Sodium silicate glass, hydratable

Durable Glass by Reconstitution of Hydratable Sodium Silicate Glasses... 

T. Uchino, T. Sakka, K. Hotta and M. Iwasaki, Attenuated Total Reflectance Fourier-Transform Infrared Spectra of a Hydrated Sodium Silicate Glass, J. Am. Ceram. Soc. 72 (11), 2173-2175, (1989). 

Soluble sodium silicate glass sobd and Uquid (anhydrous). Excludes quantities consumed in the manufacture of meta-, ortho-, and sesquisiUcates. Includes quantities consumed in the manufacture of glass powder, hydrated glasses, and precipitated products. Shipment figures include unspecified amounts shipped to other plants for the manufacture of meta-, ortho-, or sesquisiUcates. 

Anhydrous sodium silicate glasses which are composed of between 12 and 21 wt. % Na20 are difficult to form into useful, dur-ableglass objects because of their rapid phase separation or crystallization. However, they hydrate easily in an autoclave to contain up to 40 weight percent water. These sodixam hydrosilicates are thermoplastic in behavior, but more Importantly the molecular water provides a means for dealkalizing the silicate structure. 

Sample Preparation. Two methods were used to produce sodium silicate glass samples for this study. The primary method used conventional glass melting techniques to produce compositions ranging from 12 to 21 wt. % Na20. Batch ingredients, African sand, sodiiam carbonate, and sodium nitrate, were melted at 1600 C for six hours in platinum crucibles, poured into patties and fine ground into 1 1/2" diameter discs with thickness of one to four millimeters. These anhydrous discs were fully hydrated in a one cubic foot autoclave under saturated steam conditions and stored in controlled relative hiimidity desiccators at room temperature. 

Hydrosilicate Compositions Hydration/Pehydration. For the purpose of demonstrating the feasibility of the reconstitution process the work reported here used only cut discs or plates of sodium silicate glass. In this way the dimensions of the sample could be easily controlled and dealkalization data was more meaningful. In those cases where thermally molded items, such as lens shapes, were processed the results were identical. 

Table I shows several sodium silicate glass discs (2mm x 38mm dia.) that were hydrated at 140 C in 100% relative humidity in an autoclave. The water contents range from about 21% to 41% for glass containing 12.4% and 21.4% NaaO, respectively. Hydration was directly proportional to alkali content and exposure time at 140 C. It is also directly proportional to autoclave temperature.

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. 

One thousand grams of hydrated sodium tungstate is dissolved in 2000 ml. of water. To this solution is added 75 g. of a solution of water glass (density 1.375). The mixture is stirred briskly with a motor stirrer and heated to boiling while 600 ml. of hydrochloric acid (density 1.18) is added a drop at a time from a separatory funnel. This operation takes about 90 minutes. The slight precipitate of silicic acid is filtered off, and the mixture cooled. Four hundred ml. more of the concentrated hydrochloric acid is added, and the solution cooled again. This solution... 

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... 

Silica Mortars Silica mortar is a strictly acid and heat resistant material, handling all acids except HF and acidic fluorides at pH 0-7 and thermally stable up to 2000°F. A relatively recent self-curing silica mortar contains only borosili-cate glass powder, silica sol and crushed silica with no metallic constituents. This avoids both the sulfation-hydration reaction of the sodium silicates and the alum formation problems of the potassium silicates. Like the silicate mortars, silica mortars also resist organic chemicals. 

Potassium chloride is reacted with carbon dioxide in precarbonated isopropylamine solution under pressure in an autoclave. Potassium hydrogencarbonate precipitates and the amine is converted into isopropylamine chlorohydrate. The potassium salt is isolated by filtration, washed free of amine and heated to convert it to the carbonate. Unreacted amine present in the filtrate is recovered by distillation. Hydrated lime is then added to convert the isopropylamine chlorohydrate back to the amine, which is also recovered by distillation. The main uses of potassium carbonate are the production of glass and sodium silicate. 

Sodium silicates are produced as glasses having SiOjtNajO molar ratios of 1.6-3.9. These are sold as lump or pulverized form, partly hydrated powders, and concentrated solutions. Potassium silicate glasses have SiOjrKjO molar ratios of 2.83-3.92 and are sold in pulverized, flake or solution form. 

Class F fly ash The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 20% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime or hydrated lime, with the presence of water in order to react and produce cementitious compounds. Alternatively, the addition of a chemical activator such as sodium silicate (water glass) to a Class F ash leads to the formation of a geopolymer. 

The silicate garden in which metallic salts grow colored trees when crystals are dropped into water glass (aqueous sodium silicate) is analogous to the fibrillars developed during the hydration process in cement. Explain. 

A fortiori, in hydrated glasses, all the water is intimately linked to the silicic polyanions. These results make it easier to raderstand the impact of water quantity on the properties of sodium silicates in aqueous solution or in the washing medium. 

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