Silicon
Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen.
Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concrete. Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones.
Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it.
Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals. However various sea sponges as well as microorganisms like diatoms need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses.
Occurrence
Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance.[14] Silicon is usually found in the form of complex silicate minerals, and less often as silicon dioxide (silica, a major component of common sand). Pure silicon crystals are very rarely found in nature.
The silicate minerals—various minerals containing silicon, oxygen and reactive metals—account for 90% of the mass of the Earth's crust. This is due to the fact that at the high temperatures characteristic of the formation of the inner solar system, silicon and oxygen have a great affinity for each other, forming networks of silicon and oxygen in chemical compounds of very low volatility. Since oxygen and silicon were the most common non-gaseous and non-metallic elements in the debris from supernova dust which formed the protoplanetary disk in the formation and evolution of the Solar System, they formed many complex silicates which accreted into larger rocky planetesimals that formed the terrestrial planets. Here, the reduced silicate mineral matrix entrapped the metals reactive enough to be oxidized (aluminum, calcium, sodium, potassium and magnesium). After loss of volatile gases, as well as carbon and sulfur via reaction with hydrogen, this silicate mixture of elements formed most of the Earth's crust. These silicates were of relatively low density with respect to iron, nickel, and other metals non-reactive to oxygen and thus a residuum of uncombined iron and nickel sank to the planet's core, leaving a thick mantle consisting mostly of magnesium and iron silicates above.
Examples of silicate minerals in the crust include those in the pyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite and sandstone.
Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, quartz, agate amethyst, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxide, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Rather, silica is structurally a network-solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolaria and siliceous sponges.
Silicon is also a principal component of many meteorites, and is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike.
| Symbol | Si | |
| Atomic Number | 14 | |
| Atomic Weight | 28.0855 | |
| Oxidation States | +2,+4,-4 | |
| Electronegativity, Pauling | 1.9 | |
| State at RT | Solid, Metalloid | |
| Melting Point, K | 1683 | |
| Boiling Point, K | 2628 |
Interesting Facts about Silicon
- The lowest acceptable purity for electronic grade silicon is 99.9999999%. This means that for every billion atoms, only one non-silicon atom is allowed.
- Silicon is the second most abundant element in our planet’s crust. Oxygen (47.3%) and silicon (27.7%) together make up 75% of the weight of Earth’s crust. Most of the crust’s silicon exists as silicon dioxide; we are familiar with this as sand or quartz.
- Silicon is the eighth most abundant element in the Universe; it is made in stars with a mass of eight or more Earth suns. Near the end of their lives these stars enter the carbon burning phase, adding helium nuclei to carbon to produce oxygen, neon, magnesium and silicon.
- Silicon burning is the last phase of a heavy star’s life before a supernova and lasts only about one day. During this phase, helium nuclei add to silicon to make sulfur, argon, calcium, titanium, chromium, iron and nickel.
Appearance and Characteristics
Harmful effects:
Silicon is not known to be toxic, but if breathed in as a fine silica/silicate dust it may cause chronic respiratory problems. Silicates such as asbestos are carcinogenic.
Characteristics:
- Silicon is a hard, relatively inert metalloid and in crystalline form is very brittle with a marked metallic luster.
- Silicon occurs mainly in nature as the oxide and as silicates.
- The solid form of silicon does not react with oxygen, water and most acids.
- Silicon reacts with halogens or dilute alkalis.
- Silicon also has the unusual property that (like water) it expands as it freezes.
- Four other elements expand when they freeze; gallium, bismuth, antimony and germanium
Uses of Silicon
- Silicon chips are the basis of modern electronic and computing. The silicon must be ultrapure, although depending on final use it may be doped with part per million levels of arsenic, boron, gallium, germanium, or phosphorus.
- Silicon is alloyed with aluminum for use in engines as the presence of silicon improves the metal’s castability. Silicon can enhance iron’s magnetic properties; it is also an important component of steel, which it toughens.
- Silicon carbide, more commonly called carborundum, is extremely hard and is used in abrasives.
- Silica (SiO2) in sand and minerals in clay is used to make concrete and bricks. Silica, as sand, is also the main constituent of glass.
- Pure, crystalline silicon dioxide (quartz) resonates at a very precise frequency and is used in high-precision watches and clocks.
- Silicones are important silicon based polymers. Having heat-resistant, nonstick, and rubber-like properties, silicones are often used in cookware, medicine (implants), and as sealants, adhesives, lubricants, and for insulation.
How silicon is made into wafers and computer chips.
Not only about silicon: how the next generation of electronic devices may work.
