Comodoro 1571

The silicon is a chemical element of the family of the Cristallogène S, symbol If and of Atomic number 14.

It is the most abundant element on the Ground after the Oxygène (27,6%). There does not exist in a free state but in the form of made up: in the form of dioxide, the Silica (in the Sand, the quartz, the Cristobalite, etc…) or of Silicate S (in the Feldspar, the Kaolinite, etc).

It is used for a long time in the form of amorphous silicon oxide (silica or SiO2) like essential component of the Verre. It has new uses in electronics, for the production of materials such as silicones or to manufacture solar modules Photovoltaïque S.

The name derives from Latin flint , which means stone or Silex.

Characteristics

The crystals of silicon are gray with blacks, in form of needle or Hexaèdre S (cubic form). The amorphous phase is a dark powder chestnut.

Silicon is a Semi-conducteur of electricity, its conductivity electric is much lower than that of metals. It is quasi Insoluble in the Eau. It is attacked by the hydrofluoric Acid (HF) or a hydrofluoric acid mixture Acid nitric (HNO₃) according to the phase. The silicon present of the bluish metal reflections, but is not at all as Ductile as metals.

There exist three Isotope S natural of silicon: ²⁸Si (92,18%), ²⁹Si (4,71%) and ³⁰Si (3,12%). There exist also unstable artificial isotopes: ²⁵Si, ²⁶Si and ²⁷Si which is transmitting β {{exp|+}}, as ³¹Si with ³⁴Si which is transmitting β - .

Discovered

One of composed of silicon, the Silica (silicon dioxide), was already known in Antiquity. Silica was regarded as element by the Alchimiste S then the chemists. It is a very abundant compound in minerals.

Silicon was isolated for the first time in 1823 by Jöns Jacob Berzelius. It is only in 1854 that Henry Holy-Claire Deville obtains crystalline silicon.

Uses

Alloys Aluminum-silicon

The principal use of silicon as element is like element of Alliage with the Aluminum. The alloys Aluminum-Silicium ( ACE or series 40000 according to NF IN 1780-1 ) are used for the development of castings, in particular for the Automobile (for example alloy rims) and the Aéronautique (for example elements of embarked electrical motors). The Aluminum-Silicium alloys account for about 55% of the silicon worldwide consumption.

Synthesis of silicones

Semiconductor

The properties of Semi-conducteur of silicon allowed the creation of the second generation of Transistor S, then the integrated circuits (“chips”). It is today still one of the essential components for the electronic , in particular thanks to the current technological capacity making it possible to obtain pure silicon with more than 99,99999% (Tirage Czochralski, floating molten zone).

Magic of the lithography on silicon: the current commercial productions (2007) of integrated circuit carry out the prowess of an intricacy of engraving of 45 Nm on plates of 30 cm (12 inches, size of a disc 33 turns). What would make it possible to engrave 600 million furrows (either a disc of 20 million minutes, approximately 40 years of music, or about 20 billion songs to the numerical format Ogg Vorbis).

Photovoltaic

Mechanical components

Silicon present at the pure state of the high mechanical characteristics which make it use for the realization of small parts intended for certain micromecanisms and even for the manufacture of spiral springs intended for top-of-the-range keyless watches.

Microphone and nanostructure

Because of performance of the processes of engraving and formation of form with the silicum, the silicum is used for:

formation of nanoporeux silicum to dissociate the hydrogen of the oxygen of water molecule in the combustible batteries,
formation of nanopics on a surface of silicum by Reactive Ion engraving (LAUGHS) in order to connect chips of semiconductor.

Composed

See also: Silica, Glass, Quartz (mineral), Carbide of silicon

In addition to the properties of elementary silicon, many compounds of silicon have applications. Among most known:

the silica is in nature in compact form (rollers, slickenside quartz for example), or in the form of more or less fine Sable. It also industrially is obtained, in powder form. It has many uses:

the glass is manufactured since millenia while dissolving Sable mainly made up of SiO₂ with carbonate CaCO₃ calcium and sodium carbonate Na₂CO₃. Glass can be improved by various additives.
the sand of silica is one of the components of the Céramique S.
the quartz form of superb crystals, is used like transparent material, more resistant to heat than glass (bulb of halogenous lamps). It is also much more difficult to melt and work.
silica intervenes at the sides of carbon in the manufacture of the pneumatic energy savers.
silica very fine is used as component of additives for the Béton S high performance.

ferro-silicon, silicocalcium, are used like elements of addition in the development of the Acier or the cast iron.

the carburizes silicon has a crystalline structure similar to that of the Diamant; its hardness of it is very close. It is used like Abrasif or in form Céramique in the tools for machining.

silicate CaSiO₃ the calcium is one of the components of the Ciment S.

It should be announced, to avoid a frequent mistranslation since English, that English silicon means silicon, while silicone corresponds well to silicone. On its side, " silica" indicate silica.

In nature

Minerals

Organic molecules

Silicon is in certain organic molecules, like the Silane S - méthylsilanetriols, diméthylsilanediol -, the silatranes.

Biology of silicon

The diatoms, present in the Plankton, take part in the geochemical cycle of silicon in the seas, because they extract silica to form their external membranes.

The human organism contains between 200 Mg and 7 G of silicon, according to the sources. Silicon finds in all the glycosaminoglycanes and polyuronides: chondroïtine sulfate, dermatan-sulfate, kératan-sulfate, héparan-sulfate and heparin. The Hyaluronic acid is the macromolecule richest in silicon. Silicon is also implied in the synthesis of the Collagène (3 to 6 atoms of So per chain alpha) and of the elastin. Silicon is constituent important of the arterial wall. The Aorte is being the fabric which contains some more with the Peau and the thymus. The silicon rate in these fabrics decreases with the age in very important proportions (loss higher than 60 70%).

Silicon would potentiate the action of Zinc (Zn) and Copper (Cu) and would allow the fixing of Calcium (Ca). The drink cereals and water (of which the beer manufactured starting from water and of cereals) bring naturally the sufficient quantity (25 Mg per day) to satisfy the needs (approximately 5 mg/jour). The Afssa (French Agency of Public health of Food) did not define nutritional contributions advised for silicon because they are largely covered by the food.

By abuse, some speak about “organic silica”. It seems that this denomination is rather a commercial process in the field of the parallel medicines.

Hypothetical biochemistry containing silicon

To the limit of science and science fiction, multiple work aims at highlighting the possibility of very an other form of life, based not on carbon, but on silicon. This is based on the fact that silicon is not only tetravalent like carbon, but that it is suitable for form of the complexes penta- and hexa-coordinate charged and stable. They could have interesting catalytic properties which were explored little on the exobiologic assumptions. It should however be noted that silicon has only one low capacity to form multiple connections, since the energy of dissociation of the connections π is much weaker than that of the connections π implying carbon.

The current median position seems to be negative, silicon taking part only little in biological reactions but being used rather as support (envelopes, skeletons, gel,…).

Industrial production of silicon

Silicon does not exist naturally in a free state on the ground, but it is very abundant in the form of oxides, for example the Silice or the Silicate S. silicon is extracted from its oxide by metallurgical processes, and its level of purity depends on its final use.

Purity of silicon

One distinguishes three levels from purity of silicon, indicated according to the use:

metallurgical Silicon (purity 99%), noted Mg-silicon (in English: metallurgical rank),
Silicon of quality solar (purity 99.9999%), noted SoG-silicon (solar rank),
electronic Silicon of quality (purity 99.99999999%), noted EG-silicon (electronic rank).

Production of metallurgical silicon

To obtain free silicon (sometimes called " improperly; silicon métal" to distinguish it from the Ferrosilicon), it should be reduced; industrially, this Réduction is carried out by electrometallurgy, in a Arc furnace open whose power can go until approximately 30 M W. The total reaction of principle is a reaction of Carboréduction:

SiO₂ + C → If + CO₂

Reality is more complex, with intermediate reactions leading for example to the formation of SiC, of SiO (unstable).

In practice, silicon is introduced in the form of pieces of silica (rollers, or pieces of slickenside quartz), mixes some with Réducteur S such as wood, the Charcoal, the Houille, the Coke of oil. Taking into account the requirements for purity of the final applications, silica must be relatively pure (low content of oxide iron in particular), and the reducers carefully selected (washed coal for example).

The mixture is poured in a Creuset several meters of diameter, where plunge cylindrical electrode S in Carbone (three generally) which bring the electric output and make it possible to reach the very high temperatures which the required reactions need (around 3000°C in the area of the Electric arc, with the point of the electrodes).

Silicon obtained is collected in " poches" , with the liquid state, thanks to openings practiced in the crucible. It is then refined in these pockets, by injection of air to oxidize the Aluminum and the Calcium. Then it is separated from the " Dairy " (Oxide S produced during the various stages of the process and trained with silicon) before being solidified:

either by run in Ingot mould S or on a plane surface,
or by granulation with water (liquid silicon is then versed in water and the drops of silicon are solidified into small granules: relatively delicate operation).

The intermediate reactions leading to the reduction of silicon produce also a very fine dust of Silice Amorphe, which is pulled by hot gases (primarily air and Carbon dioxide) emitted by the furnace; in the developed countries, these gases are filtered to collect the amorphous dust of Silice, which is used as element of addition in the Béton S high performance.

According to the applications, silicon is used in the form of pieces (production of the alloys aluminum-silicon) or in the form of powder obtained by crushing (production of silicones).

Silicon for electronics is obtained starting from electrometallurgic silicon, but requires a chemical stage (purification carried out on silanes) then a whole of physical purifications, before the pulling of the monocrystals.

Preparation of silicon in its use for the electronics industry

; Preparation of So pure The operation is carried out starting from the Trichlorosilane (SiHCI₃), or of the Tétrachlorure of silicon (SiCl₄), or of the Tétraiodure of silicon (SiI₄), etc For example, by attacking silicide of Cuivre to 300°C by Hydrochloric acid it is formed trichlorosilane; this body is purified by a very thorough Distillation; it is then broken up with 950°C in the presence of Hydrogène; one obtains compact blocks of very pure silicon (process Pechiney).

; Preparation of the Monocrystal One wishes to obtain monocrystals of the type NR; however silicon obtained chemically always contains some traces of Bore and it is of type P; it is thus crystallized and one transforms it into Semi-conducteur of the type NR.

Principe:
One places in a crucible in quartz a quantity of silicon appreciably corresponding to the weight of the monocrystal to obtain; one adds the dopor donor of electrons; no impurity must disturb the Cristallisation; the operation must thus proceed in an enclosure hermetically closed, of a cleanliness " chirurgicale" , and in a neutral, or vacuum atmosphere.

Réalisation:
Around the insulating quartz enclosure the inductor of a generator high frequency is placed which makes it possible to carry the mixture If-dopeur at the temperature of fusion, that is to say 1.500°C approximately. When fusion is total, the operation of crystallization can start; for this purpose, a system precision mechanics presents the germ monocrystal in contact with the bath, then raises it vertically, very slowly, while printing a very slow rotation to him which helps with the homogenization. The germ involves the silicon which is then withdrawn from the action of induction HF; if thus cools and crystallizes according to the scheduling fixed by the germ.

The operation is very delicate; the speed of lift must be constant in order not to disturb the formation of the crystal; the temperature of the bath must be also constant, except for 0,1°C (and this towards 1.500°C). The homogenization, helped by the two movements of lifting and rotation, is paramount; indeed, as the operation progresses, the bath is likely to see its concentration in impurities increasing if those present more affinity for the liquid phase than for the solid phase.

The monocrystal obtained is appeared as an about regular cylinder, from 25 to 50 mms in diameter; one divides it at his two ends: the head, which is very pure, will be used as germ for a later operation; the bottom, which is likely not to be rather pure, is rejected.

; Preparation of the discs

Conditions with remplir:
Because of the very high price of single-crystal silicon, it is necessary to avoid the matter loss during the preparation of the discs. Those are very fragile; it is thus necessary to avoid very forced being able to deform them or break them. In addition, the surface quality of the discs must be as perfect as possible. Finally the treatment should not “pollute” the monocrystal.

Le tronçonnage:
Silicon is cut out out of discs from 0,2 to 0,3 mm thickness by means of a circular saw of high degree of accuracy. Work is carried out in water in order to avoid any heating and any pollution. Waste being important, muds are filtered and silicon powders it is recovered and used again.

Rodage of the faces:
The purpose of it is to eliminate the irregularities of surface caused by the grains from diamond dust during slicing; it is carried out with powder of Carborundum. After mechanical grinding, a chemical grinding comes to remove the last irregularities and the surface layer which can be polluted. For this purpose, one uses baths of Acide S forts (acid hydrofluoric and nitric); then the discs are rinsed carefully and dried. This chemical attack can be replaced or supplemented by an electrolytic polishing .

; Cutting of the pastilles One cuts out the discs in a very great number of pastilles, with precision, the width of the feature of cutting being as weak as possible (0,125 to 0,15 mm). The burs of cutting are then eliminated by chemical attack followed by a rinsing.

See too

silicon|silicon

References

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