Where is silicon used? Silicon: properties and uses for medicinal purposes. Silicon as a building material

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MINISTRY OF BRANCH OF RUSSIA

federal state budgetary educational institution

higher professional education

"St. Petersburg State Technological Institute

(technical university) "(SPbSTI (TU))

CHAIR HNT MET

UGS 240100.62

SPECIALTY Chemical Technology

DIRECTION Chemistry of substances and materials

DISCIPLINE Introduction to the specialty

ON THE TOPIC: Silicon, its properties and application in modern electronics

Performed by a 1st year student, group 131

Zhukovskaya Ekaterina Olesevna

Yezhovsky Yuri Konstantinovich

Saint Petersburg 2013

Introduction

1. Silicon

2. History

3. Origin of the name

4. Being in nature

5. Receiving

6. Physical properties

7. Electrophysical properties

8. Chemical properties

10. Application

List of references

Introduction

Silicon is one of the important elements. Vernadsky wrote his famous work: "No organism can exist without silicon" (1944). In a handbook on chemistry for 9th grade schoolchildren (Minsk publishing house: "Slovo", 1977), in the "Silicon" section, it says: "... silicon is an extremely important semiconductor material used for the manufacture of microelectronic devices -" microcircuits ". used in the production of solar batteries, converts solar energy into electrical energy. Among 104 elements of the periodic table, silicon has a special role. It is a piezoelectric element. It can convert one type of energy into another. Mechanical into electrical, light into heat, etc. " It is silicon that underlies energy-information exchange in space and on Earth. From the table chemical composition It can be seen that the most widespread element in this world is oxygen - 47%, the second place is occupied by silicon - 29.5%, and the content of other elements is much less.

The most widespread semiconductor in the production of electronic components is silicon, since its reserves on the planet are practically unlimited.

1. Silicon

Silicon is an element of the main subgroup of the fourth group of the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 14. It is designated by the symbol Si (Latin Silicium).

Appearance of a simple substance

In amorphous form - brown powder, in crystalline form - dark gray, slightly shiny.

Atom properties

Name, symbol, number: Silicon / Silicium (Si), 14

Atomic mass (molar mass) 28,0856 amu (g / mol)

Electronic configuration: 3s2 3p2, conn. 3s 3p3 (hybridization)

Atomic radius 132 nm

Chemical properties

Covalent radius 111 nm

Ion radius 42 (+ 4e) 271 (-4e) nm

Electronegativity 1.90 (Pauling scale)

Electrode potential 0

Oxidation states: +4, +2, 0, -4

Ionization energy (first electron) 786.0 (8.15) kJ / mol (eV)

Thermodynamic properties of a simple substance

Density (at normal level) 2.33 g / cm3

Melting point 1414.85 ° C (1688 K)

Evaporating temperature 2349.85 ° C (2623 K)

Heat of fusion 50.6 kJ / mol

Heat of vaporization 383 kJ / mol

Molar heat capacity 20.16 J / (K mol)

Molar volume 12.1 cm3 / mol

The crystal lattice of a simple substance

Lattice structure: cubic, diamond

Lattice parameters: 5.4307 E

Debye temperature 625 K

Other characteristics

Thermal conductivity (300 K) 149 W / (m K)

2. History

Natural silicon compounds or silicon (English Silicon, French and German Silicium) - silicon dioxide (silica) - have been known for a long time. The ancients knew well rock crystal, or quartz, as well as precious stones, which are quartz painted in different colors (amethyst, smoky quartz, chalcedony, chrysoprase, topaz, onyx, etc.) Elementary silicon was obtained only in the 19th century, although attempts Scheele and Lavoisier, Dzvi (with the help of the Voltaic pillar), Gay-Lussac and Tenard (chemically) undertook to decompose silica. Vercelius, trying to decompose silica, heated it in a mixture with iron powder and coal to 1500 ° C and obtained ferrosilicon. Only in 1823 r. when studying compounds of hydrofluoric acid, including SiF4, he obtained free amorphous silicon ("silica radical") by the interaction of vapors of silicon fluoride and potassium. Saint Clair-Deville obtained crystalline silicon in 1855.

3. Origin of the name

The name silicium or kizel (Kiesel, flint) was proposed by Berzelius. Earlier, Thomson proposed the name silicone (Silicon), adopted in England and the USA, by analogy with harrows (Boron) and carbon (Carbon). The word silicon (Silicium) comes from silica (silica); the ending "a" was adopted in the 18th and 19th centuries. to designate lands (Silica, Aluminia, Thoria, Terbia, Glucina, Cadmia, etc.). In turn, the word silica is associated with lat. Silex (strong, flint).

The Russian name for silicon comes from the Old Slavic words flint (the name of the stone), kremyk, strong, kresmen, kresati (hitting a belt with an iron to get sparks), etc. In Russian chemical literature of the early 19th century. there are names of silica (Zakharov, 1810), silicium (Soloviev, Dvigubsky, 1824), flint (Strakhov, 1825), siliceousness (Iovskiy, 1827), silica and silicon (Hess, 1831).

4. Being in nature

Most often in nature, silicon is found in the form of silica - compounds based on silicon dioxide (IV) SiO2 (about 12% of the mass of the earth's crust). The main minerals and rocks formed by silicon dioxide are sand (river and quartz), quartz and quartzite, flint, feldspars. The second most common group of silicon compounds in nature are silicates and aluminosilicates.

Isolated facts of finding pure silicon in a native state are noted.

Silicon is found in most minerals and ores. There are necessary deposits of quartzite and quartz sand in many countries of the world. However, to get more quality product or to increase profitability indicators, it is more profitable to use raw materials with a maximum silicon content (up to 99% SiO2). Such rich deposits are extremely rare and have been actively and for a long time used by the competing glass industry all over the world. The latter, however, is reluctant to process raw materials even with minimal iron contamination, but in the production of ferroalloys it is not very critical. In general, throughout the world, the provision of silicon production with raw materials is considered high, and the corresponding share of costs in its cost is insignificant (less than 10%).

silicon amorphous atom

5. Receiving

“Free silicon can be obtained by calcining fine white sand with magnesium, which is silicon dioxide:

This forms a brown powder amorphous silicon».

In industry, technical grade silicon is obtained by reducing the SiO2 melt with coke at a temperature of about 1800 ° C in shaft-type ore-thermal furnaces. The purity of the silicon obtained in this way can reach 99.9% (the main impurities are carbon, metals).

Further purification of silicon from impurities is possible.

Cleaning under laboratory conditions can be carried out by preliminary preparation of magnesium silicide Mg2Si. Further, gaseous monosilane SiH4 is obtained from magnesium silicide using hydrochloric or acetic acids. Monosilane is purified by rectification, sorption and other methods, and then decomposed into silicon and hydrogen at a temperature of about 1000 ° C.

The purification of silicon on an industrial scale is carried out by direct chlorination of silicon. In this case, compounds of the composition SiCl4 and SiCl3H are formed. These chlorides are purified from impurities in various ways (usually by distillation and disproportionation) and, at the final stage, are reduced with pure hydrogen at temperatures from 900 to 1100 ° C.

Cheaper, cleaner and more efficient industrial silicon purification technologies are being developed. For 2010, these include silicon purification technologies using fluorine (instead of chlorine); technologies for distillation of silicon monoxide; technologies based on the etching of impurities concentrating on intercrystalline boundaries.

The method of obtaining silicon in its pure form was developed by Nikolai Nikolaevich Beketov.

In Russia, technical silicon is produced by OK Rusal at factories in Kamensk-Uralsky (Sverdlovsk Region) and Shelekhov (Irkutsk Region); Silicon refined using chloride technology is produced by the Nitol Solar group at the plant in Usolye-Sibirskoye.

6. Physical properties

Crystal structure of silicon

The crystal lattice of silicon is cubic, face-centered, of the diamond type, parameter a \u003d 0.54307 nm (at high pressures, other polymorphic modifications of silicon have been obtained), but due to the longer bond length between Si - Si atoms compared to the length links C - C the hardness of silicon is significantly less than that of diamond. Silicon is fragile, only when heated above 800 ° C does it become a ductile substance. Interestingly, silicon is transparent to infrared radiation from a wavelength of 1.1 μm. Self concentration charge carriers - 5.81 · 1015 m? 3 (for a temperature of 300 K).

7. Electrophysical properties

Elemental silicon in monocrystalline form is an indirect-gap semiconductor. The band gap at room temperature is 1.12 eV, and at T \u003d 0 K is 1.21 eV. The concentration of intrinsic charge carriers in silicon under normal conditions is about 1.5 × 1010 cm? 3.

The impurities contained in it have a great influence on the electrophysical properties of crystalline silicon. To obtain silicon crystals with hole conductivity, atoms of elements of the III group, such as boron, aluminum, gallium, indium, are introduced into silicon. To obtain silicon crystals with electronic conductivity, atoms are introduced into silicon elements of the Vth groups such as phosphorus, arsenic, antimony.

When creating electronic devices based on silicon, the surface layer of the material is mainly involved (up to tens of microns), so the quality of the crystal surface can have a significant effect on the electrical properties of silicon and, accordingly, on the properties of the finished device. Some devices use surface modification techniques, such as surface treatment of silicon with various chemical agents.

Dielectric constant: 12

Electron mobility: 1200-1450 cm2 / (V s).

Hole mobility: 500 cm2 / (V s).

Forbidden band 1.205-2.84 10 4 T

Electron lifetime: 5 ns - 10 ms

Free path of an electron: about 0.1 cm

Hole free path: about 0.02 - 0.06 cm

All values \u200b\u200bare based on normal conditions.

8. Chemical properties

Like carbon atoms, silicon atoms are characterized by the state of sp3-hybridization of orbitals. In connection with hybridization, pure crystalline silicon forms a diamond-like lattice in which silicon is tetravalent. In compounds, silicon usually also manifests itself as a tetravalent element with an oxidation state of +4 or −4. There are bivalent silicon compounds, for example, silicon oxide (II) - SiO.

Under normal conditions, silicon is chemically inactive and reacts actively only with gaseous fluorine, thus forming volatile silicon tetrafluoride SiF4. This "inactivity" of silicon is associated with the passivation of the surface with a nanosized layer of silicon dioxide, which is immediately formed in the presence of oxygen, air, or water (water vapor).

When heated to temperatures above 400-500 ° C, silicon reacts with oxygen to form SiO2 dioxide, the process is accompanied by an increase in the thickness of the dioxide layer on the surface, the rate of the oxidation process is limited by the diffusion of atomic oxygen through the dioxide film.

When heated to temperatures above 400-500 ° C, silicon reacts with chlorine, bromine and iodine to form the corresponding readily volatile tetrahalides SiHal4 and, possibly, halides of a more complex composition.

Silicon does not directly react with hydrogen, silicon compounds with hydrogen - silanes with the general formula SinH2n + 2 - are obtained indirectly. Monosilane SiH4 (it is often called simply silane) is released when metal silicides react with acid solutions, for example:

The silane SiH4 formed in this reaction contains an impurity of other silanes, in particular, disilane Si2H6 and trisilane Si3H8, which contain a chain of silicon atoms linked by single bonds (--Si - Si - Si--).

With nitrogen, silicon at a temperature of about 1000 ° C forms Si3N4 nitride, with boron - thermally and chemically resistant borides SiB3, SiB6 and SiB12.

At temperatures above 1000 ° C, you can get a silicon compound and its closest analogue according to the periodic table - carbon - silicon carbide SiC (carborundum), which is characterized by high hardness and low chemical activity. Carborundum is widely used as an abrasive. At the same time, interestingly, a silicon melt (1415 ° C) can contact carbon for a long time in the form of large pieces of densely sintered fine-grained graphite by isostatic pressing, practically not dissolving or interacting with the latter.

The underlying elements of the 4th group (Ge, Sn, Pb) are infinitely soluble in silicon, like most other metals. When silicon is heated with metals, silicides can form. Silicides can be divided into two groups: ionic-covalent (silicides of alkali, alkaline earth metals and magnesium such as Ca2Si, Mg2Si, etc.) and metal-like (transition metal silicides). Silicides of active metals decompose under the action of acids, silicides of transition metals are chemically stable and do not decompose under the action of acids. Metal-like silicides have high melting points (up to 2000 ° C). Most often, metal-like silicides are formed with the compositions MeSi, Me3Si2, Me2Si3, Me5Si3, and MeSi2. Metal-like silicides are chemically inert and resistant to oxygen even at high temperatures.

It should be especially noted that silicon forms a eutectic mixture with iron, which allows sintering (fusing) these materials to form ferrosilicon ceramics at temperatures noticeably lower than the melting temperatures of iron and silicon.

When SiO2 is reduced with silicon at temperatures above 1200 ° C, silicon oxide (II) - SiO is formed. This process is constantly observed in the production of silicon crystals using the Czochralski, directional crystallization methods, because they use containers of silicon dioxide as the least polluting material for silicon.

Silicon is characterized by the formation of organosilicon compounds in which silicon atoms are linked into long chains due to bridging oxygen atoms --O--, and to each silicon atom, in addition to two O atoms, two more organic radicals are attached R1 and R2 \u003d CH3, C2H5, C6H5, CH2CH2CF3, etc.

A mixture of hydrofluoric and nitric acids is most widely used for etching silicon. Some special etchants include the addition of chromic anhydride and other substances. During etching, the acid etching solution quickly heats up to the boiling point, while the etching rate increases many times.

Si + 2HNO3 \u003d SiO2 + NO + NO2 + H2O

SiO2 + 4HF \u003d SiF4 + 2H2O

3SiF4 + 3H2O \u003d 2H2SiF6 + vH2SiO3

For etching silicon, aqueous solutions of alkalis can be used. Etching of silicon in alkaline solutions begins at a solution temperature of more than 60 ° C.

Si + 2KOH + H2O \u003d K2SiO3 + 2H2 ^

K2SiO3 + 2H2O-H2SiO3 + 2KOH

9. Silicon in the human body

Si is an essential trace element in the human body. The main role of silicon in the human body is participation in a chemical reaction, the essence of which is to bond the subunits of the body's fibrous tissues (collagen and elastin) together, which gives them strength and elasticity. He is also directly involved in the process of bone mineralization. It is found in many organs and tissues, such as the lungs, adrenal glands, trachea, bones and ligaments, which indicates its increased biocompatibility. Another important function of silicon is to maintain normal metabolism in the body. More precisely - if silicon is not enough, then about 70 other elements are not absorbed by the body. Silicon creates colloidal systems that absorb harmful microorganisms and viruses, thus purifying the body. A person needs at least 10 milligrams of silicon daily. Silicon can be delivered to the body in two ways: water containing silicon, and eating certain plants. With food, up to 1 g of Si is supplied to the human body daily, a lack of this element can lead to weakening of bone tissue and the development of infectious diseases.

Widely known medicinal properties silicon water. Silicon water is a simple means of replenishing the concentration of this vital substance in the body. One of the most silicon-rich natural sources is blue, medicinal, food clay.

10. Application

Application in medicine:

In medicine, silicon is used in silicones, high-molecular inert compounds that are used as coatings for medical technology. In recent years, dietary supplements and medications, enriched with silicon, used for the prevention and treatment of osteoporosis, atherosclerosis, diseases of the nails, hair and skin.

Application in construction and light industry:

Silicon compounds are widely used both in the field of high technology and in everyday life. Silica and natural silicates are precursors in the production of glass, ceramics, porcelain, cement, concrete products, abrasive materials, etc. Silicon dioxide is used in combination with a number of ingredients in the manufacture of fiber optic cables. Mica and asbestos are used as electrical and thermal insulation materials.

Polymer-modified sprayed concrete is an economical material for tunneling. Silicones prevent damage from moisture and harmful chemicals. Roofing coatings based on silicone dispersions allow for bold design ideas and have impressive technical characteristics. Copolymer dispersions provide the necessary balance of adhesion and flexibility for high quality HVAC sealants.

Silicones are great for finishing leather and textiles, protecting the end product and optimizing manufacturing processes.

Various silicone compounds are suitable as antifoam agents for all types of cleaning agents.

Silicon-based dispersions provide efficient absorption and are used in the manufacture of absorbents.

Silicones can be found under the hood, in transmissions, electronics and electrical systems, in car interiors, or in body seams. Even at high temperatures, silicon protects against aggressive substances, or acts as a bridge, vibration damper, conductor or insulator. All this is possible only due to the fact that silicon-containing polymers have an amazingly wide range of useful properties.

Adhesives and sealants are critical products in many key industries. Silicon is used in a variety of industrial applications, from paper, packaging, wood and flooring adhesives to the automotive and wind energy sectors.

Heavy industry applications:

The use of silicon as the basis for a whole range of semiconductors - from solar batteries to computer processors - is "heard", therefore this material is the basis of most "high technologies". The tonnage of world production of high-purity semiconductor silicon has been growing for several decades at an average rate of up to 20% per year and has no analogues among other rare metals.

Silicon of high purity is used in semiconductor technology, and of technical purity (96-99% Si) - in ferrous and nonferrous metallurgy to obtain non-ferrous alloys (silumin, etc.), alloying (silicon steels and alloys used in electrical equipment) and deoxidation steel and alloys (oxygen removal), silicide production, etc.

In industry, technical grade silicon is obtained by reducing the SiO2 melt with coke at a temperature of about 1800 degrees Celsius in shaft-type ore-thermal furnaces. The purity of the silicon obtained in this way can reach 99.9% (the main impurities are carbon, metals).

The use of pure silicon and its compounds in the chemical industry is growing at an outstripping rate (about 8% of growth per year). In recent decades, developed countries have rapidly developed technologies for the production of a range of silicone (organosilicon) materials used in the production of plastics, paints and varnishes, lubricants, etc.

However, most of the applications of silicon in the world (almost 80%) remain traditional - it is a master alloy in the production of a range of special steels (electrical, heat-resistant) and various alloys (silumins, etc.). A significant part of silicon and its alloys is used in ferrous metallurgy as a very effective deoxidizer for steels.

Ferroalloys and other silicon alloys are mainly used in ferrous metallurgy. They are cheaper and more technologically advanced to use, and the iron content (and in some cases aluminum) is not so critical. The composition of electrical steels, as a rule, contains 3.8-4.2% silicon, therefore, only these steel-making industries in the world consume more than 0.5 million tons of silicon per year as a master alloy. Another significant application of ferrosilicon (including also silicomanganese and complex compositions) is in effective and relatively inexpensive deoxidizers for steels.

In non-ferrous metallurgy (and chemical industry), metallic magnesium is used more widely. It finds the greatest application as a master alloy of hardened aluminum (silumins) and magnesium alloys.

Silicon finds some application (as silicon carbide and complex compositions) in the production of abrasive and carbide products and tools.

Applications in energy, electrical and electronics:

The dual properties of silicon, such as electrical conductivity and insulating qualities, as well as flexibility, allow silicon to be used across the entire product line, such as lighting fixtures, capacitors, insulators, and chips and dielectrics. Thus, silicon insulates against all kinds of external effects such as dirt, moisture, radiation or heat.

In consumer electronics and measurement sensors, silicones provide the reliability and safety of electrical and sensitive electronic equipment. They are used in the automotive industry, light industry, semiconductor industry and optoelectronics, as well as in measuring instruments and control and lighting technology.

In resistors and capacitors, methyl silicone resins provide an effective coating to prevent fires in the event of power surges.

In insulators, cables and transformers, pyrogenic silica exhibits excellent thermal insulation over a wide temperature range, from room temperature to over 1000 ° C.

Modern and promising information technologies (computers, electronics, telecommunications, etc.) are based and will be based on the use of semiconductor silicon. The most in demand now are semi-finished products - precision (polished) silicon wafers up to 300 mm in diameter, on the basis of which the most modern microcircuits are created (element sizes up to 0.065 microns).

The use of silicon in the aviation industry is due to its ability to generate energy through high-quality solar panels, as well as serve as a substrate in complex microcircuits and protect ship hulls from external influences.

Silicon (c-Si) in its various forms (crystalline, polycrystalline, amorphous) at the present time and in the foreseeable future will remain the main material of microelectronics. This is due to a number of its unique physical and chemical properties, of which the following can be distinguished:

1. Silicon as a starting material is available and cheap, and the technology of its production, purification, processing and alloying is well developed, which provides a high degree of crystallographic perfection of the fabricated structures. It should be specially emphasized that silicon is much superior to steel in this indicator.

2. Silicon has good mechanical properties. In terms of Young's modulus, silicon approaches stainless steel and is much superior to quartz and various glasses. In terms of hardness, silicon is close to quartz and is almost twice as hard as iron. Silicon single crystals have a yield point that is three times that of stainless steel. However, upon deformation, it collapses without visible changes in size, whereas metals usually undergo plastic deformation. The reasons for the destruction of silicon are associated with structural defects of the crystal lattice located on the surface of silicon single crystals.

The semiconductor industry successfully solves the problem of high-quality surface treatment of silicon, so that often silicon mechanical components (for example, elastic elements in pressure sensors) are stronger than steel.

The microelectronic technology for the manufacture of silicon devices is based on the use of thin layers created by ion implantation or thermal diffusion of dopant atoms, which, in combination with the methods of vacuum deposition of metals on a silicon surface, turned out to be very convenient for the purpose of miniaturizing products.

Silicon microelectronic devices are manufactured using group technology. This means that all manufacturing processes are carried out for an entire silicon wafer, which contains several hundred individual crystals ("chips"). And only at the last stage of manufacturing, the plate is divided into crystals, which are then used in the assembly of individual devices, which ultimately sharply reduces their cost.

To reproduce the sizes and shapes of structures of silicon devices, the photolithography method is used, which ensures high manufacturing accuracy.

For the production of sensors, the ability of silicon to respond to various types of influences is especially important: mechanical, thermal, magnetic, chemical and electrical. The versatility of silicon application helps to reduce the cost of sensors and unify their manufacturing technology. In sensors, silicon serves as a transducer, the main purpose of which is to convert the measured physical or chemical effect into an electrical signal. Silicon functions in sensors are much broader than in conventional integrated circuits. This determines some specific features of the technology for manufacturing silicon sensitive elements.

List of references

1. Chemical encyclopedia: in 5 vols. / Editorial board: I.L. Knunyants (chief editor). - Moscow: Soviet Encyclopedia, 1990 .-- T. 2. - P. 508 .-- 671 p. - 100,000 copies

2. J.P. Riley and Skirrow G. Chemical Oceanography V. 1, 1965

3. Metallic silicon in ijolites of the Goryachegorsk massif, Petrology of ordinary chondrites

4. Glinka N.L. General chemistry. - 24th ed., Rev. - L .: Chemistry, 1985 .-- S. 492 .-- 702 p.

5. R Smith., Semiconductors: Per. from English. - M .: Mir, 1982 .-- 560 p., Ill.

6. Pakhomova T.B., Alexandrova E.A., Simanova S.A. Silicon: A Study Guide. - SPb .: SPbGTI (TU), 2003 .-- 24p.

7. Zi S., Physics of semiconductor devices: In 2 books. Book. 1. Per. from English. - M .: Mir, 1984 .-- 456 p., Ill.

8. Koledov LA Technologies and designs of microcircuits, microprocessors and microassemblies: a textbook // 2nd ed., Rev. and add. - SPb.: Publishing house "Lan", 2007.

9. Samsonov. G.V. Silicides and their use in technology. - Kiev, Publishing House of the Academy of Sciences of the Ukrainian SSR, 1959 .-- 204 p. from Fig.

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Ministry of General and Vocational Education

Novosibirsk State Technical

university.

RGR on Organic Chemistry.

"SILICON"

Faculty: EM

Group: EM-012

Completed by: Danilov I.V.

Teacher: Shevnitsyna LV

Novosibirsk, 2001

Silicon (Latin Silicium), Si, chemical element of group IV periodic

mendeleev's systems; atomic number 14, atomic mass 28.086. In nature

element is represented by three stable isotopes: 28Si (92.27%), 29Si

(4.68%) and 30Si (3.05%).

Silicon in living organisms.

Silicon in the body is in the form of various compounds involved

mainly in the formation of hard skeletal parts and tissues. Special

a lot of K. can accumulate some marine plants (for example, diatoms

algae) and animals (for example, flint sponges, radiolarians),

during the dying off at the bottom of the ocean, forming powerful deposits of silicon dioxide. IN

cold seas and lakes are dominated by biogenic silts enriched with K., in

tropical seas - lime mud with a low K content.

many plants K. accumulate grasses, sedges, palms, and horsetails. In vertebrates

the greatest quantities of K. are found in dense connective tissue, kidneys,

pancreas. The daily human diet contains up to 1 g K. When

human and causes disease -Silicosis (from Latin silex -

flint), a human disease caused by prolonged inhalation of dust,

diseases. It is found among workers of mining, porcelain,

metallurgical, machine-building industries. S. - the most

unfavorable disease from the group of pneumoconiosis; more than

with other diseases, the joining of the tuberculous process is noted

(so-called silicotuberculosis) and other complications.

Discovery history and use.

Historical reference. K. compounds, widespread on earth, were

known to man from the Stone Age. Using stone tools for labor

and the hunt went on for several millennia. The use of K. compounds,

related to their processing - glass making - started around 3000

years BC e. (in Ancient Egypt). The earliest known compound K. is

siO2 dioxide (silica). In the 18th century. silica was considered a simple body and

attributed to "lands" (which is reflected in its name). Complexity of the composition

silica was established by I. Ya. Berzelius. Free silicon for the first time

was obtained in 1811 by the French scientist J. Gay-Lussac and O. Thénard. IN

1825 Swedish mineralogist and chemist Jens Jacob Berzelius received an amorphous

silicon. Brown amorphous silicon powder was obtained by reducing

potassium metal of gaseous silicon tetrafluoride:

SiF4 + 4K \u003d Si + 4KF

Later, a crystalline form of silicon was obtained. By recrystallization

silicon from molten metals were obtained gray solid, but

fragile crystals with a metallic luster. Russian names for eliment

silicon was introduced into use by G.I.Hess in 1834.

Distribution in nature.

After oxygen, silicon is the most abundant element (27.6%) on earth.

It is an element that is found in most minerals and rocks,

constituting the hard shell of the earth's crust. In the earth's crust K. plays the same

a primary role as carbon in the animal and plant world. For

geochemistry of K. is extremely important for its strong bond with oxygen. Most

widespread silicon compounds - silicon oxide SiO2 and

silicic acid derivatives called silicates. Silicon (IV) oxide

occurs as a quartz mineral (silica, flint). In nature from this

whole mountains are piled up. There are very large ones, weighing up to 40 tons,

quartz crystals. Ordinary sand consists of fine quartz contaminated with

various impurities. The annual global consumption of sand reaches 300

million tons.

Of the silicates, aluminosilicates (kaolin

Al2O3 * 2SiO2 * 2H2O, asbestos CaO * 3MgO * 4SiO2, orthoclase K2O * Al2O3 * 6SiO2, etc.).

If in addition to silicon and aluminum oxides, the mineral contains oxides

sodium, potassium or calcium, the mineral is called feldspar (white

mica, etc.). Feldspars account for about half of the known

the nature of silicates. Rock granite and gneiss include quartz, mica,

feldspar.

In the flora and fauna, silicon is included in insignificant amounts

explains the increased strength of the stems of these plants. Ciliate shells,

sponge bodies, bird eggs and feathers, animal hair, hair, vitreous

eyes also contain silicon.

Analysis of lunar soil samples delivered by ships showed

the presence of silicon oxide in a quantity of more than 40 percent. As part of stone

meteorites, the silicon content reaches 20 percent.

Atomic structure and basic chemical and physical. Holy Island.

K. forms crystals, dark gray with a metallic luster,

a cubic face-centered lattice of the diamond type with a period a \u003d 5.431E,

with a density of 2.33 g / cm3. At very high pressures, a new (

apparently hexagonal) modification with a density of 2.55 g / cm3. K. melts

at 1417 ° C, boils at 2600 ° C. Specific heat (at 20-100 ° С) 800

j / (kgChK), or 0.191 cal / (gChrad); thermal conductivity even for the cleanest

samples is not constant and is in the range (25 ° C) 84-126 W / (mChK), or

0.20-0.30 cal / (cmChsecChgrad). Temperature coefficient of linear expansion

2.33X10-6 K-1; below 120K becomes negative. K. is transparent to

long-wave infrared rays; refractive index (for l \u003d 6 microns) 3.42;

dielectric constant 11.7. K. diamagnetic, atomic magnetic

susceptibility -0.13 × 10-6. Hardness K. Mohs 7.0, Brinell 2.4

Gn / m2 (240 kgf / mm2), elastic modulus 109 Gn / m2 (10890 kgf / mm2),

the compressibility factor is 0.325X10-6 cm2 / kg. K. brittle material; noticeable

plastic deformation begins at temperatures above 800 ° C.

K. is a semiconductor that is finding increasing use. Electrical

properties of K. very strongly depend on impurities. Own specific volume

electrical resistance K. at room temperature is assumed to be

2.3X103 ohmChm (2.3Ch105 ohmChm).

Semiconductor K. with p-type conductivity (additives B, Al, In, or Ga) and n-

type (additives P, Bi, As or Sb) has significantly lower resistance.

The energy 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 K. in the periodic system of Mendeleev 14

electrons of the atom K. are distributed over three shells: in the first (from the nucleus) 2

electron, in the second 8, in the third (valence) 4; configuration electronic

shells 1s22s22p63s23p2. Consecutive ionization potentials (eV):

8.149; 16.34; 33.46 and 45.13. Atomic radius 1.33Е, covalent radius

1.17E, ionic radii Si4 + 0.39E, Si4- 1.98E.

In compounds, K. (similar to carbon) is 4-valency. However, unlike

carbon, K. along with the coordination number 4 exhibits a coordination

number 6, which is explained by the large volume of its atom (an example of such

compounds are fluorosilicon containing group 2-).

The chemical bond between an atom and other atoms is usually carried out at the expense of

hybrid sp3 orbitals, but it is also possible to involve two of its five

(vacant) 3d-orbitals, especially when K. is six-coordinated.

With a small electronegativity value of 1.8 (versus 2.5 for

carbon; 3.0 for nitrogen, etc.), K. in compounds with non-metals

is electrically positive, and these compounds are polar in nature. Big

binding energy with oxygen Si-O, equal to 464 kJ / mol (111 kcal / mol),

determines the endurance 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 is not characteristic of K.

between Si atoms. In air K. due to the formation of a protective oxide

films are stable even at elevated temperatures. Oxidizes in oxygen

starting at 400 ° C, forming silicon dioxide SiO2. Also known monoxide

SiO, stable at high temperatures as a gas; as a result of the sharp

cooling, a solid product can be obtained that easily decomposes into

a fine mixture of Si and SiO2. K. is resistant to acids and dissolves only in

mixtures of nitric and hydrofluoric acids; dissolves easily in hot

alkali solutions with hydrogen evolution. K. reacts with fluorine when

room temperature, with the rest of the halogens - when heated with

the formation of compounds of the general formula SiX4 (see Silicon halides).

Hydrogen does not directly react with K., and silicas (silanes)

get the decomposition of silicides (see below). Known silicas from SiH4

up to Si8H18 (similar in composition to saturated hydrocarbons). K. forms 2

groups of oxygen-containing silanes - siloxanes and siloxenes. With nitrogen K.

reacts at temperatures above 1000 ° C. Of great practical importance is

nitride Si3N4, not oxidizing in air even at 1200 ° C, resistant to

in relation to acids (except nitric) and alkalis, as well as to molten

metals and slags, making it a valuable material for chemical

industry, for the production of refractories, etc. High hardness, and

also thermal and chemical resistance are distinguished by compounds K. with

carbon (silicon carbide SiC) and boron (SiB3, SiB6, SiB12). When

heating K. reacts (in the presence of metal catalysts,

for example copper) with organochlorine compounds (for example, with CH3Cl) with

the formation of organohalosilanes [for example, Si (CH3) 3CI], which serve to

synthesis of numerous organosilicon compounds.

Receiving.

The simplest and most convenient laboratory method for producing silicon is

reduction of silicon oxide SiO2 at high temperatures with metals -

restorers. Due to the stability of silicon oxide for reduction

use such active reducing agents as magnesium and aluminum:

3SiO2 + 4Al \u003d 3Si + 2Al2O3

Upon reduction with metallic aluminum, crystalline

silicon. Method for the reduction of metals from their metal oxides

aluminum was discovered by the Russian physicochemist NN Beketov in 1865. When

reduction of silicon oxide with aluminum, the released heat is not enough for

melting reaction products - silicon and aluminum oxide, which

melts at 2050 C. To lower the melting point of the reaction products in

sulfur and excess aluminum are added to the reaction mixture. The reaction forms

low-melting aluminum sulfide:

2Al + 3S \u003d Al2S3

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

To. Technical purity (95-98%) is obtained in an electric arc

reduction of silica SiO2 between graphite electrodes.

In connection with the development of semiconductor technology, methods for obtaining

pure and especially pure K. This requires a preliminary synthesis of the purest

initial compounds K., from which K. is extracted by reduction or

thermal decomposition.

Pure semiconductor silicon is obtained in two forms: polycrystalline

(reduction of SiCI4 or SiHCl3 with zinc or hydrogen, thermal

decomposition of Sil4 and SiH4) and monocrystalline (crucible-free zone melting

and by "pulling" a single crystal from molten K. — the Czochralski method).

Silicon tetrachloride is obtained by chlorination of commercial silicon.

The oldest method for the decomposition of silicon tetrachloride is the method

the outstanding Russian chemist academician N.N. Beketov. This method can be

represented by the equation:

SiCl4 + Zn \u003d Si + 2ZnCl2.

Here vapors of silicon tetrachloride boiling at 57.6 ° C,

interact with zinc vapor.

Currently, silicon tetrachloride is reduced with hydrogen. Reaction

proceeds according to the equation:

SiCl4 + 2H2 \u003d Si + 4HCl.

Silicon is obtained in powder form. The iodide method is also used

obtaining silicon, similar to the previously described iodide method of obtaining

pure titanium.

To obtain pure silicon, it is purified from impurities by zone melting.

similarly to how pure titanium is obtained.

For a variety of semiconductor devices,

semiconductor materials obtained in the form of single crystals, since in

polycrystalline material, uncontrolled changes occur

electrical properties.

When rotating single crystals, the Czochralski method is used, which consists of

in the following: a rod is lowered into the molten material, at the end of which

there is a crystal of this material; he serves as the embryo 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. Of

it is cut out by the wafers used in semiconductor devices.

Application.

Specially alloyed carbon is widely used as a material for manufacturing

semiconductor devices (transistors, thermistors, power rectifiers

current, controlled diodes - thyristors; solar photovoltaic cells used in

spaceships, etc.). Since K. is transparent to rays with a length

waves from 1 to 9 microns, it is used in infrared optics (see also Quartz).

K. has various and ever expanding fields of application. IN

metallurgy K. is used to remove dissolved in molten

oxygen metals (deoxidation). K. is an integral part of a large

the number of alloys of iron and non-ferrous metals. Usually K. gives alloys

increased resistance to corrosion, improves their casting properties and

increases mechanical strength; however, with a greater content of it, K. can

cause fragility. The most important are iron, copper and aluminum

organosilicon compounds and silicides. Silica and many silicates

(clays, feldspars, micas, talc, etc.) are processed by glass,

cement, ceramic, electrical and other industries.

Siliconizing, surface or volumetric saturation of the material with silicon.

It is produced by processing the material in silicon vapor formed at high

temperature above the silicon backfill, or in a gas environment containing

chlorosilanes reduced by hydrogen (for example, by the reaction SiCI4 + 2H2

Si + 4HC1). It is mainly used as a means of protection for refractory

metals (W, Mo, Ta, Ti, etc.) from oxidation. Oxidation resistance

due to the formation at S. of dense diffusion

"Self-healing" silicide coatings (WSi2, MoSi2, etc.). Wide

siliconized graphite is used.

Connections.

Silicides.

Silicides (from Lat. Silicium - silicon), chemical compounds of silicon with

metals and some non-metals. C. by the type of chemical bond can be

subdivided into three main groups: ionic-covalent, covalent and

metal-like. Ionic-covalent S. are formed by alkaline (with the exception of

sodium and potassium) and alkaline earth metals, as well as metals of subgroups

copper and zinc; covalent - boron, carbon, nitrogen, oxygen, phosphorus,

sulfur, they are also called borides, carbides, silicon nitrides), etc.;

metal-like - transition metals.

Received by fusing or sintering a powder mixture of Si and

the corresponding metal: by heating metal oxides with Si, SiC, SiO2 and

natural or synthetic silicates (sometimes mixed with carbon);

the interaction of the metal with a mixture of SiCl4 and H2; electrolysis of melts,

consisting of K2SiF6 and the oxide of the corresponding metal. Covalent and

metal-like S. refractory, resistant to oxidation, the action of mineral

acids and various aggressive gases. S. are used as part of heat-resistant

metal-ceramic composite materials for aviation and missile

technology. MoSi2 is used for the production of resistance furnace heaters,

working in air at temperatures up to 1600 ° С. FeSi2, Fe3Si2, Fe2Si

are part of ferrosilicon used for deoxidation and alloying

steels. Silicon carbide is one of the semiconductor materials.

Siliconized graphite

Siliconized graphite, silicon saturated graphite. Produced by processing

porous graphite in a silicon backfill at 1800-2200 ° C (while vapors

silicon is deposited in the pores). Composed of graphite base, silicon carbide

and free silicon. Combines high temperature resistance characteristic of graphite

and strength at elevated temperatures with density, gas tightness,

high resistance to oxidation at temperatures up to 1750 ° C and erosion

persistence. It is used for lining high-temperature furnaces, in

devices for casting metal, in heating elements, for

manufacturing of parts for aviation and space technology, working in

high temperature and erosion conditions

Silal (from Latin Silicium - silicon and English alloy - alloy), heat-resistant cast iron

with a high silicon content (5-6%). 2 varieties are produced in the USSR

S. - with lamellar and nodular graphite. From S., relatively

cheap cast parts operating at high temperatures (800-900

° С), for example the doors of open-hearth furnaces, grates, parts of steam boilers.

Silumin (from Latin Silicium - silicon and Aluminum - aluminum), common name

a group of aluminum-based casting alloys containing silicon (4-13%, in

some brands up to 23%). Depending on the desired combination

technological and operational properties of C. are alloyed with Cu, Mn, Mg, sometimes

Zn, Ti, Be and other metals. C. have high casting and sufficient

high mechanical properties, inferior, however, in mechanical

properties of casting alloys based on the Al - Cu system. To the merits of S.

their increased corrosion resistance in wet and marine

atmospheres. S. are used in the manufacture of parts of complex configuration,

mainly in the auto and aircraft industry. In the USSR, S. of grades AL2 is produced,

AL4, AL9, etc.

Silicomanganese

Silicomanganese is a ferroalloy whose main components are silicon and manganese;

is smelted in ore-thermal furnaces by a carbon-reduction process. FROM.

with 10-26% Si (the rest is Mn, Fe and impurities), obtained from manganese ore,

manganese slag and quartzite, used in steelmaking as

deoxidizer and alloying additive, as well as for smelting ferromanganese with

reduced carbon content by silicothermal process. C. with 28-30% Si

(the raw material for which is specially obtained high-manganese

low-phosphorous slag) is used in the production of metallic manganese.

Silicochrom

Silicochromium, ferrosilicochromium, ferroalloy, the main components of which are

silicon and chromium; smelted in an ore-thermal furnace with a carbon-reducing

a process of quartzite and granulated conversion ferrochrome or

chrome ore. C. with 10-46% Si (the rest is Cr, Fe and impurities) is used for

smelting low-alloy steel, as well as for obtaining ferrochrome with

reduced carbon content by silicothermal process. C. with 43-55% Si

used in the production of carbon-free ferrochrome and in smelting

of stainless steel.

Silchrome

Silchrome (from Latin Silicium - silicon and Chromium - chromium), common name

groups of heat-resistant and heat-resistant steels alloyed with Cr (5-14%) and Si

(1-3%). Depending on the required level of operational properties, C.

additionally alloyed with Mo (up to 0.9%) or Al (up to 1.8%). C. resistant against

oxidation in air and in sulfur-containing media up to 850-950 ° С; apply

mainly for the manufacture of valves for internal combustion engines,

as well as details of boiler installations, grates, etc.

mechanical loads, parts made of S. work reliably for a long

term at temperatures up to 600-800 ° C. In the USSR, S. of grades 4Х9С2,

4X10C2M, etc.

Silicon halides

Silicon halides, silicon compounds with halogens. Known K. g.

of the following types (X-halogen): SiX4, SiHnX4-n (halogenosilanes), SinX2n + 2 and

mixed halides such as SiClBr3. Under normal conditions, SiF4 is a gas,

SiCl4 and SiBr4 - liquids (tm - 68.8 and 5 ° С), SiI4 - solid (tnl

124 ° C). SiX4 compounds are easily hydrolyzed: SiX4 + 2H2O \u003d SiO2 + 4HX;

smoke in air due to the formation of very small particles of SiO2;

silicon tetrafluoride reacts differently: 3SiF4 + 2H2O \u003d SiO2 + 2H2SiF6. Chlorosilanes

(SiHnX4-n), for example SiHCl3 (obtained by the action of gaseous HCl on Si),

under the action of water form polymer compounds with a strong siloxane

chain Si-O-Si. Highly reactive, chlorosilanes

serve as starting materials for the production of organosilicon compounds.

Compounds of the SinX2n + 2 type containing chains of Si atoms, at X - chlorine, give

a series, including Si6Cl14 (tnl 320 ° C); the rest of the halogens form only Si2X6.

Compounds of types (SiX2) n and (SiX) n were obtained. SiX2 and SiX molecules

exist at high temperatures in the form of gas and with sharp cooling

(liquid nitrogen) form solid polymer substances, 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 carbide.

Silicon carbide, carborundum, SiC, silicon-carbon compound; one of

the most important carbides used in technology. In its pure form K. to. - colorless

crystal with diamond luster; technical product green or blue-black

colors. To. To. Exists in two main crystalline modifications -

hexagonal (a-SiC) and cubic (b-SiC), with the hexagonal being

"Giant molecule" built on the principle of a kind of structural

directed polymerization of simple molecules. Layers of carbon atoms and

silicon in a-SiC are placed relative to each other in different ways, forming many

structural types. The transition from b-SiC to a-SiC occurs at a temperature

2100-2300 ° C (the reverse transition is usually not observed). K. k. Refractory

(melts with decomposition at 2830 ° C), has an extremely high hardness

(microhardness 33400 Mn / m2 or 3.34 tf / mm2), second only to diamond and boron

carbide B4C; fragile; density 3.2 g / cm3. K. to. Is stable in various

chemical environments, including at high temperatures.

K. to. Is obtained in electric furnaces at 2000-2200 ° C from a mixture of quartz sand

(51-55%), coke (35-40%) with addition of NaCl (I-5%) and sawdust (5-10%).

Due to its high hardness, chemical resistance and wear resistance, K.

because it is widely used as an abrasive material (when grinding), for cutting

hard materials, tool points, as well as for the manufacture of various

parts of chemical and metallurgical equipment operating in complex

high temperature conditions. K. to., Doped with various impurities,

used in semiconductor technology, especially with increased

temperatures. It is interesting to use K. to. In electrical engineering - for

manufacture of heaters for high-temperature electric resistance furnaces

(sieve rods), lightning arresters for electrical transmission lines

current, nonlinear resistances, as part of electrical insulating devices, etc.

Silicon Dioxide

SILICON DIOXIDE (silica), SiO2, crystals. Most common

mineral - quartz; ordinary sand is also silicon dioxide. Used in

production of glass, porcelain, earthenware, concrete, brick, ceramics, as

rubber filler, adsorbent in chromatography, electronics, acousto-optics

and other Silica minerals, a number of mineral species, which are

polymorphic modifications of silicon dioxide; stable under certain

temperature intervals depending on pressure.

| Name | | System | Pressure, | Tempera- | Density |

| Mineral | | | am * | | Th, |

| | | | | round, ° С | kg / m "|

| b-cristobali | | cubic | 1 | 1728-147 | 2190 |

| t | | | | 0 | |

| b-tridymite | | Hexagonal | 1 | 1470-870 | 2220 |

| | | naya | | | |

| a-quartz | | hexagonal | 1 | 870-573 | 2530 |

| | | naya | | | |

| b-quartz | | trigonal | 1 | below 573 | 2650 |

| b1-tridymite | | hexagonal | 1 | 163-117 | approx. |

| | | naya | | | 2260 |

| a-tridymite | metastable | rhombic | 1 | below 117 | approx. |

| | th | | | | 2260 |

| a-cristobali | | Tetragonal | 1 | below 200 | 2320 |

| t | | naya | | | |

| Coesite | Metastable | monoclinic | 35 thousand | 1700-500 | 2930 |

| | e at low | | | | |

| | temp- | | | | |

| | raturah and | | | | |

| | pressures | | | | |

| Stishovit | | tetragonal | 100-180 | 1400-600 | 4350 |

| | | naya | thousand | | |

| Kitit | | tetragonal | 350-1260 | 585-380 | 2500 |

| | | naya | | | |

* 1 am \u003d 1 kgf / cm2 @ 0.1 Mn / m2.

The basis of the crystal structure of crystalline material is a three-dimensional framework,

built of tetrahedrons connecting through common oxygen (5104).

However, the symmetry of their arrangement, packing density and mutual

orientations are different, which is reflected in the symmetry of crystals of individual

minerals and their physical properties... The exception is stishovite,

the basis of the structure of which are octahedra (SiO6), which form the structure,

similar to rutile. All quartz crystals (except for some varieties of quartz)

usually colorless. The hardness on the mineralogical scale is different: from 5.5 (a-

tridymite) to 8-8.5 (stishovite).

K. m. Are usually found in the form of very small grains, cryptocrystalline

fibrous (a-cristobalite, so-called lussatite) and sometimes spheroidal

formations. Less often - in the form of crystals of tabular or lamellar

shape (tridymite), octahedral, dipyramidal (a- and b-cristobalite),

fine-needle (coesite, stishovite). Most quartz m. (Except for quartz) are very

rare and unstable in the surface zones of the earth's crust.

High-temperature modifications SiO2 - 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 constituent parts of agates, chalcedony, opals; deposited

from hot aqueous solutions, sometimes from colloidal SiO2. Stishovite and Coesite

found in the sandstones of the Devil's Canyon meteoric crater in Arizona (USA),

where they were formed due to quartz at instantaneous ultrahigh pressure and

when the temperature rises during a meteorite fall. In nature also

occur: quartz glass (so-called leschatelite), formed in

as a result of the melting of quartz sand from a lightning strike, and melanoflogite - in

in the form of small cubic crystals and crusts (pseudomorphs consisting of

opal-like and chalcedony-like quartz), grown on native sulfur in

deposits of Sicily (Italy). Kitite has not been found in nature.

Quartz (German Quarz), mineral; under the name K., two crystalline

modifications of silicon dioxide SiO2: hexagonal K. (or a-K.), stable

at a pressure of 1 atm (or 100 kn / m2) in the temperature range 870-573 ° C, and

trigonal (b-K.), stable at temperatures below 573 ° C. b-K. most

is widely found in nature. It crystallizes in the trigonal class

trapezohedron of the trigonal system. Frame-type crystal structure

built of silicon-oxygen tetrahedra arranged in a helical (with

right or left screw stroke) with respect to the main axis of the crystal. IN

depending on this, right and left structural and morphological

crystal shapes that differ externally in the symmetry of the arrangement of some

faces (for example, trapezohedron, etc.). Lack of planes and center

symmetry in crystals K. determines the presence of piezoelectric and

pyroelectric properties.

Most often crystals of K. have an elongated-prismatic appearance with

the predominant development of the faces of a hexagonal prism and two rhombohedrons

(crystal head). Less often, crystals take the form of a pseudo-hexagonal

bipyramids. Externally regular crystals of K. are usually complexly twinned,

forming the most often twinned areas on 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 at thermal a - b

transitions accompanied by compression, as well as mechanical deformations.

The color of crystals, grains, and aggregates is very diverse: the most common

colorless, milky white or gray K. Transparent or translucent

beautifully colored crystals, especially called: colorless, transparent -

rhinestone; purple - amethyst; smoky - rauchtopaz; black

Morion; golden yellow - citrine. Different colors are usually due to

structural defects when replacing Si4 + with Fe3 + or Al3 + with simultaneous

entering into the lattice Na1 +, Li1 + or (OH) 1-. Also difficult to meet

colored stones due to microinclusions of foreign minerals: green prase

Inclusions of microcrystals of actinolite or chlorite; golden shimmer

aventurine - inclusions of mica or hematite, etc. Cryptocrystalline

varieties K. - agate and chalcedony - consist of the finest fibrous

formations. To. Optically uniaxial, positive. Refractive indices

(for daylight l \u003d 589.3): ne \u003d 1.553; no \u003d \u003d 1.544. Transparent for

ultraviolet and partly infrared rays. When transmitting light

a plane-polarized beam in the direction of the optical axis, left-handed crystals K.

rotate the plane of polarization to the left, and the right - to the right. In the visible part

spectrum, the value of the angle of rotation (per 1 mm thickness of the K.

32.7 (for l 486 nm) to 13.9 ° (728 nm). Dielectric value

permeability (eij), piezoelectric modulus (djj) and elastic

the coefficients (Sij) are as follows (at room temperature): e11 \u003d 4.58; e33 \u003d

4.70; d11 \u003d -6.76 * 10-8; d14 \u003d 2.56 * 10-8; S11 \u003d 1.279; S12 \u003d - 0.159; S13 \u003d

0.110; S14 \u003d -0.446; S33 \u003d 0.956; S44 \u003d 1.978. Linear coefficients

expansions are: perpendicular to the axis of the 3rd order 13.4 * 10-6 and

parallel to the axis 8 * 10-6. The heat of transformation b - a K. is 2.5 kcal / mol

(10.45 kJ / mol). Mineralogical hardness 7; density 2650

kg / m3. It melts at a temperature of 1710 ° C and solidifies when cooled in the so-called.

quartz glass. Fused K. is a good insulator; cube resistance with

an edge of 1 cm at 18 ° С is 5 * 1018 ohm / cm, the coefficient of linear expansion

0.57 * 10-6 cm / ° C. An economically viable cultivation technology has been developed

synthetic monocrystals, which are obtained from aqueous solutions of SiO2

at elevated pressures and temperatures (hydrothermal synthesis). Crystals

synthetic K. have stable piezoelectric properties,

radiation resistance, high optical uniformity and other valuable

technical properties.

Natural K. is a very widespread mineral that is essential

an integral part of many rocks, as well as deposits of useful

fossils of the most diverse genesis. Most important for

industry quartz materials - quartz sands, quartzites and

crystalline monocrystalline K. The latter is rare and very

highly regarded. In the USSR, the main crystal deposits of K. are in the Urals, in

Ukrainian SSR (Volyn), 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

ceramic and glass industry. Monocrystals K. find

application 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 K. is used for

making special chemical glassware. K. is also used for

obtaining chemically pure silicon. Transparent, beautifully colored

varieties of K. are semi-precious stones and are widely used in

jewelry business.

Quartz glass, one-component silicate glass obtained by melting

natural varieties of silica - rock crystal, vein quartz and

quartz sand, as well as synthetic silicon dioxide. Distinguish between two

type of industrial K.s .: transparent (optical and technical) and

opaque. Opacity To. Page. Gives a large amount

small gas bubbles distributed in it (with a diameter of 0.03 to 0.3

μm), scattering light. Optical transparent K.s. obtained by melting

rock crystal, completely homogeneous, does not contain visible gas

bubbles; has the lowest indicator among silicate glasses

refraction (nD \u003d 1.4584) and the highest light transmittance, especially for

ultraviolet rays. For K. with. characterized by high thermal and

chemical resistance; softening temperature K. page. 1400 ° C. K. s. good

dielectric, specific electrical conductivity at 20 ° С-10-14 - 10-16 ohm-

1m-1, dielectric loss tangent at 20 ° C and frequency

106 Hz - 0.0025-0.0006. K. s. used for the manufacture of laboratory

dishes, crucibles, optical instruments, insulators (especially for high

temperatures), products resistant to temperature fluctuations.

Silanes (from Lat. Silicium - silicon), silicon compounds with total hydrogen

formulas SinH2n + 2. Silanes up to octasilane Si8H18 were obtained. When

room temperature, the first two K. - monosilane SiH4 and disilane Si2H6 -

gaseous, the rest are volatile liquids. All K. have an unpleasant odor,

poisonous. K. is much less stable than alkanes in air

self-igniting, for example 2Si2H6 + 7O2 \u003d 4SiO2 + 6H2O. Water decomposes:

Si3H8 + 6H2O \u003d 3SiO2 + 10H2. In nature, K. are not found. In the laboratory by action

diluted acids into magnesium silicide, a mixture of various K. is obtained, its

strongly cooled and separated (by fractional distillation in the complete absence of

air).

Silicic acid

Silicic acids, derivatives of silicic anhydride SiO2; very weak

acids, slightly soluble in water. In its pure form,

metasilicic acid H2SiO3 (more precisely, its polymeric form H8Si4O12) and

H2Si2O5. Amorphous silicon dioxide (amorphous silica) in aqueous solution

(solubility about 100 mg in 1 l) forms predominantly orthosilicon

acid H4SiO4. In supersaturated solutions of K. to. Obtained in different ways.

change with the formation of colloidal particles (molar mass up to 1500), by

whose surfaces are OH groups. Educated so on. sol in

depending on the pH, the pH can be stable (pH about 2)

or it can aggregate to form a gel (pH 5-6). Sustainable

highly concentrated sols of K. to., containing special substances -

stabilizers, used in the manufacture of paper, in textile

industry, for water purification. Fluorosilicic acid, H2SiF6,

strong inorganic acid. It exists only in aqueous solution; in

free form decomposes into silicon tetrafluoride SiF4 and hydrogen fluoride

HF. It is used as a strong disinfectant, but mainly -

to obtain salts of K. to. - silicofluorides.

Silicates

SILICATES, silicon acid salts. Most widespread in the earth's crust

(80% by weight); more than 500 minerals are known, among them are precious

stones such as emerald, beryl, aquamarine. Silicates are the basis of cements,

ceramics, enamels, silicate glass; raw materials in the production of many metals,

adhesives, paints, etc .; radio electronics materials, etc. Silicon fluorides,

fluorosilicates, salts of hydrofluorosilicic acid H2SiF6. When heated

decompose, for example CaSiF6 \u003d CaF2 + SiF4. Salts Na, K, Rb, Cs and Ba hard

soluble in water and form characteristic crystals, which is used in

quantitative and microchemical analysis. Most practical

has sodium silicofluoride Na2SiF6 (in particular, in the production

acid-resistant cements, enamels, etc.). A significant proportion of Na2SiF6

processed to NaF. Obtain Na2SiF6 from waste containing SiF4

superphosphate plants. Silicon fluorides Mg, Zn and Al readily soluble in water

(technical name fluates) are used for waterproofing

building stone. All K. (as well as H2SiF6) are poisonous.

Applications.

Fig. 1 Right and left quartz.

Fig. 2 Silica minerals.

Fig. 3 Quartz (structure)