Symbol:Si
Boiling point:4,827'C
Electron configuration:[He]2s22p2
Atomic number:6
Atomic mass:12.01070.0008u

Silicon

Silicon constitutes about 28% of earth's crust. The mineral Quartz is the main source of silicon. It is a silicon oxide. It is used in the manufacture of glass materials. It is used in the manufacture of silicon chips, semiconductors and optical fibers. Silicon is also used in production of silica firebricks and extraction of pig iron. It is used in production of ferrosilicon. Ferrosilicon is used as deoxidizer in production of steel. It is also used as alloying element in non-ferrous alloys. The important minerals of silicon are quartz, chalcedony, agate, flint and opal. The rocks like quartzite and sand stone contain quartz. The silicate minerals found in large scale occurrence in various rocks. Silicon has electrical conductivity like that of graphite. Silicon does not react with any acid except hydrofluoric acid. It forms silicontetrafluoride after reaction with hydrofluoric acids. Silicon dissolves in hot concentrated alkaline solutions and form silicates.
Glass is the most important and widely used material after metals. Ordinary glass is a mixture of sodium and calcium silicates. It is produced by heating a mixture of sodium carbonate, calcium carbonate and silicon dioxide or quartz sand. The heating is carried out in a furnace at 1700'C. This type of glass is known as soft glass. It is easily moulded in to any shape at lower temperature. Soft glass is used for making window panes and bottles. Some special glasses are produced and used for specific purposes. These are potash glass, flint glass, Pyrex glass and crook's glass. The potash glass is hard and used for combustion tubes and chemical glass wares. The flint glass has high refractive index. It is used for making lenses. The Pyrex glass is borosilicate glass. It is used for cooking utensils and high quality glass apparatus. The crook's glass is used for special quality lenses. Coloured glasses are produced by addition of colouring agents like metal oxides.

Some are given as follows:

OreColor
Cobalt OxideBlue
Copper OxideRed
Cadmium SulphideLemon Yellow
Chromium OxideGreen
Gold ChlorideRuby Red
Manganese DioxidePurple
Iron OxideBrown
Silica has a three dimensional network structure in which each silicon is bonded to four oxygen atoms. The oxygen atoms are oriented in tetrahedral pattern around the silicon atom. Each oxygen is shared by two silicon atoms. Silicates are metal derivatives of silicic acid. Silicate structures are less close packed than other oxide structures. To get pure silica the quartz sand is heated in electric arc furnace in presence of coke. Due to heating, impurities are separated and grey crystalline silica is left behind. Pure silicon is produced by heating of silica with magnesium or aluminium. Pure silicon is used in the production of chips and semiconductors.

Silicon is a strong graphitiser. It exerts controlling effect on properties on cast iron. Silicon content in cast iron varies from 1 to 3.5%. At the time of melting of cast iron, silicon content controls the melting process. Silicon also increases the hardness, strength and toughness of cast iron. To increase the malleable character of pig iron, silicon is added up to 0.9%. Spheroidal graphite iron contains up to 2.5% silicon. Silicon is also added to stainless steel to increase hardness and strength.

Copper-Silicon alloys are known as silicon bronzes. These alloys may contain up to 4 % of silicon. Silicon increases the strength and ductility of the alloys. These alloys are used in strips, plates, wires rods, tubes, bolts, rivets, bells and propeller shafts.

Nickel-Silicon alloys are very strong, tough and hard. These are resistant to sulphuric acid, acetic acid, formic acid and phosphoric acid. These alloys are used for kettles, evaporators, reaction vessels, mixers, pipes and fittings. These alloys are also used as wires and filaments for cathode tubes and spark plugs.

Aluminium-Silicon alloys are important industrial alloys. These alloys are strong and resistant to corrosion. The properties of Aluminium-Silicon alloys depend upon the amount of silicon present. These alloys are used for production of machine parts and castings. Aluminium -Silicon -Copper alloys are also used for special applications. These alloys are used for carburetor parts and pump parts. Aluminium-Silicon -Copper-Magnesium alloys have good casting properties. These alloys are used for making of pistons of engines. Aluminium -Silicon alloys have wide use in automobile cylinder blocks. It has advantages in terms of lightness, strength and thermal conductivity. Higher thermal conductivity helps in heat transfer in the water cooling and lubricating systems. These alloys are resistant to corrosion and this property helps in increasing use of these alloys in automobile and chemical industries.