GLASS

Glass is being used as an engineering material. It is a mixture of metallic silicates, one of which is usually that of an alkali material. It is amorphous, transparent or translucent. It may also be considered as a solidified super-cooled solution of various metallic silicates having infinite viscosity. For the purpose of classification, glass may be grouped into the following three categories:

1. Soda-lime glass
2. Potash-lime glass
3. Potash-lead glass

Glass is not a single compound. It is very difficult to give any particular chemical formula for it. Numerous varieties of glass have been developed recently and it is possible to make glass lighter, safer and stronger as compared to any other building material. Glass is being used as a building material for purposes such as walls and ceilings, windows, furniture, bathroom fittings, looking glass, etc.

The chemical formulas for the three groups of glass, as classified above, are as follows:

 

      Soda-lime glass: Na₂O, CaO, 6SiO₂

      Potash-lime glass: K₂O, CaO, 6SiO₂

      Potash-lead glass: K₂O, PbO, 6SiO₂

11.1.1 Properties of glass

1. It absorbs, refracts or transmits light.
2. It can take up a high polish.
3. It has no definite crystalline structure.
4. It has no sharp melting point.
5. It is affected by alkalies.
6. It is an excellent electrical insulator.
7. It is available in beautiful colours.
8. It behaves more as a solid than most solids, in the sense that it is elastic. When the elastic limit exceeds, it fractures instead of deforming.
9. It is capable of being worked in many ways, such as blown, drawn and pressed.
10. It is difficult to cast it in large pieces.
11. It is extremely brittle.
12. It is usually unaffected by air or water.
13. Ordinary chemical reagents do not attack it.
14. It is possible to weld pieces of glass by fusion.
15. It is transparent and translucent.
16. When it is heated, it becomes softer and softer with the rise in temperature and is ultimately transformed into a mobile liquid.

11.1.2 Uses of glass as a building material

1. Glass can be used for window panels.
2. Glass blocks can be used for partitions up to 6 m for insulation.
3. Sheet glass can be used for glazing.
4. Structural glass can be used for insulation, panel walls, wall facings, enclosures, etc.
5. Potash lead glasses are used for making electric bulbs.
6. Tinted glass can be used for decorative glassworks.
7. Fibre glass reinforced plastics can be used to construct furniture, lampshades and bathroom fittings.