Glass is a mixture of metallic silicates, usually containing an alkali metal. It has no definite crystalline structure, absorbs, refracts, or transmits light, and becomes softer as its temperature increases. The main types of glass are soda lime glass, which is cheap and used for windows and containers; potash-lime glass, which fuses at high temperatures; and potash-lead glass, which has a high refractive power and is used for lenses and prisms. Each type has different chemical properties and melting temperatures depending on its composition and intended uses.
2. What is glass?
• Mixture of number of metallic silicates, one of which is usually that of
an alkali metal
• Transparent or translucent
3. Properties
• Absorbs, refracts or transmits light
• Has no definite crystalline structure
• No sharp melting point
• Affected by alkalies
• Not affected by air or water
• Not easily attacked by chemical reagents
• Possible to weld pieces of glass by fusion
• Available in different colors
• Is transparent and translucent
• Becomes soft when heated and softer with rise in temperature
4. Types of Glass
• Soda lime or commercial glass: mixture of sodium silicate and
calcium silicate
• Available in clean and clear state
• Is cheap
• Is easily fusible at comparatively low temp
• Possible to blow or weld articles made from this glass with the help of simple
sources of heat
• Uses: used to manufacture glass tubes and other laboratory apparatus, plate
glass, window glass, etc.
5. • Potash-lime glass: also k/a Bohemian glass or hard glass; mixture of
potassium silicate and calcium silicate
• Fuses at high temperatures
• Not easily affected by water and other solvents
• Does not melt so easily
• Uses: used in manufacture of glass articles which have to withstand high
temperatures
• Potash- lead glass: also k/a flint glass; mixture of potassium silicate
and lead silicate
• Fuses very easily
• Easily attacked by aqueous solution
• Possesses bright lustre and great refractive power
• Specific gravity is about 3 to 3.30
• Turns black and opaque if it comes into contact wity reducing gases of furnace
during heating
• Uses: manufacture of artificial gems, electric bulbs, lenses, prisms, etc
6. • Common Glass: also k/a bottle glass; mixture of sodium silicate,
calcium silicate and iron silicate
• Fuses with difficulty
• Brown, green or yellow in color
• Easily attacked by acids
• Uses: manufacture of medicine bottles
• Borosilicate Glass: made mainly of 70-80% silica, 7-13% boric oxide
with smaller amounts of alkalis (sodium and potassium oxides) and
aluminium oxide.
• Low alkali content make it chemically durable and thermal shock resistance
• High softening point
• Does not break when temperature changes quickly
• Uses: for laboratory apparatus, pharmaceutical containers, glass fibres in
reinforced plastics
