https://i2.wp.com/www.sciencebold.com/wp-content/uploads/2011/08/graph_melting-and-forming-en.jpg?fit=600%2C379 379 600 admin http://www.sciencebold.com/wp-content/uploads/2016/07/Untitled-300x114.png admin2011-08-22 02:58:002016-08-04 15:20:59Manufacture Process of Glass
Today, glass is extensively used in various purposes. The major composition of glass is silica (SiO2). Under suitable condition silicon combines with oxygen and silica is produced.
Silicon + oxygen = silica
Si + O2 = SiO2
The main source of (natural source) silica is sand. Silica melts at about 1600°C. When it is heated at high temperature it turns into glass. Such glass is used to make special kind of glassware and lab equipments. This glassware when heated to red hot and plunged into water, then also they do not break because pure silica expands due to extreme heat. The glass prepared from pure silica is very much expensive.
If sodium carbonate is mixed with silica it melts at about 800°C. Due to the reaction between silica and sodium carbonate, sodium silicate is produced.
Silica + sodium carbonate = sodium silicate + carbon dioxide
SiO2 + Na2CO3 = Na2SiO3 (water glass) + CO2
Pure sodium silicate is called water glass because it dissolves in water.
In the manufacture of ordinary glass calcium carbonate (CaCO3) is added in silica in addition to sodium carbonate. Due to chemical reaction in these compounds under suitable conditions it turns into calcium silicate which does not dissolve in water. Generally, glass is manufacture from a mixture of 50% silica, 15% sodium carbonate, 10% calcium carbonate and 25% glass pieces in a tank furnace. The glass prepared by this process is called soft glass or soda glass. From this type of glass ordinary bottle, ordinary test-tube and ordinary equipments are manufactured.
Small amount of lead monoxide (PbO) is mixed in the raw materials used to prepare soda glass to manufacture the glass for windows and doors.
In place of silica, if ordinary sand is used to manufacture glass, it will be green or brownish in color due to presence of iron oxide in sand. Ordinary glass bottles are manufactured from such glass because it is less expensive. Small quantity of metallic oxide is mixed in the composition in addition to raw materials needed, to produce colored glass. For example, cobalt oxide is used to manufacture blue colored glass, copper oxide is used to manufacture red color glass and chromium oxide for green.
A chemical boron oxide is used in place of small part of silica to manufacture such glass. Due to the sudden fluctuation in heat, these glasses are not affected. These are fine looking and attractive. Such glass is also called Pyres glass.
Lead Crystal Glass
During manufacture of such glass, in raw materials used, compounds of lead potassium are also used in small quantity. These glasses are very fine looking.
Nature of Glass
Scientists explain glass as a super cooled liquid. The molecules of glass are in a very slow motion. Therefore in old window glasses the lower portion is comparatively thicker than the top.