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| Atomic Number: | 14 | Atomic Symbol: | Si | | Atomic Weight: | 28.086 | Electron Configuration: | 2-8-4 | | Shells: | 2,8,4 | Filling Orbital: | 3p2 | | Melting Point: | 1410oC | Boiling Point: | 2355oC | | Uses: | Microchips, glass, polishing etc. |
History(L. silex, silicis, flint) Davy in 1800 thought silica to be a
compound and not an element; later in 1811, Gay Lussac and Thenard probably
prepared impure amorphous silicon by heating potassium with silicon
tetrafluoride.
In 1824 Jons Berzelius of Sweden, generally credited with the discovery,
prepared amorphous silicon by the same general method and purified the product
by removing the fluosilicates by repeated washings. Deville in 1854 first
prepared crystalline silicon, the second allotropic form of the element.
SourcesSilicon is present in the sun and stars and is a principal
component of a class of meteorites known as aerolites. It is also a
component of tektites, a natural glass of uncertain origin.
Silicon makes up 25.7% of the earth's crust, by weight, and is the second
most abundant element, being exceeded only by oxygen.
Silicon is not found free in nature, but occurs chiefly as the oxide and as
silicates. Sand, quartz, rock crystal, amathyst, agate, flint, jasper, and opal
are some of the forms in which the oxide appears. Granite, hornblende, asbestos,
feldspar, clay, mica, etc. are but a few of the numerous silicate minerals.
Silicon is prepared commercially by heating silica and carbon in an electric
furnace, using carbon electrodes. Several other methods can be used for
preparing the element. Amorphous silicon can be prepared as a brown powder,
which can be easily melted or vaporized. The Czochralski process is commonly
used to produce single crystals of silicon used for solid-state or semiconductor
devices. Hyperpure silicon can be prepared by the thermal decomposition of
ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone
process.
UsesSilicon is one of man's most useful elements. In the form of sand
and clay it is used to make concrete and brick; it is a useful refractory
material for high-temperature work, and in the form of silicates it is used in
making enamels, pottery, etc. Silica, as sand, is a principal ingredient of
glass, one of the most inexpensive of materials with excellent mechanical,
optical, thermal, and electrical properties. Glass can be made in a very great
variety of shapes, and is used as containers, window glass, insulators, and
thousands of other uses. Silicon tetrachloride can be used as iridize glass.
Hyperpure silicon can be doped with boron, gallium, phosphorus, or arsenic to
produce silicon for use in transistors, solar cells, rectifiers, and other
solid-state devices which are used extensively in the electronics and space-age
industries.
Hydrogenated amorphous silicon has shown promise in producing economical
cells for converting solar energy into electricity.
Silicon is important to plant and animal life. Diatoms in both fresh and salt
water extract Silica from the water to build their cell walls. Silica is present
in the ashes of plants and in the human skeleton. Silicon is an important
ingredient in steel; silicon carbide is one of the most important abrasives and
has been used in lasers to produce coherent light of 4560 A.
Silcones are important products of silicon. They may be prepared by
hydrolyzing a silicon organic chloride, such as dimethyl silicon chloride.
Hydrolysis and condensation of various substituted chlorosilanes can be used to
produce a very great number of polymeric products, or silicones, ranging from
liquids to hard, glasslike solids with many useful properties.
PropertiesCrystalline silicon has a metallic luster and grayish color.
Silicon is a relatively inert element, but it is attacked by halogns and dilute
alkali. Most acids, except hydrofluoric, do not affect it. Elemental silicon
transmits more than 95% of all wavelengths of infrared, from 1.3 to 6.y micro-m.
CostsIn September 2008, metallurgical grade silicon cost about USD 1.45 per
pound ($3.20/kg), up from $0.77 per
pound ($1.70/kg) in 2005. HandlingMiners, stonecutters, and others engaged in work where
siliceous dust is breathed into large quantities often develop a serious lung
disease known as silicosis.
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