Glass high alkali

The ultra-high alkali oxide borate glass (composition 2 NajO BjOg) (20) does not appear to have a network system but contains discrete anions (similar to... 

Glasses with high alkali content are more susceptible to chemical... 

These high alkali pressures can be attributed to the presence of unreacted Na2C03 impurity in the original glass samples, even though care was taken to avoid this in the glass preparation. Residual carbonate impurity is a common problem with glass experimentation e.g., see Cable and Chaudhry (50). 

Figure 4. Sample No. 14122 (Roman) high alkali, coarse texture, continuous, hardness >3 Mohs, dark blue. Thefollotcing phases can be identified Egyptian Blue (white), glass (light gray), and quartz (dark gray).

C-glass, an alkali-calcium-boron-silicate-glass, with particularly high chemical resistance... 

Properties Hard, crystalline solid. D 3.98, Mohs hardness 9.0, mp 2040C, dielectric strength 480 kV/ cm, dielectric constant 9.0 (20C), coefficient of friction 0.05 micron, inert to strong acids and alkalies, excellent high-temperature stability. Can be sealed to glass. High transmission in infrared and ultraviolet. 

There are two other reasons why alkalis are important. First, in mineral processing, minerals such as chromite require fusing with an alkali to convert the element being extracted into a soluble form. Both sodium carbonate and potassium carbonate are used as fusion mixtures. Second, in the manufacture of glass, silica is fiised with either soda ash or potassium carbonate. In our view, ashes with a very high alkali content, such as those of banana wastes, can be used in place of the commercially-available alkalis. Some tests are under way to confirm this hypothesis. 

Glass is generally considered to be an inert material however, it is not chemically resistant to hydrofluoric acid and alkali. Expansive reactions between amorphous silica (glass) and alkalis (such as sodium and potassium found in high concentrations in high alkali Portland cement) could have deleterious effects if glass is used in Portland cement concrete structures [208,209]. 

A-glass (alkah) the original type, a high alkali-content material, with a chemical composition similar to that of window glass it has been largely replaced by other forms. 

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