Glass (Short
Note)
Definition
Glass is a hard material that is
usually transparent made by cooling certain molten materials in such a manner
that they do not crystallize but remain in amorphous state.
Glass is considered to be a super
cooled liquid, i.e. the solid in which the molecules are present as aggregates
as in liquid, and are not present in any definite pattern.
Preparation of Glass
The principle ingredients of all
types of glass are sand or silica (SiO2). Therefore, glass is one of the most
important artificial silicates. For example, the ordinary soft glass or Soda
Glass is a mixture of Sodium Silicate (Na2SiO3) and Calsium Silicate (CaSiO3).
Soda glass is manufactured by heating
sand (SiO2), sodium carbonate (Na2CO3) and calsium carbonate (CaCO3) in a
furnace at high temperature, i.e. 1400ºC
Types of Glass
Glass is classified in a number of
ways on the basis of its chemical composition, properties, manufacturing
process or it’s use. Some important types of glass are as follows.
1. Soft Glass or Soda Glass
Soft glass or Soda glass is an
ordinary glass which is a mixture of sodium silicate and sodium calcium
silicate. it is also known as window glass.
2. Refractory Potassium Glass
It is a mixture of potassium silicate
and calcium silicate. It has high refractive index. This glass is used for
making prism, lenses and decorative glass wear.
3. Pyrex Glass
It is boro silicated glass. The main
constituents of Pyrex Glass are boroxide (B2O3) and silica (SiO2). This glass
has no chemical durability and is soluble even in water.
4. Water Glass
Water glass is just a sodium
silicate, which is prepared by the reaction of sodium oxide (Na2O) and silica
(SiO2). This glass has no chemical durability and is soluble even in water.
5. Coloured Glass
Coloured glass is prepared by adding
certain transition metal oxides. For example copper oxide (CuO) gives light
blue coloured glass, where as cobalt oxide (CoO) gives dark blue colour,
chromium oxide (Cr2O3) gives green colour and zinc oxide (ZnO) give red
coloured glass.
6. Photochromic Glass or Photosensitive Glass
Photochromic glass produces darkness
on exposure to bright sunlight but becomes clear again in absence of light.
This glass contains silver chloride or silver bromide salts which is sensitive
to light, in presence of light, the salt is decomposed to give finely divided
black silver, in absence of sunlight, silver and chloride recombine to reform
AgCl. This glass is used in sunglasses.
7. Optical Fibres
Optical fibres are thin fibres of
silica glass of high purity. They have excellent optical transparency. This
glass is used to transmit T.V Programs, Telephone conversion, Computer output
etc. It is also used to make a design on glass. This process is called Etching
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