Synthetic silica silicates

Many catalysts have been used but the standard catalysts are generally mixtures of silica and alumina or natural or synthetic aluminium silicate zeolites. 

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

Crystalline Silica. Quartz sand is of course the principal raw material for the production of glass (qv). Cristobalite and 3-quartz are used in glass ceramics (qv), ie, ceramics produced by the controlled crystallization of glass. Silica is a main constituent of ceramics (qv). For example, refractory silica brick containing small amounts of A O is used as roof brick for open-hearth furnaces at temperatures >1600° C (see Refractories). Silica sand or flour (ground quartz) is the raw material for soluble silicates, such as sodium silicate, which is consistently ranked as one of the top 50 U.S. industrial chemicals (98) (see Silicon compounds, synthetic inorganic silicates). 

Food additive -microbial polysaccharides as [MICROBIALPOLYSACCITARIDES] (Vol 16) -silica as [SILICA - INTRODUCTION] (Vol21) -sodiumiodide as [SODIUMCOMPOUNDS - SODIUMHALIDES - SODIUMIODIDE] (Vol22) -sodium silicate as [SILICON COMPOUNDS - SYNTHETIC INORGANIC SILICATES] (Vol 22) -stannous chloride as [TIN COMPOUNDS] (Vol 24) -stannous chloride [TIN COMPOUNDS] (Vol 24)... 

Silica sols - [SILICONCOMPOUNDS - SYNTHETIC INORGANIC SILICATES] (Vol 22)... 

Kieselguhr is the most used support. Improvements in supports have been made synthetic silica or silicates have shown better catalyst reproducibility from batch to batch, with an increase in Ni surface area and a decrease of mean particle size. 

Traditional adsorbents such as silica [7631-86-9], Si02 activated alumina [1318-23-6]y AL O and activated carbon [7440-44-0] C, exhibit large surface areas and micropore volumes. The surface chemical properties of these adsorbents make them potentially usefiil tor separations by molecular class. However, the micropore size distribution is fairly broad for these materials (45). This characteristic makes them unsuitable tor use in separations in which steric hindrance can potentially be exploited (see Aluminum compounds, aluminum oxide (alumina Silicon compounds, synthetic inorganic silicates). 

Acid-treated clay minerals were employed as cracking catalysts in the first commercial process, the Houdry process, widely used in the early petroleum industries to produce high-octane gasoline. The Houdry process catalysts had been discussed extensively by many investigators (2) but were eventually completely replaced by synthetic silica-alumina or zeolite catalysts. Recently, the need for new catalytic materials has revived special interest in the layer lattice silicates because of their ion-exchange properties and their expandable layer structures. 

The crystal structures of synthetic silica-magnesia and Filtrol SR catalyst have not been published. However, it has been reported that silica-magnesia is converted to a crystalline nonporous magnesium silicate when heated to about 1400°F. (354). 

In this respect, the recently discovered family of materials synthetized by silicate condensation around surfactant micelles (Micelle-Templated Silica, MTS) provides unique inorganic support [11,12] due to their regular arrays of uniformly sized channels in the mesopore range of 20-100 A. This solid was recently impregnated with cesium oxides with the aim to obtain superbase catalysts [13]. Nevertheless, the leaching of the basic particles cannot be excluded. In view to avoid such possible phenomena, we have studied the covalent attachment of basic functions such as amino groups on the MTS surface... 

Fumed silica, grades, 146 In rice hulls, 145 Moisture content, 146 Natural, 146 Oil absorption, 146 Particle sizes, 146 Precipitated, 146 Specific gravity, 146 Specific surface area, 146 Synthetic, 146 Silicates, 87, 98, 123 Silicosis, 133 Mica, 133 Silylating agent, 85 Simple beam bending, 225 Single-screw compounder, 568 Sink/float procedure, 212, 216-218 Sisal fiber, 82, 86, 90, 110 Slip at the wall, 667 Slip coefficient, 211, 369-382 Slip enhancer, 381 Slip index, 376 Slip modifier, 381... 

The preparation of synthetic silica-alumina catalysts is a relatively simple one, involving the coprecipitation or cogelation of the two hydrous oxides from mixed solutions of sodium silicate and aluminum sulfate. Depending on how the solutions are mixed and on the pH and concentration of the resulting mixture, the combined hydrous oxides will be formed as a coprecipitate, which separates from a greater part of the aqueous phase, or as a true hydrogel, which embraces the entire solution volume. 

The object of this study was to apply mid-infrared spectroscopy to zeolite structural problems with the ultimate hope of using infrared, a relatively rapid and readily available analytical method, as a tool to characterize the framework structure and perhaps to detect the presence of the polyhedral building units present in zeolite frameworks. The mid-infrared region of the spectrum was used (1300 to 200 cm"1) since that region contains the fundamental vibrations of the framework (Si,Al) 04 tetrahedra and should reflect the framework structure. Infrared data in similar spectral regions have been published for many mineral zeolites (30) and a few synthetic zeolites (23, 49, 50). There is an extensive literature on infrared spectra of silica, silicates, and aluminosilicates (17). However, no systematic study of the infrared characteristics of zeolite frameworks as related to their crystal structure has appeared. 

Cleanup is performed by column chromatography. Silica/allumina or Florisil (synthetic magnesium silicate salt), deactivated or suitably activated (for instance 130 °C for 12 h ) are the most frequently used stationary phases. Their performances are checked by standard solution in order to find out the best solvent or mixture of solvents and the optimum volume to be used for selectively eluting PCBs and leaving interferents in the column. V-Hexane and dichloromethane are the most widely used solvents. Better precision on cleanup results has been observed when Florisil cartridges are used instead of silica gel ones. In some cases, in order to minimize interference from other non-PCB organic compounds, additional fractionations are performed. 

Silicates—These chemically inert synthetic amorphous silica adsorbents have an affinity for polar contaminants. The surface area, porosity, and moisture content of the silica adsorbents provide them the capability of adsorbing secondary oxidation products (aldehydes, ketones), phosphatidic compounds, sulfur compounds, trace metals, and soap. Moisture functions to hold the pores open and aid in the attraction of the polar contaminants. Most of the synthetic silicas do not have significant direct adsorption capabilities for carotenoid or chlorophyll compounds, but the removal of the other impurities enhances the efficiency of the bleaching earths (Young, 1990). 

Degussa, Technical Bulletin Pigments The Handling of Synthetic Silicas and Silicates, Pig. 28-3-2-598, 3rd Edition, May 1998. 

Silica si-li-k3 [NL, ff. L silic-, silex hard stone, flint] (ca. 1801) (silicon dioxide) n. Si02. A substance occurring widely in minerals such as quartz, sand, flint, chalcedony, opal, agate, and many more. In powdered form it is used as a filler, especially in phenolic compounds for ablative nose cones of rockets. Synthetic silicas, made from sodium silicate or by heating sihcon compounds, are useful in preventing plate-out. 

Sodium silicoaluminate n. 9Na20-67Si02-I2AI2O3. Ultrafine synthetic precipitate formed by reacting an alinninum salt with an alkali silicate. Density, 2.1 g/cm (17.5lb/gal) O.A., 125 particle size, 0.1-0.4 pm. Syn sodium aluminosihcate, synthetic silica pigment. 

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