linked pol) tyrene-divinylbenzene copol)nners (PS-DVB), commonly referred to as PRP-I, Envichrom P, Lichrolut, RP-102, N-vinyl-pyrro-lidone polymer commordy referred to Oasis, and GCBs, commonly referred to as Carbo-pack, Envicarb, Carbograph 1, and Carbograph 4. All these materials are commercially... 

There are many different ways to combine the three main ingredients (metallocene molecule(s), MAO, and the silica) chemically to obtain the final supported metallocene catalysts. One of the most recommended procedures in the patent literature is to first treat the silica with MAO and then combine it with metallocene molecules. No matter which procedure is used, one must be aware that the resulting final heterogeneous metallocene catalyst is very reactive towards moisture, leading to its destruction, and to polar molecules that act as a very effective poison and deactivate the catalyst in an irreversible manner. The long-term storage of different batches of supported catalyst under inert atmosphere, in a temperate environment that excludes excessive heat, and with no exposure to light is essential for its constant activity and reliability. 

Schilde, C., Gothsch, T., Quarch, K., Kind, M., and Kwade, A. (2009) Effect of important precipitation process parameters on the redispersion process and the micromechanical properties of precipitated silica. Chemical Engineering ei Technology, 32 (7), 1078—1087. 

Composites used in Dentistry were developed in 1962 by combining dimethacrylates (epoxy resin and methacrylic acid) with silanized quartz powder [49]. Modem restorative composites are comprised of synthetic monomers, typically dimethacrylates, reinforcing fillers, typically made from radiopaque glass, quartz or silica, chemicals which promote or modify the polymerization reaction, and silane coupling agents which bond the reinforcing fillers to the polymer matrix [26]. 

Sorbents are particulate materials such as silica, chemically-modified silica, alumina and organic resins that can interact with and retain substances from solutions. Retained substances can be subsequently released back into a suitable solvent under controlled conditions. 

Stationary phase (pacidng) Porous, microparticulate silica, chemically-modified silica (bonded phases) or styrene/divinyl benzene co-polymers Stationary phase (pacidng) Porous, microparticulate silica, chemically-modified silica (bonded phases) or styrene/divinyl benzene co-polymers... 

Naik, R.R., Tomczak, M.M., Luckarift, H.R., Spain, J.C. and Stone, M.O. (2004) Entrapment of enzymes and nanoparticles using biomimetically synthesized silica. Chemical Communications, 1684-5. 

Z, Li, W, and Wang, Y. (2006) Mesostructured silica chemically doped with Ru-n as a superior optical oxygen sensor. Adv, Funct, Mater., 16, 1883-1891. 

When levels are being considered as a means of control, it must always be borne in mind that quantitative analysis must be accompanied by qualitative findings as well. Apart from the standard microscopical checks for ferrous and ferric oxides, aluminium and silica, chemical analyses are used to establish acid and water levels in the carrier fluid. If this is insufficient, the analysis is then extended to one or more of the following techniques ... 

G. Berrod, A. Vidal, E. Papirer, J. B. Donnet. Reinforcement of siloxane elastomers by silica. Chemical interactions between an oligomer of poly(dimethylsiloxane) and a fumed silica. /. Appl. Polym. Sci., 26,833-845,1981. 

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