Silicates yields

Preparation.—Several methods6 have been employed to isolate metallic lithium from its salts. The silicates yield lithium oxide, carbonate, or sulphate by ignition with the corresponding calcium or barium compound.6 The solution obtained by extraction with water is freed from heavy metals by precipitation, and the lithium and other alkali-metal salts present converted into carbonates.7 The methods employed in the separation of the mixed carbonates depend on the comparative insolubility of lithium carbonate in water, and on the... 

Cr/alumina can also be acidified by a small amount of silica applied as a surface layer [628,629]. Treating the alumina with an organic silicate, yielding 5-10 wt% Si02 after calcination, results in a substantial increase in acidity, and a corresponding improvement in activity. As little as... 

Silicon dioxide is an acidic oxide, though no acids of silicon have ever been isolated. The oxide does not react directly with water. Acidification of a water solution of a soluble silicate yields only hydrous Si02 (Mortimer 1983). 

I d ous glass and quartz are also basically similar, but tb i lwo.a sorbents h ive not been used much in adsorption chromatography. Chromato-I l aphic silicas are amorphous, porous solids which can be prepared in a wide range of surface areas and average pore diameters Variation Of solution pH during the acid gelation of sodium silicate yields silicas with... 

Herrera [6]... (following on the work of Moore and Evans [7] and Bastian [8])... concluded that colloidal silicates yield structures most like natural forms when produced from reaction-mixtures of very low concentration, when contact between precipitating agent is made slowly and when the viscosity of the reacting solution is great. 

The two most important constituents of Portland cement are alite, a form of tricalcium silicate, and belite, a form of dicalcium silicate. In their hydration both calcium silicates yield—in addition to calcium hydroxide—a nearly amorphous calcium silicate hydrate phase (C-S-H phase), and this hydration product is mainly responsible for the strength and other physico-mechanical properties of the hardened cement paste. 

The addition of a salt of a polyvalent metal to a solution of a soluble silicate results in formation of a precipitate of a metal silicate. In this precipitate, silicate ions are presumably linked together by the metal ions to form an insoluble network. On the other hand, the addition of a salt of a monovalent metal, for example, sodium chloride, to a solution of sodium silicate yields a precipitate that will redissolvc if the system is diluted with water. 

Certain anhydrous crystalline silicates yield layerlike crystalline hydrated silicas with the approximate formula (HjSiiO ),. These are cited to illustrate the complexity of such apparently simple compounds. 

The selection of SX as the purification route serves several purposes in this flow sheet. Sulfnric acid leaching of silicates yields silicic acid, Si(OH)4, in solntion which, if treated incorrectly, may form silica gel that impairs S-L separation. Leaching can be carried out so that a fairly dilute liquor is obtained, thereby minimising solnble losses of the valuable metal and avoiding silica gel formation (Matthew and... 

If these bond expansion coefficients are used, computer modelling of the structures of various end members of the high-quartz-type and keatite-type alumino-silicates yields coefficients of thermal expansion in reasonable qualitative agreement with the measured ones. 

The weathering of silicates yields soluble silicon as species such as H4Si04, and residual silicon-containing minerals (clay minerals). 

Uses Cheiating auxiliary suspending agent helps to disperse sodium silicate yielding softer goods after washing safe for use in dyebath with direct and reactive dyes, incl. metal-complex types... 

All silicon compounds on oxidation yield silica or silicates these are difficult to detect but silica (given by silicates after acid treatment) is insoluble in all acids except hydrofluoric acid. 

Mannosides are difficult to obtain since here a 2-O-acyl group blocks the -position. 2-O-Benzyl-a-mannosyl bromides give, however, high yields of pure -glycosides with a heterogeneous silver silicate catalyst preventing anomerization and SnI reaction of the bromide H. Paulsen, 1981 B, Q. 

To a mixture of ethyl 5a-cholestan-3-one 2a-xanthate (2 g, 3.95 mmol) and 100 ml methanol is added sufficient ether to completely dissolve the solids. Sodium borohydride (90 mg, 2.36 mmol) is added directly to the reaction flask and the solution is stirred at room temperature for 4 hr. (The use of an excess of sodium borohydride and an extended reaction time produces 5oc-cholestan-2a,3a-thiirane.) The reaction is diluted with 200 ml ether and washed several times with ca. 100 ml water, dried (MgS04) and the solvent is removed under vacuum. The crude sticky gum is chromatographed on a column of 85 g silicic acid. The hexane eluates contain 5a-cholest-2-ene. Ethyl 5a-cholestan-3a-ol 2a-xanthate is obtained in ca. 30% yield by subsequent elution with benzene hexane (1 7) and the desired ethyl 5a-cholestan-3 -ol 2a-xanthate is eluted with ether hexane (1 3) in ca. 30% yield. 

TS-1 (titanium silicate molecular sieve), H2O2, MeOH, reflux, 4-18 h, 60-64% yield. ... 

This reaction mixture is kept between 0°C and -i-5°C for six hours, with agitation and under an inert atmosphere, then 5 cc of a 0.2N solution of acetic acid in toluene are added. The mixture is extracted with toluene, and the extracts are washed with water and evaporated to dryness. The residue is taken up in ethyl acetate, and then the solution Is evaporated to dryness in vacuo, yielding a resin which is dissolved in methylene chloride, and the solution passed through a column of 40 g of magnesium silicate. Elution is carried out first with methylene chloride, then with methylene chloride containing 0.5% of acetone, and 0.361 g Is thus recovered of a crude product, which is dissolved in 1.5 cc of isopropyl ether then hot methanol Is added and the mixture left at 0°C for one night. 

To improve the yield of mono- and dimethylamines, a shape selective catalyst has been tried. Carhogenic sieves are microporous materials (similar to zeolites), which have catalytic as well as shape selective properties. Comhining the amorphous aluminum silicate catalyst (used for producing the amines) with carhogenic sieves gave higher yeilds of the more valuable MMA and DMA. ... 

The crude product is dissolved in benzene-hexane (1 1) and applied to a column containing 125 g. of silicic acid (Note 10). Elution with the same solvent gives traces (less than 5 mg. each) of the two fast-moving components in fractions 2 and 4 (125-ml. fractions) and chromatographically pure cholane-24-aI in fractions 5-8 (Note 11). Evaporation of the pooled fractions yields 870 mg. (84%) of the pure crystalline aldehyde, m.p. 102-104°. Recrystallization from 5 ml. of acetone raises the melting point to 103-104° (Note 12). 

This material was applied to a silicic acid-Celite column. The 10% ethyl acetate (in choloroform) eluate from this column yielded... 

Glocker and Frohnmayer determined the characteristic constant c for nine elements (Reference 2, Table 4) ranging in atomic numbers from 42 (molybdenum) to 90 (thorium). They proved that identical results could be obtained with the sample in the primary (polychromatic) or in the diffracted (monochromatic) beam. The method was applied with good results to the determination of barium in glass of antimony in a silicate of hafnium in the mineral alvite and of molybdenum, antimony, barium, and lanthanum in a solution of their salts—for example, 5.45% barium was found on 90-minute exposure by the x-ray method for a glass that yielded 5.8% on being analyzed chemically. 

The measured potential is thus a linear function of pH an extremely wide (10-14 decades) linear range is obtained, with calibration plots yielding a slope of 59 mV per pH unit. The overall mechanism of the response is complex. The selective response is attributed to the ion-exchange properties of the glass surface, and in particular the replacement of sodium ions associated with the silicate groups in the glass by protons ... 

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