Silicate glass: soluble species

Modern analytical instrumentation has been used in the last 23 years for determining commercially important characteristics of soluble silicates, and the nature of silicate species in silicate glasses and solutions. The classical wet methods for assay of silicate solutions are alkali titration and gravimetric determination of silica, which can also be determined, with lesser precision, by the alkali fluosilicate method. 

Silicagel. Silicagel is usually prepared from sodium silicates, which are produced as glasses with a stoichiometry of Si02/Na20 = 0.6-0.25. At the right pH they arc soluble in water and the solution contains mixtures of silicate anions monomeric, dimeric, trimeric species, etc. (Fig. 3.13). 

We believe that a similar water vapor solubility enhancement of alkali vapor transport is possible in soda-lime-silica glass systems, and work is in progress to verify this. Some of the disparities between various glass vaporization studies may well result from variations in water content and, hence, alkali activities. The common explanation for water vapor enhanced alkali vapor transport over silicates has revolved around formation of volatile NaOH (77) and KOH (53) species. However, no direct test for the presence of these species has been made, and the possibility of water vapor enhancement of atomic Na and K transport exists in these systems. 

The bifluorides syn. hydrogendifluorides, are crystalline solids containing the HF2 species. Examples include sodium bifluoride and potassium bifluoride. They are crystalline solids soluble in water or water-alcohol solutions and extremely corrosive to metals, glass, and other siliceous materials. They are used as etchants. 

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