Silica solubilization

When silica levels increase, hydroxide alkalinity measurements become increasingly important to ensure maximum silica solubilization and the reduction of risk of silica deposition. This is especially so for coil boilers because, more than any other boiler type, the use of hydroxide is critical in keeping the waterside surface of the coiled tube clean and deposit free. 

The solubility of silica in hydro-organic phases is enhanced by the rise in temperature. The rate of the silica solubilization depends on the pH and temperature of the mobile phase and also on the bonding quality of the stationary phase [40]. Silica solubility may become a serious problem when working at temperature higher than 50 C [5,22,39]. Column life is shortened. 

Organic adds which form chelates with Fe or Al apparently release silicic acid from combination with these elements in soil or conversely remove these elements from the surface of the silica, permitting it to dissolve. Uptake of silica is promoted by lowering soil pH (138). Soil can be fertilized with silica solubilized as a complex with ammonium humate, which is analogous to the catecholate complex (139)... 

The protecting groups are also used to solubilize synthetic intermediates in organic solvents, e.g. methylene chloride. Chromatography is then possible on a larger scale, since silica gel can be used as adsorbent. Six synthetic strategies have been developed (H. Kdster, 1979) ... 

Product recovery from reversed micellar solutions can often be attained by simple backextraction, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solubilization, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, e.g., to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or silica gel has also been found to cause a precipitation of the protein from the organic phase. 

He et al. (2002) used an off-line HPLC/CE method to map cancer cell extracts. Frozen ovarian cancer cells (containing 107 cells) were reconstituted in 300 pL of deionized water and placed in an ultrasonic bath to lyse the cells. Then the suspension was centrifuged and the solubilized proteins were collected for HPLC fractionation. The HPLC separation was carried out on an instrument equipped with a RP C-4 column, 250 mm x 4.6 mm, packed with 5-pm spherical silica particles. Extracted proteins were dissolved in 300 pL of DI water, and lOOpL was injected onto the column at a flow rate of 1 mL/min. Buffer A was 0.1% TEA in water and buffer B was 0.1% TFA in acetonitrile. A two-step gradient, 15-30% B in 15 min followed by 30-70% B in 105 min, was used. The column effluent was sampled every minute into a 96-well microtiter plate with the aid of an automatic fraction collector. After collection, the fractions were dried at room temperature under vacuum. The sample in each well was reconstituted before the CE analysis with 10 pL deionized water. The... 

Soil components, silica, and alumina are solubilized, in low concentration, and can react, or crystallize, to form new clays. In addition, clays from any source change over time and become simpler and simpler. Silica is more soluble than alumina and so the silica alumina ratio decreases over time. Eventually, this leads to deposits of alumina that are used as an aluminum ore for the production of aluminum metal. Although these reactions are considered to be very slow on a human timescale, they do occur. 

In the second type of chromatographic experiments chiral crown ethers of type [284] covalently attached to silica were equilibrated with solutions of racemic ammonium salts or amino-acid ester salts solubilized by addition of 18-crown-6 or alcohols in chloroform or dichloromethane (Table 66). The... 

FIGURE 12 Schematic overview of the separation principle in MEKC. Compound N is partitioned between aqueous phase represented by the EOF that moves toward the cathode in a fused silica capillary and the typical SDS micelles M. Reconstructed typical electropherogram with three peaks, t = I A neutral compound with no affinity for the micelles migrates with the velocity of the EOF. t = 2 A neutral compound with an affinity for both the micellar and the aqueous phase migrates with an intermediate velocity, t = 3 A fully solubilized neutral compound migrates with the velocity of the micelles. 

Silica is also solubilized from the igneous rocks during high-temperature reactions. This causes dissolved silica to become supersaturated, leading to the precipitation of quartz and other secondary silicates, such as albite, within the hydrothermal conduits. The formation of albite is an important reaction because it serves as a sink for Na and and a source of Ca ... 

For example, the (salen)Co(III) catalysts depicted in Figs. 11 and 12 have been isolated with concomitant purified copolymer by filtration of the polymerization solution through a short pad of silica gel (230-400 mesh) resulting in the metal catalyst being trapped on the pad and the copolymer solution eluted [33]. The (salen)Co(III) catalyst was recovered from the silica gel pad upon solubilization with a methanol solution of NaBF4. In this manner, the separated catalyst could be reused without significant loss in catalytic activity and the copolymer isolated with a metal residue of only 1-2 ppm. 

NH4HF2 is used to solubilize silica and silicates in siliceous rocks of oil wells, thus to regenerate oil flow as a neutralizer for alkalies in textile plants and commercial laundries for removing stains from fabrics for treating, polishing and rapid frosting of glass plates, window panes, picture frames, ampoules and optical lenses to produce pure salts of metal fluorides in treat-... 

Metallic beryllium is produced by reduction of beryllium halide with sodium, potassium or magnesium. Commercially, it is obtained primarily from its ore, beryl. Beryllium oxide is separated from silica and alumina in ore by melting the ore, quenching the solid solution, and solubilizing in sulfuric acid at high temperatures and pressure. Silica and alumina are removed by pH adjustment. Beryllium is converted to its hydroxide. Alternatively, beryl is roasted with complex fluoride. The products are dissolved in water and then pH is adjusted to produce beryllium hydroxide. 

Fig. 4 Schematic illustration of synthesis of multifunctional nanoparticles starting from a w/o microemulsion, b solubilization of fluorescent dye in the microemulsion core, c formation of silica nanoparticle and encapsulation of fluorescent dye, d condensation of silane ligand and chelation of Gd(lll), e post coating with silica, and f extraction of nanoparticles...

In 1968, Stober et al. (18) reported that, under basic conditions, the hydrolytic reaction of tetraethoxysilane (TEOS) in alcoholic solutions can be controlled to produce monodisperse spherical particles of amorphous silica. Details of this silicon alkoxide sol-gel process, based on homogeneous alcoholic solutions, are presented in Chapter 2.1. The first attempt to extend the alkoxide sol-gel process to microemul-sion systems was reported by Yanagi et al. in 1986 (19). Since then, additional contributions have appeared (20-53), as summarized in Table 2.2.1. In the microe-mulsion-mediated sol-gel process, the microheterogeneous nature (i.e., the polar-nonpolar character) of the microemulsion fluid phase permits the simultaneous solubilization of the relatively hydrophobic alkoxide precursor and the reactant water molecules. The alkoxide molecules encounter water molecules in the polar domains of the microemulsions, and, as illustrated schematically in Figure 2.2.1, the resulting hydrolysis and condensation reactions can lead to the formation of nanosize silica particles. 

Jain et al. (33) used the microemulsion system Triton X-100/cyclo-hexane/hexanol/water/ammonia to prepare silica nanoparticles with entrapped bioactive macromolecules fluorescein isothiocyanate-dextran (FITC-Dx) (mol. mass 19.6 kD), [125I]tyraminylinulin (mol. mass 5 kD), and horseradish peroxidase (HRP) (mol. mass 40 kD). The biomolecules were first solubilized in the microemulsion, and the alkoxide (TMOS) was then added. To ensure small particle sizes, the reaction was conducted under ice-cold temperatures (in a refrigerator for 72 h). 

Defoaming agents are in three principal categories, but sometimes are used in combination II) surfactants made soluble. (2) dispersions of hard panicles, and f3) dispersions of soft panicles. The fatty acid-fatty alcohol combination in hydrocarbon oil is an example of a solubilized surfactant defoaming formulation Paraffinic waxes and laity amides may be used in soft-particle formulations. The most common of the hard-particle formulations is silica or a mineral coated with silicone dispersed in a vehicle. A particle size as small as 0.1X2 micrometer may be optimal. 

The drawback of silica based material is the pH stability. Silica begins to dissolve at pH beyond 8, and the higher the pH the higher the solubilization. Polymeric phases with polystyrene... 

The advances in column and instrument technology have significantly enhanced HPLC performance in recent years. Results comparing the effects of various column packings on TG separation by RP-HPLC were presented by El-Hamdy and Perkins (87). Six commercially packed columns produced by different manufacturers were used PARTISIL ODS-1 and ODS-2 octadecyl-bonded silica of 10-/rm partical size, ZORBAK-ODS octadecyl-silica of 6-7-/rm diameter (250 X 4.6-mm ID), 5-/rm octyl-bonded spherical silica LC-8, 5-//m methyl-bonded spherical silica LC-1, and a 5-/rm octadecyl-bonded spherical silica LC-18 (150 X 4.6-mm ID). The mobile phase employed consisted of mixtures of methanol/acetone/isopropanol/acetonitrile ranging from l 0 3 4to 1 6 3 4. Triglycerides were solubilized in either THF or acetone at 100 mg/ml for each compound. 

Iron. Industrial hygiene chemists have analyzed iron as the o-phenanthrollne or thiocyanate complexes (6,13). In the AAS analysis at 248.3 nm with air-acetylene atomization, nickel and silica are interferences. If iron in ferro-vanadium must be analyzed, a more oxidative solution than the ntiric acid wet ashing of P CAM 173 is required. Nitric acid-hydrofluoric acid will solubilize refractories containing iron. 

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