Melting point si. Some physical and chemical properties of silicon and its compounds

Carbon is capable of forming several allotropic modifications. These are diamond (the most inert allotropic modification), graphite, fullerene and carbine.

Charcoal and soot are amorphous carbon. Carbon in this state does not have an ordered structure and actually consists of the smallest fragments of graphite layers. Amorphous carbon treated with hot water vapor is called activated carbon. 1 gram of activated carbon, due to the presence of many pores in it, has a total surface of more than three hundred square meters! Due to its ability to absorb various substances, activated carbon is widely used as a filter filler, as well as an enterosorbent for various types of poisoning.

From a chemical point of view, amorphous carbon is its most active form, graphite exhibits medium activity, and diamond is an extremely inert substance. For this reason, the chemical properties of carbon considered below should primarily be attributed to amorphous carbon.

Reducing properties of carbon

As a reducing agent, carbon reacts with non-metals such as oxygen, halogens, and sulfur.

Depending on the excess or lack of oxygen during the combustion of coal, the formation of carbon monoxide CO or carbon dioxide CO 2 is possible:

When carbon reacts with fluorine, carbon tetrafluoride is formed:

When carbon is heated with sulfur, carbon disulfide CS 2 is formed:

Carbon is capable of reducing metals after aluminum in the activity series from their oxides. For example:

Carbon also reacts with oxides of active metals, however, in this case, as a rule, not the reduction of the metal is observed, but the formation of its carbide:

Interaction of carbon with non-metal oxides

Carbon enters into a co-proportionation reaction with carbon dioxide CO2:

One of the most important processes from an industrial point of view is the so-called steam reforming of coal. The process is carried out by passing water vapor through hot coal. In this case, the following reaction takes place:

At high temperatures, carbon is able to reduce even such an inert compound as silicon dioxide. In this case, depending on the conditions, the formation of silicon or silicon carbide is possible ( carborundum):

Also, carbon as a reducing agent reacts with oxidizing acids, in particular, concentrated sulfuric and nitric acids:

Oxidizing properties of carbon

The chemical element carbon does not have a high electronegativity, therefore, formed by it simple substances rarely show oxidizing properties in relation to other non-metals.

An example of such reactions is the interaction of amorphous carbon with hydrogen when heated in the presence of a catalyst:

as well as with silicon at a temperature of 1200-1300 about C:

Carbon exhibits oxidizing properties in relation to metals. Carbon is able to react with active metals and some metals of intermediate activity. Reactions proceed when heated:

Chemical properties of silicon

Silicon can exist, as well as carbon in the crystalline and amorphous state, and, just as in the case of carbon, amorphous silicon is significantly more chemically active than crystalline silicon.

Sometimes amorphous and crystalline silicon is called its allotropic modifications, which, strictly speaking, is not entirely true. Amorphous silicon is essentially a conglomerate of the smallest particles of crystalline silicon randomly arranged relative to each other.

Interaction of silicon with simple substances

nonmetals

Under normal conditions, silicon, due to its inertness, reacts only with fluorine:

Silicon reacts with chlorine, bromine and iodine only when heated. It is characteristic that, depending on the activity of the halogen, a correspondingly different temperature is required:

So with chlorine, the reaction proceeds at 340-420 o C:

With bromine - 620-700 o C:

With iodine - 750-810 o C:

The reaction of silicon with oxygen proceeds, however, it requires very strong heating (1200-1300 ° C) due to the fact that a strong oxide film makes interaction difficult:

At a temperature of 1200-1500 ° C, silicon slowly interacts with carbon in the form of graphite to form carborundum SiC - a substance with an atomic crystal lattice similar to diamond and almost not inferior to it in strength:

Silicon does not react with hydrogen.

metals

Due to its low electronegativity, silicon can exhibit oxidizing properties only with respect to metals. Of the metals, silicon reacts with active (alkaline and alkaline earth), as well as many metals of medium activity. As a result of this interaction, silicides are formed:

Interaction of silicon with complex substances

Silicon does not react with water even when boiling, however, amorphous silicon interacts with superheated water vapor at a temperature of about 400-500 ° C. In this case, hydrogen and silicon dioxide are formed:

Of all acids, silicon (in its amorphous state) reacts only with concentrated hydrofluoric acid:

Silicon dissolves in concentrated alkali solutions. The reaction is accompanied by the evolution of hydrogen.

SILICON (Latin Silicium), Si, a chemical element of the IV group of the short form (the 14th group of the long form) periodic system; atomic number 14, atomic mass 28.0855. Natural silicon consists of three stable isotopes: 28 Si (92.2297%), 29 Si (4.6832%), 30 Si (3.0872%). Radioisotopes with mass numbers 22-42 are artificially obtained.

History reference. Silicon compounds, widespread on earth, have been used by man since the Stone Age; for example, from ancient times to the Iron Age, flint was used to make stone tools. The processing of silicon compounds - the manufacture of glass - began in the 4th millennium BC in ancient Egypt. Elemental silicon was obtained in 1824-25 by J. Berzelius during the reduction of fluoride SiF 4 with metallic potassium. The name "silicon" was given to the new element (from the Latin silex - flint; the Russian name "silicon", introduced in 1834 by G. I. Hess, also comes from the word "flint").

Distribution in nature. In terms of prevalence in the earth's crust, silicon is the second chemical element (after oxygen): the silicon content in the lithosphere is 29.5% by weight. It does not occur in the free state in nature. The most important minerals containing silicon are aluminosilicates and natural silicates (natural amphiboles, feldspars, micas, etc.), as well as silica minerals (quartz and other polymorphic modifications of silicon dioxide).

Properties. The configuration of the outer electron shell of the silicon atom is 3s 2 3р 2 . In compounds, it exhibits an oxidation state of +4, rarely +1, +2, +3, -4; electronegativity according to Pauling 1.90, ionization potentials Si 0 → Si + → Si 2+ → Si 3+ → Si 4+, respectively, are 8.15, 16.34, 33.46 and 45.13 eV; atomic radius 110 pm, Si 4+ ion radius 40 pm (coordination number 4), 54 pm (coordination number 6).

Silicon is a dark gray hard brittle crystalline substance with a metallic sheen. The crystal lattice is cubic face-centered; t pl 1414 ° С, t kip 2900 ° С, density 2330 kg / m 3 (at 25 ° С). Heat capacity 20.1 J/(mol∙K), thermal conductivity 95.5 W/(m∙K), dielectric constant 12; Mohs hardness 7. Under normal conditions, silicon is a brittle material; noticeable plastic deformation is observed at temperatures above 800 °C. Silicon is transparent to infrared radiation with a wavelength greater than 1 micron (refractive index 3.45 at a wavelength of 2-10 microns). Diamagnetic (magnetic susceptibility - 3.9∙10 -6). Silicon is a semiconductor, the band gap is 1.21 eV (0 K); electrical resistivity 2.3 10 3 Ohm ∙ m (at 25 ° C), electron mobility 0.135-0.145, holes - 0.048-0.050 m 2 / (V s). The electrical properties of silicon are highly dependent on the presence of impurities. To obtain silicon single crystals with p-type conductivity, dopants B, Al, Ga, In (acceptor impurities) are used, with n-type conductivity - P, As, Sb, Bi (donor impurities).

Silicon in air is covered with an oxide film, therefore, when low temperatures chemically inert; when heated above 400 ° C, it interacts with oxygen (oxide SiO and dioxide SiO 2 are formed), halogens (silicon halides), nitrogen (silicon nitride Si 3 N 4), carbon (silicon carbide SiC), etc. Silicon compounds with hydrogen - silanes are obtained indirectly. Silicon interacts with metals to form silicides.

Finely dispersed silicon is a reducing agent: when heated, it interacts with water vapor to release hydrogen, reduces metal oxides to free metals. Non-oxidizing acids passivate silicon due to the formation of an acid-insoluble oxide film on its surface. Silicon dissolves in a mixture of concentrated HNO 3 with HF, and fluorosilicic acid is formed: 3Si + 4HNO 3 + 18HF \u003d 3H 2 + 4NO + 8H 2 O. Silicon (especially finely dispersed) interacts with alkalis with hydrogen evolution, for example: Si + 2NaOH + H 2 O \u003d Na 2 SiO 3 + 2H 2. Silicon forms various organosilicon compounds.

biological role. Silicon belongs to microelements. The daily human need for silicon is 20-50 mg (an element is necessary for the proper growth of bones and connective tissues). Silicon enters the human body with food, as well as with inhaled air in the form of dusty SiO 2 . With prolonged inhalation of dust containing free SiO 2, silicosis occurs.

Receipt. Silicon of technical purity (95-98%) is obtained by reduction of SiO 2 with carbon or metals. High-purity polycrystalline silicon is obtained by reduction of SiCl 4 or SiHCl 3 with hydrogen at a temperature of 1000-1100 ° C, thermal decomposition of Sil 4 or SiH 4 ; single-crystal silicon of high purity - by zone melting or by the Czochralski method. The volume of world production of silicon is about 1600 thousand tons / year (2003).

Application. Silicon is the main material of microelectronics and semiconductor devices; used in the manufacture of glasses that are transparent to infrared radiation. Silicon is a component of alloys of iron and non-ferrous metals (in low concentrations, silicon increases the corrosion resistance and mechanical strength of alloys, improves their casting properties; in high concentrations, it can cause brittleness); iron, copper and aluminum silicon-containing alloys are of the greatest importance. Silicon is used as a starting material for the production of organosilicon compounds and silicides.

Lit .: Baransky P. I., Klochkov V. P., Potykevich I. V. Semiconductor electronics. Properties of materials: Handbook. K., 1975; Drozdov A. A., Zlomanov V. P., Mazo G. N., Spiridonov F. M. Inorganic chemistry. M., 2004. T. 2; Shriver D., Atkins P. Inorganic Chemistry. M., 2004. T. 1-2; Silicon and its alloys. Yekaterinburg, 2005.

Ministry of Education and Science of Russia

federal state budgetary educational institution higher professional education

"MATI - Russian State Technical University named after K.E. Tsiolkovsky" (MATI)

Department of "Aircraft Testing"

abstract

On the course "Chemistry"

Theme: "Silicon"

Student: Akbaev Dauyt Rinatovich

Group: 2ILA-1DS-298

Lecturer: Evdokimov Sergey Vasilievich

Moscow 2014

Silicon in living organisms

History of discovery and use

Distribution in nature

The structure of the atom and the basic chemical and physical properties

Receipt

Application

Connections

Application

1. Silicon in living organisms

Silicon (lat. Silicium), Si, a chemical element of group IV of the periodic system of Mendeleev; atomic number 14, atomic mass 28.086. In nature, the element is represented by three stable isotopes: 28 Si (92.27%), 29 Si (4.68%) and 30 Si (3.05%)

Silicon in the body is found in the form of various compounds, which are mainly involved in the formation of solid skeletal parts and tissues. Especially a lot of silicon can accumulate some sea ​​plants(for example, diatoms) and animals (for example, silicon-horned sponges, radiolarians), which, when dying, form thick deposits of silicon dioxide on the ocean floor.

In cold seas and lakes, biogenic silts enriched with silicon predominate, in tropical seas - calcareous silts with a low content of silicon. Among terrestrial plants, cereals, sedges, palms, and horsetails accumulate a lot of silicon. In vertebrates, the content of silicon dioxide in ash substances is 0.1-0.5%. AT largest quantities silicon is found in dense connective tissue, kidneys, pancreas. The daily human diet contains up to 1 g of silicon.

With a high content of silicon dioxide dust in the air, it enters the lungs of a person and causes a disease - silicosis (from Latin silex - flint), a human disease caused by prolonged inhalation of dust containing free silicon dioxide, refers to occupational diseases. It occurs in workers in the mining, porcelain-faience, metallurgical, machine-building industries. Silicosis is the most unfavorable disease from the group of pneumoconiosis; more often than with other diseases, the addition of a tuberculous process (the so-called silicotuberculosis) and other complications are noted.

2. History of discovery and use

History reference. Silicon compounds, widely distributed on earth, have been known to man since the Stone Age. The use of stone tools for labor and hunting continued for several millennia. The use of silicon compounds associated with their processing - the manufacture of glass - began around 3000 BC. e. (in ancient Egypt). The earliest known silicon compound is SiO2. 2(silica). In the 18th century silica was considered a simple body and referred to as "earths" (which is reflected in its name). The complexity of the composition of silica was established by I.Ya. Berzelius.

Silicon in the free state was first obtained in 1811 by the French scientist J. Gay-Lussac and O. Tenard.

In 1825, the Swedish mineralogist and chemist Jens Jakob Berzelius obtained amorphous silicon. Brown powder of amorphous silicon was obtained by reduction of gaseous silicon tetrafluoride with potassium metal:

4 + 4K = Si + 4KF

Later, a crystalline form of silicon was obtained. By recrystallization of silicon from molten metals, gray, hard, but brittle crystals with a metallic sheen were obtained. The Russian names for the silicon element were introduced by G.I. Hess in 1834.

. Distribution in nature

Silicon, after oxygen, is the most common element (27.6%) on earth. This is an element that is included in most minerals and rocks that make up the hard shell of the earth's crust. In the earth's crust, silicon plays the same primary role as carbon in the animal and plant kingdoms. For the geochemistry of oxygen, its exceptionally strong bond with oxygen is important. The most widely used silicon compounds are silicon oxide SiO 2and derivatives of silicic acids, called silicates. Silicon(IV) oxide occurs as the mineral quartz (silica, flint). In nature, whole mountains are composed of this compound. There are very large, weighing up to 40 tons, quartz crystals. Ordinary sand consists of fine quartz contaminated with various impurities. The annual world consumption of sand reaches 300 million tons.

Of the silicates, aluminosilicates (kaolin Al 2O 3*2SiO 2*2H 2O, asbestos CaO*3MgO*4SiO 2, orthoclase K 2O*Al 2O 3*6SiO 2and etc.). If the composition of the mineral, in addition to oxides of silicon and aluminum, includes oxides of sodium, potassium or calcium, then the mineral is called feldspar (white mica, etc.). Feldspars account for about half of the silicates known in nature. Rocks granite and gneiss include quartz, mica, feldspar.

Silicon is included in the composition of the plant and animal world in small quantities. It contains the stems of some types of vegetables and cereals. This explains the increased strength of the stems of these plants. The shells of ciliates, the bodies of sponges, eggs and feathers of birds, animal hair, hair, and the vitreous body of the eye also contain silicon.

Analysis of samples of lunar soil delivered by ships showed the presence of silicon oxide in an amount of more than 40 percent. In the composition of stone meteorites, the silicon content reaches 20 percent.

. The structure of the atom and the basic chemical and physical properties

Silicon forms dark gray crystals with a metallic sheen, having a cubic face-centered diamond-type lattice with a period a = 5.431 Å, density 2.33 g/cm ³ . With very high pressures a new (apparently hexagonal) modification with a density of 2.55 g/cm was obtained ³ . K. melts at 1417°C, boils at 2600°C. Specific heat capacity (at 20-100°С) 800 j/(kg × K), or 0.191 cal/(g × hail); thermal conductivity even for the purest samples is not constant and is in the range (25 ° C) 84-126 W / (m × K), or 0.20-0.30 cal / (cm × sec × hail). Temperature coefficient linear expansion 2.33 ×10-6 K-1; below 120K becomes negative. Silicon is transparent to long-wave infrared rays; refractive index (for l=6 μm) 3.42; dielectric constant 11.7. Silicon is diamagnetic, atomic magnetic susceptibility - 0.13×10 -6. Silicon hardness Mohs 7.0, Brinell 2.4 H/m ² (240 kgf/mm ² ), modulus of elasticity 109 Gn/m ² (10890 kgf/mm ² ), compressibility factor 0.325 ×10 -6cm ² /kg. Silicon is a brittle material; noticeable plastic deformation begins at temperatures above 800°C.

Silicon is a semiconductor that is in increasing use. The electrical properties of K. depend very strongly on impurities. The intrinsic volume resistivity of silicon at room temperature is assumed to be 2.3 ×10 3ohm × m (2.3 ×10 5 ohm × cm).

Semiconductor silicon with p-type conductivity (additives B, Al, In or Ga) and n-type (additives P, Bi, As or Sb) has a much lower resistance. The band gap according to electrical measurements is 1.21 eV at 0 K and decreases to 1.119 eV at 300 K.

In accordance with the position of silicon in the periodic system of Mendeleev, 14 electrons of the silicon atom are distributed over three shells: in the first (from the nucleus) 2 electrons, in the second 8, in the third (valence) 4; electron shell configuration 1s2 2s2 2p6 3s2 3p2 . Sequential ionization potentials (eV): 8.149; 16.34; 33.46 and 45.13. Atomic radius 1.33 Å, covalent radius 1.17Å, ionic radii Si 4+0.39Å, Si4- 1.98Å.

In silicon compounds (similar to carbon) 4-valentene. However, unlike carbon, silicon, along with a coordination number of 4, exhibits a coordination number of 6, which is explained by the large volume of its atom (an example of such compounds are silicon fluorides containing the group 2-).

The chemical bonding of the silicon atom with other atoms is usually carried out through hybrid sp3 orbitals, but it is also possible to involve two of its five (vacant) 3d orbitals, especially when silicon is six-coordinated. Having a low electronegativity value of 1.8 (against 2.5 for carbon; 3.0 for nitrogen, etc.), silicon in compounds with non-metals is electropositive, and these compounds are polar in nature. The high bonding energy with oxygen Si-O, equal to 464 kJ/mol (111 kcal/mol), determines the stability of its oxygen compounds (SiO2 and silicates). The Si-Si bond energy is low, 176 kJ/mol (42 kcal/mol); unlike carbon, the formation of long chains and a double bond between Si atoms is not characteristic of carbon. Due to the formation of a protective oxide film, silicon is stable in air even at elevated temperatures. In oxygen, it oxidizes starting from 400 ° C, forming silicon dioxide SiO 2. Also known is the monoxide SiO, which is stable at high temperatures in the form of a gas; as a result of rapid cooling, a solid product can be obtained, which easily decomposes into a thin mixture of Si and SiO 2. Silicon is resistant to acids and dissolves only in a mixture of nitric and hydrofluoric acids; easily dissolves in hot alkali solutions with evolution of hydrogen. Silicon reacts with fluorine at room temperature, with other halogens - when heated to form compounds of the general formula SiX 4(see Silicon halides). Hydrogen does not directly react with silicon, and silanes (silanes) are obtained by decomposition of silicides. Silicon hydrogens are known from SiH 4to Si 8H 18(similar in composition to saturated hydrocarbons). Silicon forms 2 groups of oxygen-containing silanes - siloxanes and siloxenes. Silicon reacts with nitrogen at temperatures above 1000°C. Si nitride is of great practical importance. 3N 4, which does not oxidize in air even at 1200 ° C, is resistant to acids (except nitric acid) and alkalis, as well as to molten metals and slags, which makes it a valuable material for the chemical industry, for the production of refractories, etc. High hardness, and Also, silicon compounds with carbon (silicon carbide SiC) and boron (SiB 3, SiB 6, SiB 12). When heated, silicon reacts (in the presence of metal catalysts, such as copper) with organochlorine compounds (for example, with CH 3Cl) to form organohalosilanes [for example, Si(CH 3)3CI], serving for the synthesis of numerous organosilicon compounds.

5. Receipt

The simplest and most convenient laboratory method for obtaining silicon is the reduction of silicon oxide SiO 2at high temperatures with reducing metals. Due to the stability of silicon oxide, active reducing agents such as magnesium and aluminum are used for reduction:

SiO 2+ 4Al = 3Si + 2Al2 O 3

Upon reduction with metallic aluminum, crystalline silicon is obtained. A method for the reduction of metals from their oxides with metallic aluminum was discovered by the Russian physicochemist N.N. Beketov in 1865. During the reduction of silicon oxide with aluminum, the released heat is not enough to melt the reaction products - silicon and aluminum oxide, which melts at 205°C. To lower the melting point of the reaction products, sulfur and excess aluminum are added to the reaction mixture. The reaction produces low-melting aluminum sulfide:

2Al + 3S = Al2 S 3

Drops of molten silicon fall to the bottom of the crucible.

Silicon of technical purity (95-98%) is obtained in an electric arc by the reduction of silica SiO 2between graphite electrodes.

2+2C=Si+2CO

In connection with the development of semiconductor technology, methods have been developed for obtaining pure and extra pure silicon. This requires a preliminary synthesis of the purest initial silicon compounds, from which silicon is extracted by reduction or thermal decomposition.

Pure semiconductor silicon is obtained in two forms: polycrystalline (by reduction of SiCl 4or SiHCl 3zinc or hydrogen, thermal decomposition of SiCl 4and SiH 4) and single-crystal (crucible-free zone melting and "pulling" a single crystal from molten silicon - the Czochralski method).

Silicon tetrachloride is obtained by chlorination of technical silicon. The oldest method for the decomposition of silicon tetrachloride is the method of the outstanding Russian chemist Academician N.N. Beketova. This method can be represented by the equation:

4+Zn=Si+2ZnCl 2.

Here, vapors of silicon tetrachloride, boiling at 57.6°C, interact with zinc vapors.

At present, silicon tetrachloride is reduced with hydrogen. The reaction proceeds according to the equation:

SiCl 4+2H 2=Si+4HCl.

Silicon is obtained in powder form. The iodide method for obtaining silicon is also used, similar to the previously described iodide method for obtaining pure titanium.

To obtain pure silicon, it is purified from impurities by zone melting in the same way as pure titanium is obtained.

For a number of semiconductor devices, semiconductor materials obtained in the form of single crystals are preferred, since uncontrolled changes in electrical properties take place in a polycrystalline material.

When single crystals are rotated, the Czochralski method is used, which consists in the following: a rod is lowered into the molten material, at the end of which there is a crystal of this material; it serves as the germ of the future single crystal. The rod is pulled out of the melt at a low speed up to 1-2 mm/min. As a result, a single crystal of the desired size is gradually grown. Plates used in semiconductor devices are cut out of it.

. Application

Specially doped silicon is widely used as a material for the manufacture of semiconductor devices (transistors, thermistors, power rectifiers, controllable diodes - thyristors; solar photocells used in spaceships, etc.). Since silicon is transparent to rays with a wavelength of 1 to 9 microns, it is used in infrared optics.

Silicon has diverse and ever-expanding applications. In metallurgy, silicon is used to remove oxygen dissolved in molten metals (deoxidation). Silicon is integral part a large number of iron alloys and non-ferrous metals. Usually, silicon gives alloys increased resistance to corrosion, improves their casting properties and increases mechanical strength; however, at higher levels, silicon can cause brittleness. The most important are iron, copper and aluminum alloys containing silicon. An increasing amount of silicon is used for the synthesis of organosilicon compounds and silicides. Silica and many silicates (clays, feldspars, micas, talcs, etc.) are processed by the glass, cement, ceramics, electrical engineering, and other branches of industry.

Siliconization, surface or volume saturation of a material with silicon. It is produced by processing the material in silicon vapor formed at high temperature above the silicon filling, or in a gaseous medium containing chlorosilanes, which are reduced by hydrogen, for example, by the reaction

l 4+ 2H2 = Si + 4HC1.

It is mainly used as a means of protecting refractory metals (W, Mo, Ta, Ti, etc.) from oxidation. Resistance to oxidation is due to the formation of dense diffusion "self-healing" silicide coatings (WSi 2, MoSi 2and etc.). Wide application finds siliconized graphite.

. Connections

Silicides

Silicides (from lat. Silicium - silicon), chemical compounds of silicon with metals and some non-metals. Silicides according to the type of chemical bond can be divided into three main groups: ionic-covalent, covalent and metal-like. Ionic-covalent silicides are formed by alkali (with the exception of sodium and potassium) and alkaline earth metals, as well as metals of the copper and zinc subgroups; covalent - boron, carbon, nitrogen, oxygen, phosphorus, sulfur, they are also called borides, carbides, silicon nitrides), etc.; metal-like - transition metals.

Silicides are obtained by fusing or sintering a powder mixture of Si and the corresponding metal: by heating metal oxides with Si, SiC, SiO 2and silicates, natural or synthetic (sometimes mixed with carbon); interaction of metal with a mixture of SiCl 4and H 2; electrolysis of melts consisting of K 2SiF 6and oxide of the corresponding metal. Covalent and metal-like silicides are refractory, resistant to oxidation, the action of mineral acids and various aggressive gases. Silicides are used in the composition of heat-resistant metal-ceramic composite materials for aviation and rocket technology. MoSi 2is used for the production of heaters for resistance furnaces operating in air at temperatures up to 1600 °C. FeSi 2, Fe 3Si 2, Fe 2Si is a constituent of ferrosilicon used for deoxidation and alloying of steels. Silicon carbide is one of the semiconductor materials.

siliconized graphite

Siliconized graphite, graphite saturated with silicon. It is produced by processing porous graphite in silicon filling at 1800-2200 ° C (in this case, silicon vapor is deposited in the pores). Consists of a graphite base, silicon carbide and free silicon. Combines graphite's inherent high heat resistance and strength at elevated temperatures with density, gas tightness, high oxidation resistance at temperatures up to 1750 ° C and erosion resistance. It is used for lining high-temperature furnaces, in metal pouring devices, in heating elements, for the manufacture of parts for aviation and space technology operating at high temperatures and erosion

Silal

Silal (from Latin Silicium - silicon and English alloy - alloy), heat-resistant cast iron with a high silicon content (5-6%). Relatively cheap cast parts are made from silal, operating at high temperatures (800-900 ° C), for example, open-hearth furnace doors, grates, parts of steam boilers.

Silumin

Silumin (from lat. Silicium - silicon and Aluminum - aluminum), common name a group of cast alloys based on aluminum containing silicon (4-13%, in some grades up to 23%). Depending on the desired combination of technological and operational properties, silumin is alloyed with Cu, Mn, Mg, sometimes Zn, Ti, Be and other metals. Silumins have high casting and rather high mechanical properties, yielding, however, in terms of mechanical properties to casting alloys based on the Al-Cu system. The advantages of silumins include their increased corrosion resistance in humid and marine atmospheres. Silumins are used in the manufacture of parts complex configuration, mainly in the automotive and aircraft industries.

Silicomanganese

Silicomanganese is a ferroalloy whose main components are silicon and manganese; smelted in ore-thermal furnaces by a coal-reduction process. Silicomanganese with 10-26% Si (the rest is Mn, Fe and impurities), obtained from manganese ore, manganese slag and quartzite, is used in steelmaking as a deoxidizer and alloying additive, as well as for smelting ferromanganese with a reduced carbon content by a silicothermic process. Silicomanganese with 28-30% Si (raw material for which is a specially obtained high-manganese low-phosphorus slag) is used in the production of metallic manganese.

Silicochrome

Silicochrome, ferrosilicochrome, ferroalloy, the main components of which are silicon and chromium; smelted in an ore-thermal furnace by a coal-reduction process from quartzite and granular pig ferrochrome or chromium ore. Silicochrome with 10-46% Si (the rest Cr, Fe and impurities) is used in the smelting of low-alloy steel, as well as for the production of ferrochrome with a reduced carbon content by the silicothermic process. Silicochromium with 43-55% Si is used in the production of carbon-free ferrochromium and in the smelting of stainless steel.

Silchrome (from Latin Silicium - silicon and Chromium - chromium), the general name for a group of heat-resistant and heat-resistant steels alloyed with Cr (5-14%) and Si (1-3%). Depending on the required level of performance properties, silchrome is additionally alloyed with Mo (up to 0.9%) or Al (up to 1.8%). Silchromes are resistant to oxidation in air and in sulfur-containing environments up to 850-950 °C; they are mainly used for the manufacture of valves for internal combustion engines, as well as parts for boiler installations, grates, etc. With increased mechanical loads, parts made of silchrome reliably operate for a long time at temperatures up to 600-800 ° C.

Silicon halides

Silicon halides, compounds of silicon with halogens. Silicon halides of the following types (X-halogen) are known: SiX 4, SiH n X 4-n (halosilanes), Si n X 2n+2 and mixed halides, such as SiClBr 3. Under normal conditions SiF 4- gas, SiCl 4and SiBr 4- liquids (tmelt - 68.8 and 5°C), SiI 4- solid body (tnl 124°C). SiX connections 4easily hydrolyzed:

SiX 4+2H 2O=SiO 2+4HX;

smoke in the air due to the formation of very small particles SiO 2; silicon tetrafluoride reacts differently:

SiF 4+2H 2O=SiO 2+2H 2SiF 6

Chlorosilanes (SiH n X 4-n ), e.g. SiHCl 3(obtained by the action of gaseous HCl on Si), under the action of water they form polymer compounds with a strong siloxane chain Si-O-Si. Being highly reactive, chlorosilanes serve as starting materials for the production of organosilicon compounds. Si type connections n X2 n+2 containing chains of Si atoms, with X - chlorine, give a series, including Si 6Cl 14(tnl 320°С); other halogens form only Si 2X 6. Compounds of types (SiX 2)n and (SiX) n . SiX molecules 2and SiX exist at high temperature in the form of a gas and upon rapid cooling (liquid nitrogen) form solid polymeric substances that are insoluble in common organic solvents.

Silicon tetrachloride SiCl4 is used in the production of lubricating oils, electrical insulation, heat transfer fluids, water-repellent liquids, etc. silicon silicate quartz crystal

Silicon carbide

Silicon carbide, carborundum, SiC, silicon-carbon compound; one of the most important carbides used in engineering. In its pure form, silicon carbide is a colorless crystal with a diamond luster; green or blue-black technical product. Silicon carbide exists in two main crystalline modifications - hexagonal (a-SiC) and cubic (b-SiC), and hexagonal is a "giant molecule" built on the principle of a kind of structure-directed polymerization of simple molecules. Layers of carbon and silicon atoms in a-SiC are placed relative to each other in different ways, forming many structural types. The b-SiC transition to a-SiC occurs at a temperature of 2100–2300°C (the reverse transition is usually not observed). Silicon carbide is refractory (melts with decomposition at 2830°C), has exceptionally high hardness (microhardness 33400 MN/m ² or 3.34 tf/mm ² ), second only to diamond and boron carbide B4 C; fragile; density 3.2 g/cm ³ . Silicon carbide is stable in various chemical environments, including at high temperatures.

Silicon carbide is produced in electric furnaces at 2000-2200°C from a mixture of quartz sand (51-55%), coke (35-40%) with the addition of NaCI (I-5%) and sawdust (5-10%). Due to its high hardness, chemical resistance and wear resistance, silicon carbide is widely used as an abrasive material (when grinding), for cutting hard materials, pointing tools, as well as for the manufacture of various parts of chemical and metallurgical equipment operating in difficult conditions of high temperatures. Silicon carbide doped with various impurities is used in semiconductor technology, especially at elevated temperatures. It is interesting to use silicon carbide in electrical engineering - for the manufacture of heaters for high-temperature electric resistance furnaces (silite rods), lightning arresters for electric current transmission lines, non-linear resistances, as part of electrical insulating devices, etc.

silicon dioxide

Silicon dioxide (silica), SiO 2, crystals. The most common mineral is quartz; regular sand is also silicon dioxide. Used in the production of glass, porcelain, faience, concrete, brick, ceramics, as a rubber filler, adsorbent in chromatography, electronics, acousto-optics, etc. Silica minerals, a number of mineral species, which are polymorphic modifications of silicon dioxide; stable at certain temperature intervals depending on pressure.

The basis of the crystalline structure of silica is a three-dimensional framework built from tetrahedra (5104) connected through common oxygen. However, the symmetry of their location, packing density, and mutual orientation are different, which is reflected in the symmetry of the crystals of individual minerals and their physical properties. An exception is stishovite, whose structure is based on octahedrons (SiO 6), forming a rutile-like structure. All silicas (with the exception of some varieties of quartz) are usually colorless. The hardness on the mineralogical scale is different: from 5.5 (a-tridymite) to 8-8.5 (stishovite).

Silica is usually found in the form of very small grains, cryptocrystalline fibrous (a-cristobalite, so-called lyussatite), and sometimes spheroidal formations. Less often - in the form of crystals of a tabular or lamellar appearance (tridymite), octahedral, dipyramidal (a- and b-cristobalite), fine needles (coesite, stishovite). Most Silica (except quartz) is very rare and unstable under conditions of the surface zones of the earth's crust. High temperature modifications of SiO 2- b-tridymite, b-cristobalite - are formed in small voids of young effusive rocks (dacites, basalts, liparites, etc.). Low-temperature a-cristobalite, along with a-tridymite, is one of the components of agate, chalcedony, and opal; deposited from hot aqueous solutions, sometimes from colloidal SiO 2. Stishovite and coesite are found in the sandstones of the Devil's Canyon meteor crater in Arizona (USA), where they were formed by quartz at instantaneous ultrahigh pressure and with an increase in temperature during a meteorite fall. Also found in nature: quartz glass (the so-called leshatelierite), which is formed as a result of the melting of quartz sand from a lightning strike, and melanophlogite - in the form of small cubic crystals and crusts (pseudomorphoses consisting of opal-like and chalcedony-like quartz), grown on native sulfur in the deposits of Sicily (Italy). Whale is not found in nature.

Quartz (German: Quarz), mineral; under the name of quartz, two crystalline modifications of silicon dioxide SiO are known 2: hexagonal quartz (or a-quartz), stable at a pressure of 1 atm (or 100 kN/m ² ) in the temperature range 870-573 °C, and trigonal (b-quartz), stable at temperatures below 573 °C. b-quartz is most widely found in nature. It crystallizes in the trigonal trapezohedron class of the trigonal system. The frame-type crystal structure is built of silicon-oxygen tetrahedra arranged helically (with the right or left-hand screw) with respect to the main axis of the crystal. Depending on this, right and left structural-morphological forms of crystals are distinguished, which differ externally in the symmetry of the arrangement of some faces (for example, a trapezohedron, etc.). The absence of planes and a center of symmetry in quartz crystals determines the presence of piezoelectric and pyroelectric properties.

Most often, quartz crystals have an elongated prismatic appearance with the predominant development of hexagonal prism faces and two rhombohedrons (crystal head). More rarely, crystals take the form of a pseudohexagonal dipyramid. Outwardly regular quartz crystals are usually complexly twinned, most often forming twin areas according to the so-called. Brazilian or Dauphinean laws. The latter arise not only during the growth of crystals, but also as a result of internal structural rearrangement during thermal a - b transitions accompanied by compression, as well as during mechanical deformations. The color of quartz crystals, grains, aggregates is the most diverse: colorless, milky white or gray quartz is most common. Transparent or translucent beautifully colored crystals are called especially: colorless, transparent - rock crystal; purple - amethyst; smoky - rauchtopaz; black - morion; golden yellow - citrine. Different colors are usually due to structural defects when replacing Si 4+on Fe 3+or Al 3+with simultaneous entry into the lattice Na 1+, Li 1+or (OH) 1-. There are also complexly colored quartz due to microinclusions of foreign minerals: green prase - inclusions of microcrystals of actinolite or chlorite; golden shimmering aventurine - inclusions of mica or hematite, etc. Cryptocrystalline varieties of quartz - agate and chalcedony - consist of the finest fibrous formations. Quartz is optically uniaxial, positive. Refractive indices (for daylight l=589.3): ne=1.553; no=1.544. Transparent to ultraviolet and partially infrared rays. When a plane-polarized light beam is transmitted in the direction of the optical axis, the left quartz crystals rotate the polarization plane to the left, and the right ones to the right. In the visible part of the spectrum, the value of the rotation angle (per 1 mm quartz plate thickness) varies from 32.7 (for l 486 nm) to 13.9° (728 nm). Meaning permittivity(eij), piezoelectric modulus (djj) and elastic coefficients (Sij) are as follows (at room temperature): e11 = 4.58; e33 = 4.70; d11 \u003d -6.76 * 10-8; d14 \u003d 2.56 * 10-8; S11 = 1.279; S12 = - 0.159; S13 = -0.110; S14 = -0.446; S33 = 0.956; S44 = 1.978. Linear expansion coefficients are: perpendicular to the 3rd order axis 13.4*10 -6and parallel to the axis 8*10 -6. The heat of transformation b - a K. is 2.5 kcal / mol (10.45 kJ / mol). Hardness on a mineralogical scale 7; density 2650 kg/m ³ . It melts at a temperature of 1710 ° C and solidifies upon cooling in the so-called. quartz glass. Fused quartz is a good insulator; the resistance of a cube with an edge of 1 cm at 18 ° C is 5 * 10 18ohm/cm, linear expansion coefficient 0.57*10 -6cm/°C. An economically advantageous technology has been developed for growing single crystals of synthetic oxygen, which is obtained from aqueous solutions of SiO2 at elevated pressures and temperatures (hydrothermal synthesis). Synthetic crystals have stable piezoelectric properties, radiation resistance, high optical uniformity, and other valuable technical properties.

Natural quartz is a very widespread mineral, it is an essential component of many rocks, as well as mineral deposits of the most diverse genesis. The most important quartz materials for industry are quartz sands, quartzites and crystalline single-crystal quartz. The latter is rare and highly valued. The main deposits of quartz crystals are in the Urals, in the Pamirs, in the basin of the river. Aldan; abroad - deposits in Brazil and the Malagasy Republic. Quartz sands are an important raw material for the ceramic and glass industries. Quartz single crystals are used in radio engineering (piezoelectric frequency stabilizers, filters, resonators, piezoelectric plates in ultrasonic installations, etc.); in optical instrumentation (prisms for spectrographs, monochromators, lenses for ultraviolet optics, etc.). Fused quartz is used to make special chemical glassware. K. is also used to obtain chemically pure silicon. Transparent, beautifully colored varieties of quartz are semi-precious stones and are widely used in jewelry.

Quartz glass, a one-component silicate glass obtained by melting natural silica varieties - rock crystal, vein quartz and quartz sand, as well as synthetic silicon dioxide. There are two types of industrial quartz glass: transparent (optical and technical) and opaque. Opacity to quartz glass gives a large number of small gas bubbles distributed in it (with a diameter of 0.03 to 0.3 microns) that scatter light. Optical transparent quartz glass, obtained by melting rock crystal, is completely homogeneous, does not contain visible gas bubbles; has the lowest refractive index among silicate glasses (nD = 1.4584) and the highest light transmission, especially for ultraviolet rays. Quartz glass is characterized by high thermal and chemical resistance; softening point K. s. 1400 °C. Quartz glass is a good dielectric, specific electrical conductivity at 20 °С-10 -14 - 10-16ohm -1m -1, tangent of the angle dielectric losses at a temperature of 20 ° C and a frequency of 106 Hz - 0.0025-0.0006. Quartz glass is used for the manufacture of laboratory glassware, crucibles, optical instruments, insulators (especially for high temperatures), products resistant to temperature fluctuations.

Silanes

Silanes (from lat. Silicium - silicon), compounds of silicon with hydrogen of the general formula Si n H2 n+2 . Silanes up to octasilane Si 8H 18. At room temperature, the first two silicon compounds are monosilane SiH 4and disilane Si 2H 6- gaseous, the rest - volatile liquids. All silicon compounds have an unpleasant odor and are poisonous. Silanes are much less stable than alkanes; they spontaneously ignite in air, for example

Si 2H 6+7O 2=4SiO2 +6H 2O.

Water decomposes:

3H 8+6H 2O=3SiO2 +10H 2

Silanes do not occur in nature. In the laboratory, by the action of dilute acids on magnesium silicide, a mixture of various minerals is obtained, which is strongly cooled and separated (by fractional distillation in the complete absence of air).

Silicic acids

Silicic acids, derivatives of silicic anhydride SiO 2; very weak acids, slightly soluble in water. Pure metasilicic acid H 2SiO 3(more precisely, its polymeric form H 8Si 4O 12) and H 2Si 2O 5. Amorphous silicon dioxide (amorphous silica) in aqueous solution (solubility about 100 mg in 1 l) forms predominantly orthosilicic acid H 4SiO 4. In supersaturated solutions obtained by various methods, silicic acids change with the formation of colloidal particles (molar mass up to 1500), on the surface of which there are OH groups. Educated so. the sol, depending on the pH, can be stable (pH about 2) or can aggregate, turning into a gel (pH 5-6). Stable, highly concentrated silicic acid sols containing special substances - stabilizers, are used in the production of paper, in the textile industry, and for water purification. Fluorosilicic acid, H 2SiF 6, a strong inorganic acid. Exists only in aqueous solution; in free form decomposes into silicon tetrafluoride SiF 4and hydrogen fluoride HF. It is used as a strong disinfectant, but mainly for the production of silicic acid salts - silicofluorides.

silicates

Silicates, salts of silicon acids. The most widely distributed in the earth's crust (80% by weight); more than 500 minerals are known, among them - gems such as emerald, beryl, aquamarine. Silicates - the basis of cements, ceramics, enamels, silicate glass; raw materials in the production of many metals, adhesives, paints, etc.; materials of radio electronics, etc. Silicofluorides, fluorosilicates, salts of fluorosilicic acid H 2SiF 6. When heated, they decompose, for example

6= CaF2 + SiF 4

Na, K, Rb, Cs and Ba salts are sparingly soluble in water and form characteristic crystals, which is used in quantitative and microchemical analysis. Sodium silicofluoride Na 2SiF 6(in particular, in the production of acid-resistant cements, enamels, etc.). A significant proportion of Na 2SiF 6processed into NaF. Get Na 2SiF 6containing SiF 4waste from superphosphate plants. Mg, Zn and Al silicofluorides (the technical name of fluates) are highly soluble in water and are used to make building stone waterproof. All silicates (as well as H 2SiF6 ) are poisonous.

Application

Fig.1 Right and left quartz.

Fig.2 Silica minerals.

Fig.3 Quartz (structure)

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Many modern technological devices and devices were created due to the unique properties of substances found in nature. Mankind, by experimentation and careful study of the elements around us, is constantly modernizing its own inventions - this process is called technical progress. It is based on elementary, accessible to everyone things that surround us in Everyday life. For example, sand: what can be surprising and unusual in it? Scientists were able to isolate silicon from it - a chemical element without which there would be no computer technology. The scope of its application is diverse and constantly expanding. This is achieved due to the unique properties of the silicon atom, its structure and the possibility of compounds with other simple substances.

Characteristic

In the one developed by D. I. Mendeleev, silicon is designated by the symbol Si. It belongs to non-metals, is located in the main fourth group of the third period, has atomic number 14. Its proximity to carbon is not accidental: in many respects their properties are comparable. It does not occur in nature in its pure form, as it is an active element and has fairly strong bonds with oxygen. The main substance is silica, which is an oxide, and silicates (sand). At the same time, silicon (its natural compounds) is one of the most common chemical elements on Earth. In terms of mass fraction of content, it ranks second after oxygen (more than 28%). The top layer of the earth's crust contains silicon dioxide (this is quartz), various types of clays and sand. The second most common group is its silicates. At a depth of about 35 km from the surface, there are layers of granite and basalt deposits, which include siliceous compounds. The percentage of content in the earth's core has not yet been calculated, but the layers of the mantle closest to the surface (up to 900 km) contain silicates. As part of sea ​​water silicon concentration is 3 mg/l, 40% consists of its compounds. The expanses of space that mankind has studied to date contain this chemical element in large quantities. For example, meteorites that approached the Earth at a distance accessible to researchers showed that they consist of 20% silicon. There is a possibility of the formation of life based on this element in our galaxy.

Research process

The history of the discovery of the chemical element silicon has several stages. Many substances systematized by Mendeleev have been used by mankind for centuries. At the same time, the elements were in their natural form, i.e. in compounds that were not subjected to chemical processing, and all their properties were not known to people. In the process of studying all the features of the substance, new directions of use appeared for it. The properties of silicon have not been fully studied to date - this element, with a fairly wide and varied range of applications, leaves room for new discoveries for future generations of scientists. Modern technologies significantly speed up this process. In the 19th century, many famous chemists tried to obtain pure silicon. For the first time, L. Tenar and J. Gay-Lussac managed to do this in 1811, but the discovery of the element belongs to J. Berzelius, who was able not only to isolate the substance, but also to describe it. A Swedish chemist obtained silicon in 1823 using potassium metal and potassium salt. The reaction took place with a catalyst in the form of high temperature. The obtained simple gray-brown substance was amorphous silicon. The crystalline pure element was obtained in 1855 by St. Clair Deville. The complexity of isolation is directly related to the high strength of atomic bonds. In both cases, the chemical reaction is aimed at the process of purification from impurities, while the amorphous and crystalline models have different properties.

Silicon pronunciation of the chemical element

The first name of the resulting powder - kisel - was proposed by Berzelius. In the UK and the USA, silicon is still called nothing more than silicon (Silicium) or silicone (Silicon). The term comes from the Latin "flint" (or "stone"), and in most cases it is tied to the concept of "earth" due to its wide distribution in nature. Russian pronunciation given chemical It varies, it all depends on the source. It was called silica (Zakharov used this term in 1810), sicily (1824, Dvigubsky, Solovyov), silica (1825, Strakhov), and only in 1834 did the Russian chemist German Ivanovich Hess introduce the name that is still used today. in most sources - silicon. In it is denoted by the symbol Si. How is the chemical element silicon read? Many scientists in English-speaking countries pronounce its name as "si" or use the word "silicone". From here comes the world-famous name of the valley, which is a research and production site for computer technology. The Russian-speaking population calls the element silicon (from the ancient Greek word for "rock, mountain").

Finding in nature: deposits

Entire mountain systems are composed of silicon compounds, which are not found in their pure form, because all known minerals are dioxides or silicates (aluminosilicates). Amazingly beautiful stones are used by people as an ornamental material - these are opals, amethysts, quartzes various types, jasper, chalcedony, agate, rock crystal, carnelian and many others. They were formed due to the inclusion of various substances in the composition of silicon, which determined their density, structure, color and direction of use. The whole inorganic world can be associated with this chemical element, which in natural environment forms strong bonds with metals and non-metals (zinc, magnesium, calcium, manganese, titanium, etc.). Compared to other substances, silicon is readily available for mining on an industrial scale: it is found in most types of ores and minerals. Therefore, actively developed deposits are tied to available energy sources rather than to territorial accumulations of matter. Quartzites and quartz sands are found in all countries of the world. The largest manufacturers and suppliers of silicon are: China, Norway, France, USA (West Virginia, Ohio, Alabama, New York), Australia, South Africa, Canada, Brazil. All manufacturers use various ways, which depend on the type of manufactured products (technical, semiconductor, high-frequency silicon). A chemical element, additionally enriched or, conversely, purified from all types of impurities, has individual properties on which its further use depends. This also applies to this substance. The structure of silicon determines the scope of its application.

Usage history

Very often, due to the similarity of names, people confuse silicon and flint, but these concepts are not identical. Let's bring clarity. As already mentioned, silicon in its pure form does not occur in nature, which cannot be said about its compounds (the same silica). The main minerals and rocks formed by the dioxide of the substance we are considering are sand (river and quartz), quartz and quartzites, and flint. Everyone must have heard about the latter, because it is given great importance in the history of human development. The first tools created by people during the Stone Age are associated with this stone. Its sharp edges, formed when breaking off from the main rock, greatly facilitated the work of ancient housewives, and the possibility of sharpening - hunters and fishermen. Flint did not have the strength of metal products, but failed tools were easy to replace with new ones. Its use as a flint and steel continued for many centuries - until the invention of alternative sources.

As for modern realities, the properties of silicon make it possible to use the substance for interior decoration or the creation of ceramic dishes, while, in addition to a beautiful aesthetic appearance, it has many excellent functional qualities. A separate direction of its application is associated with the invention of glass about 3000 years ago. This event made it possible to create mirrors, dishes, mosaic stained-glass windows from compounds containing silicon. The formula of the initial substance was supplemented with the necessary components, which made it possible to give the product the required color and influenced the strength of the glass. Works of art of amazing beauty and variety were made by man from minerals and stones containing silicon. The healing properties of this element were described by ancient scientists and have been used throughout the history of mankind. They laid out wells for drinking water, pantries for storing food, used both in everyday life and in medicine. The powder obtained as a result of grinding was applied to wounds. Particular attention was paid to water, which was infused in dishes made from compounds containing silicon. The chemical element interacted with its composition, which made it possible to destroy a number of pathogenic bacteria and microorganisms. And this is far from all the industries where the substance we are considering is very, very in demand. The structure of silicon determines its versatility.

Properties

For a more detailed acquaintance with the features of a substance, it must be considered taking into account all possible properties. The plan for characterizing the chemical element of silicon includes physical properties, electrophysical indicators, the study of compounds, reactions and conditions for their passage, etc. Silicon in crystalline form has a dark gray color with a metallic sheen. The face-centered cubic lattice is similar to the carbon one (diamond), but due to the longer bonds, it is not so strong. Heating up to 800 ° C makes it plastic, in other cases it remains brittle. The physical properties of silicon make this substance truly unique: it is transparent to infrared radiation. Melting point - 1410 0 C, boiling point - 2600 0 C, density under normal conditions - 2330 kg / m 3. The thermal conductivity is not constant, for various samples it is taken at an approximate value of 25 0 C. The properties of the silicon atom make it possible to use it as a semiconductor. This area of ​​application is most in demand in modern world. The magnitude of the electrical conductivity is influenced by the composition of silicon and the elements that are in combination with it. So, for increased electronic conductivity, antimony, arsenic, phosphorus are used, for perforated - aluminum, gallium, boron, indium. When creating devices with silicon as a conductor, surface treatment with a certain agent is used, which affects the operation of the device.

The properties of silicon as an excellent conductor are widely used in modern instrumentation. Its use in the production of complex equipment (for example, modern computing devices, computers) is especially relevant.

Silicon: characteristics of a chemical element

In most cases, silicon is tetravalent, there are also bonds in which it can have a value of +2. Under normal conditions, it is inactive, has strong compounds, and at room temperature can react only with fluorine, which is in a gaseous state of aggregation. This is due to the effect of blocking the surface with a dioxide film, which is observed when interacting with ambient oxygen or water. To stimulate reactions, a catalyst must be used: raising the temperature is ideal for a substance such as silicon. The chemical element interacts with oxygen at 400-500 0 C, as a result, the dioxide film increases, and the oxidation process takes place. When the temperature rises to 50 0 C, a reaction with bromine, chlorine, iodine is observed, resulting in the formation of volatile tetrahalides. Silicon does not interact with acids, with the exception of a mixture of hydrofluoric and nitric acids, while any alkali in a heated state is a solvent. Silicon hydrogens are formed only by the decomposition of silicides; it does not react with hydrogen. Compounds with boron and carbon are distinguished by the greatest strength and chemical passivity. High resistance to alkalis and acids has a connection with nitrogen, which occurs at temperatures above 1000 0 C. Silicides are obtained by reaction with metals, and in this case, the valency shown by silicon depends on the additional element. The formula of the substance formed with the participation of the transition metal is resistant to acids. The structure of the silicon atom directly affects its properties and ability to interact with other elements. The process of formation of bonds in nature and when exposed to matter (in laboratory, industrial conditions) differs significantly. The structure of silicon suggests its chemical activity.

Structure

Silicon has its own characteristics. The charge of the nucleus is +14, which corresponds to the serial number in the periodic system. Number of charged particles: protons - 14; electrons - 14; neutrons - 14. The scheme of the structure of the silicon atom has the following form: Si +14) 2) 8) 4. There are 4 electrons at the last (external) level, which determines the degree of oxidation with the “+” or “-” sign. Silicon oxide has the formula SiO 2 (valence 4+), the volatile hydrogen compound is SiH 4 (valency -4). The large volume of the silicon atom makes it possible in some compounds to have a coordination number of 6, for example, when combined with fluorine. Molar mass - 28, atomic radius - 132 pm, electron shell configuration: 1S 2 2S 2 2P 6 3S 2 3P 2.

Application

Surface or fully doped silicon is used as a semiconductor in the creation of many, including high-precision, devices (for example, solar photocells, transistors, current rectifiers, etc.). Ultra-pure silicon is used to create solar panels(energy). The single-crystal type is used to make mirrors and a gas laser. From silicon compounds, glass, ceramic tiles, dishes, porcelain, faience are obtained. It is difficult to describe the variety of types of goods received, their operation takes place at the household level, in art and science, and in production. The resulting cement serves as a raw material for the creation of building mixtures and bricks, finishing materials. The distribution of oils, based on lubricants, can significantly reduce the friction force in the moving parts of many mechanisms. Silicides are widely used in industry due to their unique properties in the field of resistance to aggressive media (acids, temperatures). Their electrical, nuclear and chemical characteristics are taken into account by specialists in complex industries, and the structure of the silicon atom also plays an important role.

We have listed the most knowledge-intensive and advanced areas of application to date. The most common, commercial silicon produced in large volumes is used in a number of areas:

1. As a raw material for the production of a purer substance.
2. For alloying alloys in the metallurgical industry: the presence of silicon increases refractoriness, increases corrosion resistance and mechanical strength (with an excess of this element, the alloy may be too brittle).
3. As a deoxidizer to remove excess oxygen from metal.
4. Raw materials for the production of silanes (silicon compounds with organic substances).
5. For the production of hydrogen from an alloy of silicon with iron.
6. Manufacturing of solar panels.

The value of this substance is also great for the normal functioning of the human body. The structure of silicon, its properties are decisive in this case. At the same time, an excess or lack of it leads to serious diseases.

In the human body

Medicine has long used silicon as a bactericidal and antiseptic agent. But with all the benefits of external use, this element must be constantly renewed in the human body. A normal level of its content will improve life in general. In case of its deficiency, more than 70 trace elements and vitamins will not be absorbed by the body, which will significantly reduce resistance to a number of diseases. The highest percentage of silicon is observed in bones, skin, tendons. It plays the role of a structural element that maintains strength and gives elasticity. All skeletal hard tissues are formed by its compounds. As a result of recent studies, silicon content was found in the kidneys, pancreas and connective tissues. The role of these organs in the functioning of the body is quite large, so a decrease in its content will have a detrimental effect on many basic indicators of life support. The body should receive 1 gram of silicon per day with food and water - this will help to avoid possible diseases, such as inflammation of the skin, softening of the bones, the formation of stones in the liver, kidneys, visual impairment, hair and nails, atherosclerosis. At sufficient level the content of this element increases immunity, normalizes metabolic processes, improves the absorption of many elements necessary for human health. The largest amount of silicon is in cereals, radish, buckwheat. Silicon water will bring significant benefits. To determine the amount and frequency of its use, it is better to consult a specialist.

CPU? Sand? What associations do you have with this word? Or maybe Silicon Valley?
Be that as it may, we encounter silicon every day, and if you are interested in knowing what Si is and what it is eaten with, please under cat.

Introduction

Silicium

History reference

Silicon is very common in nature in the composition of ordinary sand.

Distribution of silicon in nature

Physical properties of Silicon

Chemical Properties of Silicon

Obtaining Silicon

Silicon of technical purity (95-98%) is obtained in an electric arc by the reduction of silica SiO2 between graphite electrodes. In connection with the development of semiconductor technology, methods have been developed for obtaining pure and extra pure silicon. This requires a preliminary synthesis of the purest initial silicon compounds, from which silicon is extracted by reduction or thermal decomposition.
Polycrystalline silicon ("polysilicon") - the purest form of industrially produced silicon - a semi-finished product obtained by cleaning technical silicon by chloride and fluoride methods and used for the production of mono- and multi-crystalline silicon.
Traditionally, polycrystalline silicon is obtained from technical silicon by converting it into volatile silanes (monosilane, chlorosilanes, fluorosilanes), followed by separation of the resulting silanes, distillation purification of the selected silane, and reduction of the silane to metallic silicon.
Pure semiconductor silicon is obtained in two forms: polycrystalline(reduction of SiCl4 or SiHCl3 with zinc or hydrogen, thermal decomposition of SiI4 and SiH4) and monocrystalline(crucible-free zone melting and "pulling" of a single crystal from molten silicon - the Czochralski method).

Here you can see the process of growing silicon using the Czochralski method.

Czochralski method- a method of growing crystals by pulling them up from the free surface of a large volume of the melt with the initiation of the onset of crystallization by bringing a seed crystal (or several crystals) of a given structure and crystallographic orientation into contact with the free surface of the melt.

Silicon Application

Ultrapure silicon and its product

Silicon in the body

Conclusion