Anhydrous sodium silicate glasses

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. 

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. 

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. 

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. 

Synonyms Disodium metasilicate Disodium monosilicate Silicic acid, disodium salt Sodium metasilicate anhydrous Sodium silicate Soluble glass Water glass... 

Sodium silicate solution of a Si02 Na20 ratio of ca. 3.5 is predominantly produced from soda ash and quartz sand by the fnmace process. The anhydrous sodium silicate cullets that are obtained by melting together these two basic raw materials are dissolved in water nnder hydrothermal conditions and the resnlting water glass liquor is filtered and blended to the sodium silicate solution of desired purity and composition [1,5-21,44,45,47,98,99,143]. 

H2O were prepared by either dehydrating commercial sodium silicate solutions or by autoclaving anhydrous glasses of comparable compositions. Regardless of their origin, dealkalization kinetics of these hydrosilicates favored high water content and lower alkali content. 

Decomposition by alkaline fusion Fusion with an alkali metal carbonate, usually anhydrous sodium or potassium carbonate or their mixture, decomposes glass samples very effectively. This occurs above the melting point of the carbonate(s) Na2C03, 853°C K2CO3, 903°C KNaC03, 712°C. If it is known that the glass does not contain boron, the fusion sample is fused with a mixture of sodium carbonate and borax to decrease the fusion temperature. The complex silicate network is broken down, and monosilicates are formed. 

Soda Ash. Anhydrous sodium carbonate, Na2C03. A major constituent of most glass batches. Together with sodium silicate it is used to deflocculate clay slips. 

A4.4.1 Plug a 10 mL disposable pipet with glass wool. Add the equivalent depth of 1 mL anhydrous sodium sulfate. Add the equivalent depth of about 2 mL magnesium silicate. Top off the column with the equivalent depth of 1 mL anhydrous sodium sulfate. Tap the column gently. Optionally, one may use a commercial clean-up cartridge (1000 mg packing). 

A4.5 Combined Magnesium Silicate and Silica Gel Column Clean-up—Prepare a silica gel column using a lO-mL disposable pipet plugged with glass wool. On top of the glass wool place 1 mL silica gel. Add to the column about 1 mL magnesium silicate and then 1 mL anhydrous sodium sulfate. 

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