Silicon - Applications of the Ubiquitous Element
In Many Periods, the Uses of Silicon Compounds Have Defined the Age
Nov 8, 2008
The buildings of the towns and cities and the window glass in the houses were all made from silicon compounds. Whether as granite or sandstone, and in the forms of sand, cement and mortar, silicates have been the basis of the construction industry for as long as it has existed. The information age of the 21st century depends almost entirely on the silicon chip.
Glass is a Silicon Compound
Glass is a silicate made by melting sand, which is mainly silicon dioxide, with smaller amounts of oxides of metals such as sodium, calcium, lead or zinc. When this is allowed to cool, it slowly hardens to a solid without crystallizing.
Quartz - a Pure Form of Silicon Dioxide
Metal ores are always mixed with significant quantities of quartz, the melting point of which is very high. This causes problems during the extraction of the metal. When heated in a furnace, quartz does not melt and would quickly block the furnace. To prevent this, the ore is mixed with limestone, which reacts with the quartz to form calcium silicate, a compound with a low melting point, known simply as slag. This former unsightly waste product of the steel industry is generally disposed of by using it as a bedding material in the building of roads.
When subjected to an electric current, the particles in a quartz crystal vibrate at a fixed frequency. This permits their use to measure time very accurately in quartz clocks and watches.
Pure Silicon
The pure element, silicon, can be obtained from quartz by heating it to 2000oC with coke in an electric furnace. About 4 million tonnes of the element are produced each year. Much of this is used to make ferrosilicon steels, for which a more purified silicon is needed than that present in the ores from which ordinary steel is made. The properties of aluminium are also enhanced by the addition of 99% pure silicon.
Silicones
Silicones constitute a large group of liquid compounds in which alternate silicon and oxygen atoms are linked together to form long chains and rings. The silicon atoms are also joined to small groups of carbon and hydrogen atoms, which branch off from the main chain. These compounds remain liquid even at high temperatures, and are excellent lubricants. Cross-linking of the chains leads to the formation of rubbers of the kind used, for example, to make the boots worn by the astronauts who visited the moon.
The employment of silicones in cosmetic and reconstructive surgery is well known. They are also highly water-repellent and resistant to chemical attack, and are widely used as waterproofing for brickwork and fabrics such as tent material, as well as bathroom and window sealants.
The Silicon Chip
The semi-conductor properties of silicon have led to the information technology revolution that is set to dominate human society in the 21st century. Extremely pure silicon is required to manufacture microchips, though this needs to be ‘doped’ with other elements such as arsenic or gallium to the extent of one part per million, to facilitate its use in transistors.
When Neil Armstrong and Buzz Aldrin landed on the moon, in 1969, something approaching 90% of all the silicon chips in the world were used to get them there. Now, they are present in everything from computers to cars to cameras, and from washing machines to mobile phones. Much telephone communication is now reliant upon optical fibres made from that other silicon compound, glass.
Further Reading: Silicon, the Element That is Everywhere
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