Water silicates, anhydrous

Thus, in the dehydration of monomineralic rocks hydrous silicate = anhydrous silicate + H2O—the fugacity of water at a given temperature T is constant in the whole pile. The process of dehydration will go on irreversibly only in the case of a decrease in / h,o removal of water from the pile... 

Figiue 4.15 shows the basic structure of cement-based materials, exemplified by a cement-mortar lining. The binder consists of hydrated cement produced by reacting water with anhydrous cement, which contains calcimn silicates and calcium aluminates in various proportions. 

Alternatively, as described in U.S. Patent 3,341,557, 6-dehydro-17-methyltestosterone may be used as the starting material. A mixture of 0.4 g of cuprous chloride, 20 ml of 4 M methylmagnesium bromide in ether and 60 ml of redistilled tetrahydrofuran was stirred and cooled in an ice bath during the addition of a mixture of 2.0 g of 6-dehydro-l 7-methyl-testosterone, 60 ml of redistilled tetrahydrofuran and 0.2 g of cuprous chloride. The ice bath was removed and stirring was continued for four hours. Ice and water were then carefully added, the solution acidified with 3N hydrochloric acid and extracted several times with ether. The combined ether extracts were washed with a brine-sodium carbonate solution, brine and then dried over anhydrous magnesium sulfate, filtered and then poured over a 75-g column of magnesium silicate (Florisil) packed wet with hexanes (Skellysolve B). The column was eluted with 250 ml of hexanes, 0.5 liter of 2% acetone, two liters of 4% acetone and 3.5 liters of 6% acetone in hexanes. 

The combined extracts were washed with water, dried over anhydrous sodium sulfate and concentrated to approximately 35 ml. The solution was chromatographed over 130 g of Florisil anhydrous magnesium silicate. The column was developed with 260 ml portions of hexanes (Skellysolve B) containing increasing proportions of acetone. There was thus eluted 6a,9a-difluoro-11/3,17a,21 -trihydroxy-16a-methy 1-1,4-pregnadiene-3,20-dione-21 -acetate which was freed of solvent by evaporation of the eluate fractions. 

The second important source for the hydrosphere and the oceans are asteroids and comets. Estimating the amount of water which was brought to Earth from outer space is not easy. Until 20 years ago, it was believed that the only source of water for the hydrosphere was gas emission from volcanoes. The amount of water involved was, however, unknown (Rubey, 1964). First estimates of the enormous magnitude of the bombardment to which the Earth and the other planets were subjected caused researchers to look more closely at the comets and asteroids. New hypotheses on the possible sources of water in the hydrosphere now exist the astronomer A. H. Delsemme from the University of Toledo, Ohio, considers it likely that the primeval Earth was formed from material in a dust cloud containing anhydrous silicate. If this is correct, all the water in today s oceans must be of exogenic origin (Delsemme, 1992). 

The study of these systems may be divided on practical grounds into (1) investigations of the anhydrous oxides and silicates (taking in the first eight oxides in the list above) (2) investigations involving hydrous silicates, as well as combinations containing both carbon dioxide and water. 

When anhydrous cement mix is added to water, the silicates react, forming hydrates and calcium hydroxide. Hardened Portland cement contains about 70% cross-linked calcium silicate hydrate and 20% crystalline calcium hydroxide. 

Sodium silicate is stored and shipped as a liquid, but when exposed to air, it will turn into a hard, glass-like material. In reality, it is a glass in a totally anhydrous form the sodium hydroxide content is 34% by weight, and the remaining 66% is silicon dioxide. These proportions are theoretical, however, as an anhydrous sodium silicate is not really possible because it would always be absorbing water from the air. 

Calcium Silicate occurs as a white to off white, free-flowing powder that remains so after absorbing relatively large amounts of water or other liquids. It is a hydrous or anhydrous silicate with varying proportions of CaO and SiOi. It is insoluble in water, but it forms a gel with mineral acids. The pH of a 1 20 aqueous slurry is between 8.4 and 12.5. 

Sodium Metasilicate occurs as a white, free-flowing, granular material. It is a hydrous (pentahydrate) or anhydrous silicate having a 1 1 molar ratio of Si02 to Na20. At 30°, the anhydrous Sodium Metasilicate is easily soluble in water (270 g/ L) as is its pentahydrate (610 g/L). The pH values of 1% solutions of anhydrous Sodium Metasilicate and of its pentahydrate are about 12.6 and 12.4, respectively. 

A solution of maleic acid in methanol has also been used to dissolve the silicate phases (Til). This is quicker than the SAM method, but if the methanol contains water, ettringite may be formed and water-soluble phases, such as K2SO4, lost, while if it is anhydrous, gelling occurs the SAM method is thus preferable (S31). Extraction of the silicate phases by the trimethylsilylation method of Tamas et al. (T12) (Section 5.3.2) also leaves a residue containing the aluminate and ferrite phases. 

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