Hydrated water soluble silicates

Hydrated water-soluble silicates are also known as hydrous polysUicates or dried silicate solutions. The most common soluble silicates are sodium silicates [19]. 

Three (3) classes of interactions can be described. First are the rapid reactions between soluble silicates and the polyvalent metal ions, producing insoluble metal silicates. Second, are reactions between the soluble silicates and the reactive components of the setting agent, producing a gel structure. Third, are hydrolysis, hydration, and neutralization reactions between the setting agent and the waste and/or water. 

Sodium Aluminosilicate occurs as a fine, white, amorphous powder, or as beads. It is a series of hydrated sodium aluminum silicates having Na20 Al203 Si02 molar ratios of approximately 1 1 13, respectively. It is insoluble in water and in alcohol and other organic solvents, but at 80° to 100°, it is partially soluble in strong acids and solutions of alkali hydroxides. 

An explanation of the anomalous stability of Iler s silica sols in terms of steric stabilization effects requires that oligomeric or polymeric silicate species are present at the silica-water interface and that steric repulsion results during overlap of such layers. This mechanism is appealing in that soluble silicates, usually sodium silicates, are universal dispersants of many electrostatic colloids. Again, well-hydrated silicas [2] and other colloids exposed to aqueous silicate [18] acquire high adsorption densities of aqueous silica. 

The liquid consists of water containing calcium chloride and an unspecified water soluble polymer. Calcium chloride acts as an accelerator in the hydration processes of the tricalcium silicate substance [78], It forms an acidic solution in water, and its reaction with calcium carbonate, which is basic, also helps to speed up the setting reaction. The overall effect of these components is that Biodentine sets in 9-12min, which is much faster than MTA materials based on unmodified calcium silicates [79], The set material has been shown to release calcium ions into aqueous solution [63,80] and this stimulates the deposition of hydroxyapatite in contact with simulated body fluid [81,82],... 

The Portland cement consists mostly of calcium silicate which contains major amounts of Ca and Si, a minor quantity of Al, and traces of Fe, Mg, SO4, Na and K it contains no detectable Zn. By contrast, the average composition of the Ca-Al-Fe silicate-sulphate-hydrate phase in the cement reaction products shows a marked increase in its SO4, Fe and Na contents, but indicates a major reduction in the Ca and Si contents. The implication is that the Fe, SO4 and Na from the decomposed jarosite diffuse into, and react with, the cement particles to form various Ca-Al-Fe silicate-sulphate-hydrate phases and/or gypsum. It has been established (3) that in the jarofix process, water-soluble Zn is stabilized in the cement reaction products. The greater the amount of... 

It is important to acquire information on the hydration processes that occur when cement is subjected to low temperatures. Even at temperatures below zero cement hydrates slowly, as water does not freeze due to the presence of soluble materials in the pores. The products that form at low temperatures are calcium aluminate hydrates at earlier periods and after several months, the products of hydration of tricalcium silicate. A weak endothermal peak at about 330°C could be due to the presence of silica gel and this is preceded by the appearance of calcium hydroxide and C-S-H gel.t l... 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

The opal is very similar to hyalite, mutter glass, a hydrate of silica. The composition is remarkable it ia a simple silicate of potaesa, which, from being imperfectly melted, remains somi-tranaparent, with pieces of quartz dispersed through the mass. It does not attract moisture, and is not attacked by boiling water. It differs from Ttjch s soluble glass, by containing ten per cent, more silica. 

The most important property of sodium and potassium silicate glasses and hydrated amorphous powders is their solubility in water. The dissolution of vitreous alkali is a two-stage process. In an ion-exchange process between the alkali-metal ions in the glass and the hydrogen ions in the aqueous phase, the aqueous phase becomes alkaline, due to the excess of hydroxyl ions produced while a protective layer of silanol groups is formed in the surface of the glass. In the second phase, a nucleophilic depolymerization similar to the base-catalyzed depolymerization of silicate micelles in water takes place. 

Regardless of the t)q)e of soluble metal silicates used, they are subject to the same molecular speciation in aqueous solution resulting in a mixture of monomeric tetrahedral ions, oligomeric linear or cyclic silicate ions, and polysilicate ions. Sodium metasilicate, an example of a soluble metal silicate, can be prepared in anhydrous form or in the presence of water of crystallization as the penta- or nona-hydrate. It is readily soluble in water [8]. 

Hydrated magnesium silicate (Talc, 3Mg0 4Si02 H20, CAS No. 14807-96-6) is a magnesium silicate commonly referred to as "soapstone". It is obtained from natural sources and may contain a small amount of aluminum silicate. It is composed of MgO (31.7%), Si02 (63.5%), and H2O (4.8%). It is a crystalline nonhygroscopic, odorless, tasteless powder which is practically insoluble in water, dilute mineral acids, dilute solutions of alkali halides, and alkaline hydroxides but is soluble in hot concentrated sulfuric acid. 

Silicic acid (orthosiJicic acid), H4Si04, cannot be made by the hydration of silica. The sodium and potassium salts of silicic acid are soluble in water, however and can be made by boiling silica with a solution of sodium hydroxide or potassium hydroxide, in which it slowly dissolves. A concentrated solution of sodium silicate, called water glass/ is available commercially and is used for fireproofing wood and cloth, as an adhesive, and for preserving eggs. This solution is not sodium oi thosilicate, Na SiO, but is a mixture of the sodium... 

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