Anhydrous silica

The submitters mixed active anhydrous silica gel with water (12% v>/w) and stored it in a sealed container for at least 24 hours prior to use. A ratio of 60-80 g. of silica gel per gram of crude product was used for column chromatographic separations, and a column was chosen that would give a 10 1 height diameter ratio of adsorbent. Columns were wet-packed with distilled petroleum ether (b.p. 60-68c), and after the crude product had been applied a step-gradient was run rapidly through 2% vjv ether in petroleum ether, 5% ether, and 10% ether. The column was then eluted with 20% vjv ether in petroleum ether until the bromohydrin acetate was obtained. 

Si aluminates Ca silicates Hydrated silica Anhydrous silica... 

Arsenic trioxide reacts violently and nitrogen oxide ignites in excess fluorine. Bubbles of sulfur dioxide explode separately on contacting fluorine, while addition of the latter to sulfur dioxide causes an explosion at a certain concentration [1], Reaction of fluorine with dinitrogen tetraoxide usually causes ignition [2], Interaction with carbon monoxide may be explosive. Anhydrous silica incandesces in the gas, and interaction with liquid fluorine at — 80°C is explosive [3,4], Boron trioxide also incandesces in the gas [3],... 

Precipitated amorphous hydrated silica and fumed anhydrous silica, inorganic reinforcing agent. 

Anhydrous permanganic acid, 15 596-597 Anhydrous phosphoric acid, 18 817-818 Anhydrous rare-earth salts, 14 634 Anhydrous silica... 

In accordance with the thermodynamic consequences of the extreme activation energies associated with the formation of anhydrous silica... 

One other empirical rule. For some reason, positional isomers seem to be best resolved on anhydrous silica columns. I can t offer you a good reason why this is true. Separation of cis-/trans- and axial/equatorial isomers seems to proceed best on these normal-phase columns. 

The final loss of water yields anhydrous silica. These acids are not known as such but certain minerals may be regarded as their salts. It is probable that okenite is a disilicate, thus CaH4Si207 and also petalite, a derivative of its second anhydride, AlLi(Si2Os)2. Similarly, three molecules of orthosilicic acid, by losing two molecules of water, may unite to form trisilicic acid and it again by successive loss of one, two, and three molecules of water may yield a first, a second, and a third anhydride. The... 

Silica is used as a thickening agent in polyurethanes. The grade of silica is a fine, anhydrous silica typically sold under the name of Aerosil (Evonik. Degussa. Essen, Germany). The particle size is very fine, normally less than 40 millimicrons. The bulk density of the material is extremely low and it is very light and fluffy. Inhalation of the dust must be avoided. From the... 

Pantoprazole sodium was separately mixed in 1 1 ratios with sodium carbonate, mannitol, calcium stearate, colloidal anhydrous silica, povidone K90, crospovidone, and hydroxypropyl methylcellulose. The blends were stored at 40°C and 75% relative humidity, at 50°C and 75% relative humidity, and at 65°C for 30 days. No evidence for instability was noted, indicating that pantoprazole sodium is compatible with these common excipients. 

Silica gel (230-400 mesh) was obtained from. J. T. Baker, Inc., or E. Merck. Less silica gel (e.g., 10% wt. equiv) can be used in this step, although in this case longer reflux times are necessary to complete the decarboxylation. Note that the use of completely anhydrous silica gel (e.g., silica gel flame-dried under reduced pressure) was found to catalyze olefin isomerization in some cases and should be avoided. 

Methylindene can be fluorinated at — 78 C to afford 1,2-difluoro-2-methylindan (18, R = Me) in an isolated yield of 43% as a cis/trans mixture. The isomers are separated by chromatography on anhydrous silica gel. A similar fluorination of indene gives only the tranx-isomer of 18 (R = H). ... 

After heating, anhydrous silica contained some amount of water (0.14 mol H2O/I mol SiOa) and was composed, mainly, of large-sized particles (200-500 pm, 45.52 %). Mechanical activation in the planetary mill for 5 min leads to a dramatic increase in dispersion powders of both silica and zirconium oxide mainly contain fractions with particle size less than 10 pm. Activated mixtures 1 and 2 have approximately the same granulometric composition, no fractions with particle size in the range 50- 100 pm were observed. Mixture 3 contains fractions with fine particles which predominant in mixtures 1 and 2, as well as fractions with particle size of 50-5-100 pm and more, as in the case of mixture 4. 

BP Colloidal anhydrous silica PhEur Silica colloidalis anhydrica USPNF Colloidal silicon dioxide... 

Anhydrous silica gel Neutral Medium Extremely high Rapid General... 

Add the sintered-glass funnel to the Buchner filter system and attach the vacuum source. Fill the funnel to a depth of 2 cm using anhydrous silica. Filter the aqueous polymer solution through the silica. A blue colour will appear, indicating the Cud I) species that is formed in the presence of oxygen. The solution of polymer must be freeze-dried overnight to remove all water and leave a white solid polymer product. Yields >90% are typical. 

A sample of mixed calcium oxalate monohydrate and anhydrous silica weighed 7.020 mg. After heating to 600°C, the weight of the mixture was 6.560 mg. What was the weight of calcium oxalate in the original sample What information can be obtained by DTA that cannot be obtained by TGA Describe the components of a DTA instmment and discuss the differences between a DTA and a TGA instmment. 

The preferred solvent is water, the preferred oxide is Si02, and the preferred solute is silicic acid, a precursor to anhydrous silica. The process of such preferred embodiments comprises ... 

Culture tubes (13 by 100 mm) with Teflon-lined screw caps are filled approximately three-fourths full with G-12 mesh anhydrous silica gel (Davison Chemical Co., Baltimore, Md.), dry sterilized at 400°F for 1% hr. The tubes are then marked with the mutant numbers of the strains to be put into stock and the tubes are chilled and kept in an ice bath. About 2.5 ml of (Carnation instant) nonfat dry milk (7.5 g/100 ml dispensed 2.5 ml/tube in 13 by 100 mm test tubes and autoclaved for 10 min) is added to a 5- to 7-day-old culture (in a 13 by 100 mm test tube). The conidia are then suspended by placing the tube on a vortex mixer, and 1 ml of the resulting conidial suspension is added to the cold silica gel tube. This tube is stored at ice-water temperature until all culture tubes have been put into stock. (Silica gel heats up when the milk is added and the precooling prevents a rise in temperature which could otherwise cause inactivation of some of the conidia.) All stock tubes are then stored at room temperature for 7 days with the screw caps on loosely. After this period, the caps are tightened and the tubes are shaken to loosen and thoroughly mix the crystals. 

The in situ sol gel silica process is an alternative method of incorporating silica into rubbers. The in situ sol-gel approach, in preparing silica-reinforced rubber, is considered a novel technique. In principle, a rubber is swollen in a silica precursor, e.g. tetraethyl orthosilicate (TEOS) and the TEOS-swollen rubber is then subjected to hydrolysis and condensation reactions which could be acid- or base-catalysed. Subsequently, silica particles are generated in the rubber or rubber network. The chemical reactions involved in the formation of silica particles are shown in Scheme 7.1 where the overall reaction indicates that 1 mole of TEOS requires 2 moles of water to be converted into anhydrous silica. 

Dolino G, Vallade M (1994) Lattice dynamical behavior of anhydrous silica, SILICA, Reviews in Mineralogy, Vol. 29, Eds. PJ Heaney, CT Prewitt and G.V. Gibbs, American Mineralogist,... 

The most important incompatibility in capsules is the adsorption of active substances to excipients and vice versa. Sparingly water-soluble active substances may adsorb to non-water soluble excipients such as microcrystalline cellulose (diluent). On the other hand, the very fine glidant, colloidal anhydrous silica, can adsorb onto active substance particles. Especially for low dosed active substances, relatively large fractions may adsorb or be adsorbed. Such adsorption may delay the dissolution of the active substance, resulting in a delayed or incomplete release of the substance. This may lead to a reduced pharmaceutical availability and ultimately a lower therapeutic activity. Substances known to adsorb to microcrystalline cellulose are ethinylestradiol and dexamethasone [24]. 

Hydrochloithiazide 0.5-5 mg Acetone 2 x 3-5 mL for 15-150 mg hydrochlorthiazide 3 g diluent Mannitol with 0.5 % mA Colloidal anhydrous silica, compressed [33]... 

---