Composition of silicon chemistry. Optimization of a new method of obtaining clean silicon
To isolate clean silicon, chemists conduct a quartz sand with magnesium. Also, silicon is paid at high temperatures and even "grown". The Czokralsky method allows the use of pressure, temperature and silicon compound to obtain crystals of pure substance.
Life
Silicon compounds are actively used in the household and human farm, in industry. Quartz sand is used in obtaining glass and cement. Silicate industry is named so in honor of silicon, the "second name" of which "Silicium". Silicates are used in agriculture, When fertilizing the soil. Also, silicate glue is also obtained based on silicon compounds.Radioelectronics
Silicon has unique radio electronic properties. Clean silicon is a semiconductor. This means that it can carry out current under certain conditions when the conduction zone is small. If the conduction area is large, the silicon semiconductor turns into a silicon insulator.Semiconductor properties of non-metallol silicon led to the creation of a transistor. The transistor is a device that allows you to control the voltage and current strength. Unlike linear conductors, silicon transistors have three main elements - a collector, "collecting" current, database and emitter, reinforcing current. The appearance of the transistor caused an "electronic boom", led to the creation of the first computers and household appliances.
Computers
Silicon's successes in electronics did not remain unnoticed in computer technician. At first, processors wanted to do from the "expensive" typical semiconductors, for example, Germany. However, its high price did not allow to put the production of Germany boards on the flow. Then the bolts from IBM decided to risk and try as a material for the "heart" of the computer system of silicon. The results did not make it wait.Silicon boards turned out to be quite cheap, which was especially important at the very beginning of the generation of the computer industry, when there was a lot of marriage and few potential buyers.
Today, silicon microcircuits dominate the computer industry. Clean silicon crystals for processors and controllers have learned to grow in factory conditions, the material is easy to operate. And the main thing - silicon allowed to double the number of elements on the processor every two years (the Moore law). Thus, on the silicon scheme of the same size, more and more transistors and other logical elements are becoming more and more. Silicon allowed to do information Technology Maximum efficient as possible.
Course work on the topic:
Optimization of the new method of receipt
clean silicon.
Prepared: coastal Daniel
Subbotin Dmitry.
Leader:
moscow. Sunz Moscow State University
2012
Introduction
The theme of obtaining polycrystalline silicon by aluminothermia is relevant to the fact that it provides for the consideration of a new method for producing polycrystalline silicon without the extensive costs of material and time resources. The product produced by this method can be a cheap raw material for further processing.
This work is new in that it uses the easiest, previously unused method for obtaining clean silicon.
In the future, within the framework of operation, the required product will be obtained - polycrystalline silicon, the method of recovery of silicon dioxide by aluminum.
Tasks of work:
1. Analysis of modern methods for obtaining silicon;
2. Optimization of the new method of obtaining the final product.
Silicon as an element.
Silicon in nature.
According to the prevalence in the earth's crust of silicon, among all elements, it takes second place (after oxygen). Silicon accounts for 27.7% of the mass of the earth's crust. Silicon is part of several hundred different natural silicates. Among them, Al4 (OH) 8 kaolinite, topaz Al2 (SiO4) Fe2, aluminosilicates (field spasps, mica, clay minerals, etc.). Widespread and silica, or silicon oxide (IV) - SiO2 (river sand, quartz, flint, etc.), which makes up about 12% of the earth's crust (by mass). In the free form of silicon in nature is not found. SiO2 silicon is also included in the composition of plant and animal organisms.
Chemical and physical properties of silicon.
Silicon (silicium) Si, chemical element IV group periodic system, Atomic number 14, atomic weight 28.0855. It consists of three stable isotopes (92.27%), (4.68%) and (3.05%). Configuration of the outer electron shell of the silicon atom -; The degree of silicon oxidation is +4 as the most stable, as well as +3, +2 and +1. Atomic radius -0,133, ion radius - 0.040 nm with a coordination number 4, and 0.054 nm with a coordination number 6), a covalent radius is 0.1175 nm.
Compact silicon is a silvery-gray substance with a metal glitter. Crystal lattice of stable modification of cubic grazent-center, type of diamond. (See Appendix.) At high pressures, there are other polymorphic modifications: at 20 GPa - silicon I with a tetragonal lattice, above 20 GPa - silicon II with cubic grille and silicon III with a hexagonal grid. Under normal conditions, silicon fragile, and at temperatures above 800 ° C becomes plastic. Electrophysical properties of silicon depend on the nature and concentration of impurities present and structural defects. To obtain silicon monocrystals with hole conductivity, use alloying additives B, Al, Ga, In, with electronic conductivity - P, AS, SB. The impurities of AU, CU, Fe, Mn, V and some others significantly reduce the lifetime of current carriers in silicon monocrystals. The maximum solubility of the impurities in silicon is observed at a temperature of in ° C. The electrical properties of silicon can be strongly changed during thermal processing. Thus, the heating of single crystals containing oxygen, up to 400-500 ° C leads to an increase in electron conductivity, and with sequential heating to ° C, this effect disappears. Usually, heat treatment leads to a significant reduction in current speaker life.
At low temperatures, silicon is chemically inert, but when heated, its reactivity increases sharply. Especially active melted silicon. The coordination number of silicon atom 4, sometimes 6, for example, in fluorosilicates containing anion. Compounds where silicon is formally bivalent, apparently contains the Si-Si connection and, as a rule, polymer. Due to the silicon resistant oxide film forming on the surface, even at elevated temperatures. Amorphous silicon has the ability to dissolve significant amounts of different gases, primarily H2. In this case, a solid solution is formed with a hydrogen content of up to 47%, called L-Si: H, which has semiconductor properties. With nitrogen higher at a temperature of 1000 ° C, silicon forms Si3N4 nitride silicon, with phosphorus - SIP phosphide, with arsenic - SIAS2 and SIAS arsenides, with carbon - silicon SIC carbide, with boron - thermally and chemically resistant Borides SIB3, SIB6 and SIB12. Most metals give refractory high-sided silicides.
Biological properties of silicon.
For some organisms, silicon is an important biogenic element. It is part of the supporting formations in plants and skeletal - in animals. In large quantities of silicon, marine organisms are concentrated - diatoms of algae, radolaria, sponges. Muscular fabric fabric contains (1-2) ·% silicon, bone tissue - 17 ·%, blood - 3.9 mg / l. With food in the human body daily comes up to 1 g of silicon.
Silicon compounds are not poisonous, but inhalation of highly dispersed particles, both silicates and silica dioxide formed, for example, with explosive works, when driving breeds in mines, during the operation of sandblasting devices is extremely dangerous. SiO2 microparticles that have fallen into the lungs are crystallized in them, and the cristalline arms destroy the pulmonary tissue and cause severe disease - silicos.
Get full textHistory of application
Natural compounds of silicon - silicon dioxide (silica) - are known for a very long time. Ancient well knew rhinestone, or quartz, as well as precious stones, which are painted in different colors quartz (amethyst, smoky quartz, chalcedony, chrysoprase, topaz, onyx, etc.) from silicon in prehistoric times did the first stone guns - tips for arrows and copies, scrapers, fire. For the 5th centuries, flints were used for arson of gunpowder in guns and guns, since, when he was blowing the chairs about the flint, a long-lived spark was burned. There is evidence that the warriors of Alexander Macedonsky, leaving the campaign, had to have a bag filled with silicon with them, and Peter I insisted, and Peter I. Both commander knew about the properties of silicon to purify water. In Russia, silicon was made to lay out the bottom of the wells in order to clean the water. The use of silicon compounds associated with their processing is the manufacture of glass - began in yet Ancient Egypt About 3000 years BC e.
The name of Silicia or Kizel (Kiesel, Flint) was suggested by Berzelius. Even, Thomson offered the name Silicon (Silicon), adopted in England and the United States, by analogy with the Boron (Borbon) and Carbon (Carbon). The word of Silicium (Silicium) comes from silica (silica); The end of "A" was taken in the XVIII and XIX centuries. For lands designation (Silica, Aluminia, Thoria, Terbia, Glucina, Cadmia, etc.). In turn, the word of Silica is connected with the lat. Silex (strong, flint).
Russian Name of silicon comes from the Vine Slavic Words, Kremitics, Strong, Condet, Cessica (hit iron about the belt for obtaining sparks) and others. In Russian chemical literature early XIX. in. There are "silica" names (Zakharov, 1810), "Silia" (Solovyov, Dvigubsky, 1824), "Flint" (fears, 1825), "silica" (Iovsky, 1827), "silica" and "silicon" (hess, 1831).
Elementary silicon was obtained only in the XIX century, although the attempts to decompose silica were taken by the shehele and Lavoisier, Davy (using the Voltov Post), Gay Loussak and Trenar (chemical path). Britzelius, seeking to decompose silica, heated it in a mixture with an iron powder and coal to 1500 ° C and received ferrosilica. Only in 1823, during the studies of the compounds of plaguing acid, including SiF4, it received free amorphous silicon ("radical silica") interaction of fluoride of silicon and potassium vapor. Saint Clare Deville in 1855 received crystalline silicon.
The use of silicon in the modern industry.
To date, silicon has been widespread in many areas of industry.
Technical silicon finds applications as raw materials for metallurgical industries. It is used as a component of alloys (bronze, silumin); deoxidizer when smelting cast iron; The properties of metals or the alloying element, for example, the addition of a certain amount of silicon in the production of transformer steels increases the coercive force (a demagnetizing external magnetic field) of the finished product.
Also, technical silicon is used as raw materials for the production of cleaner polycrystalline silicon and purified metallurgical silicon.
Silicon - Raw materials for the production of silicone materials (compounds, in the molecules of which there is a link between silicon and carbon atoms) and silanes.
Sometimes silicon of technical purity and its alloy with iron - ferrosilication, is used to produce hydrogen in the field. Silicon dissolves in a hot alkali solution with hydrogen release: Si + 4Naoh \u003d Na4SiO4 + 2H2.
Ultrapure silicon is used to produce single electronic devices (nonlinear passive elements of electrical circuits) and one-chip chip.
Clean silicon, supercine silicon waste, purified metallurgical silicon in the form of polycrystals are the main raw material for solar energy.
Monocrystalline silicon - in addition to electronics and solar energy used for the manufacture of gas lasers mirrors.
Compounds of silicon metals - silicides are widely consistent in industry (for example, electronic and atomic) materials with a wide range of useful chemical, electrical and nuclear properties (resistance to oxidation, neutron, etc.). Silicides of a number of elements are important thermoelectric materials.
Silicon compounds serve as the basis for the production of glass and cement. Silicate industry is engaged in the production of glass and cement. She also produces silicate ceramics - brick, porcelain, faience and products of them.
Silicate glue, used in construction as a sequivalent, and in pyrotechnics and in everyday life for gluing paper.
Silicone oils and silicones are also obtained - materials based on silicone compounds.
Growing crystals
Most of the methods for obtaining clean silicon are associated with obtaining poly - or single crystals.
Causes and conditions for the formation of crystals
Get full textMaterial particles (atoms, molecules, ions), gorges or liquid (molten) substances, having high kinetic energy, are in continuous motion. From time to time they face, forming germs - microscopic fragments of the future structure. Most often, such embryos disintegrate, which is connected either with their own oscillations, or with bombing by their free particles. However, to start crystallization, it is necessary that the germ reaches a critical value, i.e. contained such a number of particles, in which the addition of the next particle would make the growing of the embryo energetically more profitable than its decay. Such an opportunity for most substances is manifested either with a decrease in temperature, as a result of which the temperature fluctuations are reduced, or with an increase in the concentration of the substance in solution or gas, which leads to an increase in the likelihood of a part of the particles with each other, that is, to the emergence of the embryos.
Thus, crystal growth can be considered as a process by which the smallest crystalline particles are embryos - reach macroscopic sizes. Moreover, crystallization proceeds not in all volumes, but only where the embryos arise. Factors affecting the appearance of embryos are not only a hypothermia and an increase in the concentration of the solution or viscosity of the melt, but also the presence of foreign crumples of crystals or dust, on the surface of which particles are collected, simplifying the beginning of crystallization.
The crystallization process is energetically advantageous. The growing crystal does not make an equilibrium form due to the fact that various changing crystallization conditions affect it: temperature, pressure, gravity, chemical composition and medium dynamics, etc.
Growth mechanisms of crystals
At the end of the XIX century. American physicist J. Gibbs (), French physicist P. Curie and a Russian crystallograph on a thermodynamic basis, a quantitative theory of origin and growth of crystals was developed. Somewhat later, in the 20s. XX century, German physicist M. Volmer () the theory of spontaneous nucleation of crystals and their growth was put forward.
Following the thermodynamic teaching of Gibbs in 1927, the theoretical works of the German Physico-Chemist V. Kossel (1888 - 1956) and Bulgarian physics (1, which posted the beginning of the molecular-kinetic theory of crystal growth were obtained. They considered the growth of the perfect crystal (deprived of defects, inevitable In real crystals) with insignificant oversaturation without taking into account the imperfections of real crystals and the effects of crystallization medium. This theory explained the phenomenon of layer-layer crystal growth from the standpoint of the atomic molecular state of the growing crystal surface, based on the energy beneficiality of the addition of individual particles of the substance in various positions on the surfaces free from surface defects crystals.
In the process of growth, either atomic smooth, or atomic rough edges arise. Atomic-smooth faces are growing by layer-by-layer sediment of the substance and remain in the process of growth macroscopically flat. Such growth is called tangential or layers. At the same time, the growth rate of various faces will be different. As a result, the crystals will grow in the form of a polyhedron.
Crystals with atomic rough edges can attach particles from a macroscopic point of view to almost any point of the surface. Such growth is called normal. At the same time, the growth rates of the edges of the crystal in different directions will be about the same and crystals will acquire rounded forms. Growth in atomic rough planes and ends of steps requires only potential barriers to embedding individual atoms or molecules. The growth of atomic smooth surfaces requires the formation of steps, i.e., for the growth of each new layer, it is necessary to appear on the surface of a new embryo, and this is not always possible due to a lack of suction. In this case, the growth occurs only by moving existing steps. Thus, the first process from an energy point of view is more profitable.
In addition, the verge of real crystals is almost never ideal. There are always violations on their surfaces - defects, thanks to which screw and edge dislocations arise. The rise of the faces occurs on the helix by unsaluing one layer to another. And such an increase can occur with how many small sleeves and even from vapors. Dislocations, therefore, are a continuously active source of layers and remove the need to appear on the surface of the growing face of two-dimensional embryos.
Crystal growth shapes
Monocrystals are completely different forms and sizes (see annex), but at various deviations from the ideal crystallization conditions (for example, exotic formations grow in viscous, contaminated or severely persons). Experience shows that with small suggestions and supercooling on the growth plant there are perfect - grades - forms of crystals. With an increase in the deviation from the equilibrium, the crystals change their appearance, turning into skeletons, dendrites (from Greek. Dendron - tree), threaded formations or spherical crystals. These forms differ in the fact that skeletal crystals are single crystals, and dendrites are most often polycrystalline formations.
Get full textDefects of crystals(see Attachment)
Crystal defects are called any violation of the ideal periodicity of the crystalline lattice and distinguish several varieties of defects in dimension: zero-dimensional (point), one-dimensional (linear), two-dimensional (flat) and three-dimensional (volume) defects.
All defects that are associated with the displacement or replacement of a small group of atoms (own point defects) are applied to zerimer crystal defects. They occur when heated, doping, in the process of crystal growth and as a result of radiation irradiation.
Dotted defects include:
An analysis by the method of raster electron microscopy was performed on the device LEO SUPRA 50 VP (Germany). An increase in the shooting of micrographs was from × 500 to × 100 000.
Micrographs turned out fuzzy, since for this method of microscopy, the sample must be a conductor, and silicon is a semiconductor. But, despite this, the crystalline bodies can be considered in photographs with a small magnification.
Analysis of the peaks of the X-ray diagram showed that the product is present a large number of impurities of difficulty and extremely inert compounds of aluminum and silicon oxides. Based on these data, it can be concluded that the technique is imperfect and needs further refinement.
Literature:
1., filamentous crystals, M., 1969;
2. Modern composite materials, ed. L. Butman and R. Kroka, lane. from English, M., 1970;
3. Monocrystall fibers and materials reinforced by them, feathers. from English, M., 1973; Kelly A.,
4. High-strength materials, per. from English, M., 1976; .
5. Growth of filamentary and lamellar crystals from steam, M., 1977;
6. Fillers for modern composite materials, per. from English, M., 1981; .
7. Future materials. On the filamentous crystals of metals. M., 1989.
8., Aluminumermic production of ferroalloys and ligatures, M., 1963.
9. Magazine "Chemistry and Life" 1982, 3 release, p. 63.
10. Bulach with crystallography bases. M.: Alfa-M, 1989. - 156 p.
11. Egorov-Tismenko and Crystalochemistry: Textbook. - M.: KDU, 2005. - 592 p.
12., Shafranovsky. M.: Gosgeo - LTehizdat, 1955 - 215s.
Silicon is one of the most common elements in the earth's crust. It is (mass.) A part of the earth's crust available to our study, taking the second place after oxygen. In nature, silicon is found only in silicon dioxide (dioxide), also called silicon anhydride or silicate, and in the form of silicon acid salts (silicates), the most widespread in nature aluminosilicates, i.e. silicates, which are included, aluminum These include field swipes, mica, kaolin, etc.
As carbon, entering all organic substances, is an essential element of the plant and animal kingdom, so silicon is the main element in the kingdom of minerals and rocks.
In most organisms, silicon content is very small. However, some marine organisms accumulate large quantities of silicon. To their rich marine plants include diatoms of algae, many silicon animals contain radiolearies, silicon sponges.
Free silicon can be obtained by calcining with magnesium fine white sand, which is silicon dioxide:
At the same time, brown powder of amorphous silicon is formed.
Silicon soluble in molten metals. With slow cooling of the silicon solution in the zinc or in aluminum, silicon is released in the form of well-formed crystals of octahedral form. Crystal silicon has steel glitter.
High purity silicon crystals having a minimum number of structure defects are characterized by very low electrical conductivity. Impurities and violations of the structure of the structure sharply increase their conductivity.
Silicon is mainly used in metallurgy and in semiconductor technique. In metallurgy, it is used to remove oxygen from molten metals and serves as an integral part of many alloys. The most important of them are alloys based on iron, copper and aluminum. In semiconductor technology, silicon is used for the manufacture of photocells, amplifiers, rectifiers. Silicon-based semiconductor devices withstand heating before, which expands their scope.
In industry, silicon is obtained by the restoration of silicon dioxide with coke in electrical furnaces:
The silicon obtained according to this method contains impurities. Required for the manufacture of high purity silicon semiconductor devices are obtained more difficult. Natural silica is translated into such a compound of silicon, which is amenable to deep cleaning. Silicon is then isolated from the resulting pure matter by thermal decomposition or reducing agent. One of these methods is to convert silica in silicon chloride, cleaning this product and restoring silicon from it with high-purity zinc, very pure silicon can also be obtained by thermal decomposition of silicon or silane.
The resulting silicon contains very little impurities and is suitable for the manufacture of some semiconductor devices. To obtain an even cleaner product, it is subjected to additional cleaning, such as zone smelting (see § 193).
In chemical relations silicon, especially crystalline, is low-effective; At room temperature, it is directly connected only with fluorine. When heating, amorphous silicon is easily connected to oxygen, halogens and gray.
Acids, in addition to the mixture of fluoride hydrogen and nitric acid, do not act on silicon, but alkali react vigorously with it, highlighting hydrogen and forming salts of silicic acid:
In the presence of alkali traces, which plays the role of a catalyst, silicon displaces hydrogen from water.
If the mixture of sand and coke, taken in a certain ratio, is obtained in an electric furnace, then a silicon compound is obtained with carbon carbide, called carborund:
Pure carburund - colorless very solid crystals (density 3.2). The technical product is usually painted with impurities in a dark gray color.
According to the inner structure, carbarund is a diamond in which half of the carbon atoms is evenly replaced by silicon atoms. Each carbon atom is located in the center of the tetrahedron, in the vertices of which are silicon atoms; In turn, each silicon atom is surrounded by four carbon atoms in a similar way. Covalent bonds connecting all atoms in this structure, as in diamond, are very durable. This explains the big hardness of Carborund.
Carborund is obtained in large quantities; Its use is varied and is associated with its high hardness and refractory. Carbard powder manufactures grinding wheels, bars, grinding paper. On it, it produces plates for the construction of floors, platforms and transitions in the subway and at the station. The muffles and lining for various furnaces are prepared from it. A mixture of carbard and silicon powders serves as a material for the manufacture of silita rods for electric furnaces.
At high temperature, silicon comes into connection with many metals, forming silicides. For example, when silicon dioxide is heated with an excess of metallic magnesium, reconstructing silicon is combined with magnesium, forming magnesium silicide.
Chemical Silicon Sign Si, Atomic Weight 28,086, Kernel Charge +14. As, is located in the main subgroup of the IV group, in the third period. This is an analogue of carbon. Electronic configuration of electronic layers of silicon atom LS 2 2S 2 2P 6 3S 2 3P 2. The structure of the external electronic layer
The structure of the outer electron layer is similar to the structure of the carbon atom.
It is found in the form of two allotropic modifications - amorphous and crystalline.
Amorphous - brown-colored powder, which has several greater chemical activity than crystalline. At normal temperature reacts with fluorine:
Si + 2F2 \u003d SiF4 at 400 ° - with oxygen
Si + O2 \u003d SiO2
In melts - with metals:
2mg + Si \u003d Mg2Si
Crystalline silicon is a solid fragile substance with a metal glitter. It has good heat and electrical conductivity, easily dissolved in molten metals, forming. Silicon alloy with aluminum is called a silicon, silicon alloy with iron-ferrosilicia. Silicon density 2.4. Melting point 1415 °, Boiling point 2360 °. Crystalline silicon - the substance is rather inert and in chemical reactions with difficulty. With acids, despite well-noticeable metallic properties, silicon does not react, and alkalis reacts, forming salts of silicic acid and:
Si + 2Kon + H2O \u003d K2SIO2 + 2H2
■ 36. What is the similarity and what is the difference between the electronic structures of silicon and carbon atoms?
37. How to explain from the point of view of the electron structure of a silicon atom, why metallic properties are more characteristic of silicon than for carbon?
38. List the chemical properties of silicon.
§ 85. Silicon in nature. Silica
In nature, silicon is widespread very wide. Approximately 25% of the earth's crust falls on silicon. A significant part of natural silicon is represented by SiO2 silicon dioxide. In a very pure crystalline state, silicon dioxide is found in the form of a mineral called a mountain crystal. Silicon dioxide and carbon dioxide chemical composition are analogues, however, carbon dioxide is gas, and silicon dioxide - solid. In contrast to the molecular crystal grille CO2, SiO2 silicon dioxide crystallizes in the form of an atomic crystal lattice, each cell of which is a tetrahedron with a silicon atom in the center and oxygen atoms in the corners. This is explained by the fact that the silicon atom has a larger radius than carbon atom, and not 2, and 4 oxygen atoms can be accommodated around it. The difference in the properties of these substances is explained in the structure of the crystal lattice. In fig. 69 are shown appearance A natural quartz crystal consisting of pure silicon dioxide, and its structural formula.
Crystal silicon dioxide is most often found in the form of sand, which has white colorUnless contaminated with clay impurities of yellow. In addition to sand, silicon dioxide is often found in the form of a very solid mineral - silicon (hydrated silicon dioxide). Crystalline silicon dioxide, painted in various impurities, forms precious and semi-precious stones - agate, amethyst, yashma. Almost pure silicon dioxide is also found in the form of quartz and quartzite. Free silicon dioxide in the earth's crust is 12%, as part of various rocks - about 43%. A total of more than 50% of the earth's crust consists of silicon dioxide.
Silicon is part of a variety of rocks and minerals - clay, granites, shenitites, mica, field swaps, etc.
The solid carbon dioxide, without melting, is removed at -78.5 °. The melting point of silicon dioxide is about 1.713 °. She is quite turning. Density 2.65. Silicon dioxide expansion coefficient is very small. It is very important when applying basin glassware. In water, silicon dioxide does not dissolve and does not react with it, despite that it is acidic oxide and it corresponds to H2SiO3 silicon acid. Carbon dioxide in water, as well as soluble. With acids, except for hydrofluoric acid HF, silicon dioxide does not react, with alkalis gives salts.
Fig. 60. Structural formula of silicon dioxide (a) and natural quartz crystals (b)
Fig. 69. Structural formula of silicon dioxide (a) and natural quartz crystals (b).
When powering silicon dioxide with coal, silicon is recovered, and then its compound with carbon and the formation of carbarund in the equation:
SiO2 + 2c \u003d SiC + CO2. Carbarund has a high hardness, to acids stable, and alkalis is destroyed.
■ 39. What properties of silicon dioxide can be judged by its crystal lattice?
40. In the form of what minerals silicon dioxide is found in nature?
41. What is carborund?
§ 86. Silician acid. Silicates
H2SIO3 silicon acid is a very weak and small-resistant acid. When heated, it gradually decomposes into water and silicon dioxide:
H2SIO3 \u003d H2O + SiO2
In water, silicic acid is practically insoluble, but can easily give.
Silicon acid forms salts called silicates. Widely found in nature. Natural is quite complicated. Their composition is usually depicted as a connection of several oxides. If aluminum oxide enters the natural silicates, they are called aluminosilicates. Such are white clay, (kaolin) Al2O3 · 2SiO2 · 2H2O, field swipe K2O · Al2O3 · 6SiO2, mica
K2O · Al2O3 · 6SiO2 · 2N2O. Many natural in pure form are precious stones, for example, Aquamarine, Emerald, etc.
Artificial silicates should be noted Silicate sodium Na2SiO3 - one of the few water soluble silicates. It is called soluble glass, and a solution - liquid glass.
Silicates are widely used in the technique. Soluble glass impregnate fabrics and wood to protect them from ignition. Liquid is part of refractory smear for gluing glass, porcelain, stone. Silicates are the basis in the production of glass, porcelain, faience, cement, concrete, bricks and various ceramic products. Silicate solutions are easily hydrolyzed in solution.
§ 87. Glass
The raw materials for the production of glass are the soda Na2CO3, the Limestone SASO3 and SiO2 sand. All components of the glass charge are thoroughly cleaned, mixed and fused at a temperature of about 1400 °. The following reactions take place in the fusion process:
Na2CO3 + SiO2 \u003d Na2SiO3 + CO2
Caco3 + SiO2 \u003d Casio 3+ CO2
In fact, the composition of the glass includes sodium silicates and calcium, as well as excess SO2, so the composition of the conventional window glass: Na2O · Cao · 6SiO2. The glass mixture is heated at a temperature of 1500 ° until carbon dioxide is completely removed. Then cooled to a temperature of 1200 ° at which it becomes viscous. As any amorphous substance, glass softened and hardens gradually, so it is a good plastic material. The viscous glass is passed through the gap, as a result of which a glass sheet is formed. The hot glass sheet is pulled by rolls, bringing to certain sizes and gradually cooling the air current. Then it is cut around the edges and cut onto a certain format sheets.
■ 44. Bring the equations of reactions leaking when the glass is obtained and the composition of the window glass.
Glass - The substance is amorphous, transparent, in water is practically insoluble, but if it is crushed into fine dust and mix with a small amount of water, in the resulting mixture with phenolphthalein, you can detect alkali. For long storage Alkali in glassware excess SiO2 in glass is very slowly reacting with alkali and glass gradually loses the transparency.
Glass became known to people for more than 3000 years before our era. In antiquity, glasses were obtained almost the same composition, as at present, but the ancient masters were guided only by their own intuition. In 1750 managed to develop scientific basis Glass production. For 4 years collected many recipes for the manufacture of different glasses, especially non-ferrous. At the glass factory built by him, a large number of glass samples were made, which were preserved to this day. Currently, glasses of different compositions with various properties are used.
Quartz glass consists of almost pure silicon dioxide and is solved from a mountain crystal. Its very important feature is that he has a slight expansion coefficient, almost 15 times less than that of ordinary glass. Cooking from such glass can be splitken with a burner flame and then omit in cold water; In this case, no changes with glass will happen. Quartz glass does not delay ultraviolet rays, and if you paint it with nickel salts in black, it will delay all the visible rays of the spectrum, but for ultraviolet rays will remain transparent.
Acids do not act on quartz glass and, but alkalis it is noticeably corrosive. Quartz glass is more fragile than the usual. Laboratory glass contains about 70% SiO2, 9% Na2O, 5% K2O 8% SAO, 5% AL2O3, 3% B2O3 (the composition of the glasses is not given to memorization).
In industry find the use of glass yen-skoe and pirex. The Ien glass contains about 65% Si02, 15% B2O3, 12% WAO, 4% ZnO, 4% Al2O3. It is firmly resistant to mechanical effects, has a small expansion coefficient, resistant to alkalis.
Pyrex glass contains 81% SiO2, 12% B2O3, 4% Na2O, 2% Al2O3, 0.5% AS2O3, 0.2% K2O, 0.3% SAO. It possesses the same properties as Ien glass, but even more, especially after quenching, but less sustainable alkalis. Pyrex glass manufactures household items that are undergoing heating, as well as parts of some industrial installations operating at low and high temperatures.
Different quality glass give some additives. For example, vanadium oxides impurities give glass, fully delaying ultraviolet rays.
Glass, painted in different colors also get. More made several thousand color glass samples of different color and shades for their mosaic paintings. Currently, glass color methods are designed in detail. Manganese compounds color glass in purple color, cobalt - in blue. , sprayed in the mass of glass in the form of colloidal particles, gives it a ruby \u200b\u200bcolor, etc. Lead compounds give glass glitter, similar to the brilliance of a rhinestone, so it is called crystal. Such glass is easily processing, cutting. Products from it very beautifully refract the light. When painting this glass, color crystal glass is obtained by various additives.
If the molten glass is mixed with substances that, with decomposition, form a large number of gases, the latter, released, foam glass, forming foam-glass. Such glass is very light, well processed, is an excellent electric and heat-insulator. It was first received by prof. I. I. Khorgorodsky.
Pulling the thread from glass, you can get the so-called fiberglass. If it is impregnated with fiberglass layers with synthetic resins, then it turns out very durable, not a declarationable, perfectly processed building material, the so-called fiberglass. Interestingly, the thinner fiberglass, the higher its strength. Fiberglass is also used for the manufacture of overalls.
Glass wool is a valuable material through which strong acids and alkalis can be filtered, not filtered through paper. In addition, glass wool is a good heat insulating substance.
■ 44. From what the properties of the glass depend different species?
§ 88. Ceramics
The aluminosilicates are especially important white clay - kaolin, which is the basis for obtaining porcelain and faience. Porcelain production is an extremely ancient branch of the economy. Motherland Porcelain - China. In Russia, porcelain was obtained for the first time in XVIII. D, I. Vinogradov.
Raw materials for the preparation of porcelain and faience, besides Kaolin, serve as sand and. A mixture of kaolin, sand and water is subjected to a thorough thin grinding in the ball mills, then filtered off the excess water and well-smeared plastic mass are directed to molding products. After the molding of the product, it is dried and burning in tunnel furnaces of continuous action, where they are first warmed up, then burn and finally cooled. After that, the product is further processed - the coating of icing, drawing with ceramic paints. After each stage, the product is burned. As a result, porcelain is obtained by white, smooth and brilliant. In thin layers, he shines. Faience Porridge and does not shine.
From red clay formulate bricks, tiles, clay dishes, ceramic rings for nozzles in absorbing and washing towers of various chemical production, flower pots. They are also burned so that they do not soften with water, steel is mechanically durable.
§ 89. Cement. Concrete
Silicon compounds serve as the basis for obtaining cement - binder material, indispensable in construction. Raw materials for receiving cement are clay and limestone. This mixture is burned in a huge inclined tubular rotating furnace, where raw materials are continuously loaded. After the firing at 1200-1300 ° from the hole located on the other end of the furnace, the appropriate mass is continuously coming out - clinker. After grinding clinker turns into. The cement includes mainly silicates. If mixed with water to the formation of thick casher, and then leave for some time in air, it will take a reaction with cement substances, forming crystallohydrates and other solid compounds, which leads to solidification ("setting") cement. This is no longer translated into the previous state, so before consuming cement is trying to take care of water. The process of cement hardening is long, and it acquires real strength only in a month. True, there are different grades of cement. The usual cement considered by us is called silicate, or portland cement. From alumina, limestone and silicon dioxide manufactures quickly hardening clamping cement.
If you mix cement with rubble or gravel, then a concrete is obtained, which is already an independent building material. Crushed stone and gravel are called fillers. Concrete has high strength and withstands heavy loads. It is water vehicles, fires. When heated almost does not lose strength, as it is very small thermal conductivity. Concrete of frostotes, weakens radioactive radiation, so it is used as a building material for hydrotechnical structures, for protective shells of nuclear reactors. Concrete is chosen boilers. If mixed cement with a foaming agent, it is formed a foam foam concrete cells. Such a concrete is a good soundproofer and even less than an ordinary concrete, carries out heat.
Properties 14 Si.
|
Atomic mass |
28,086 |
clark, at.% (Commonness in nature) |
16,7 |
|
Electronic configuration * |
State of aggregation (n. u.). |
solid |
|
|
0,132 |
Color |
dark Gray Brilliant |
|
|
0,034 |
1423 |
||
|
Ionization energy |
8,151 |
2355 |
|
|
Relative electrical negativity |
1,74 |
Density |
2,3263 |
|
Possible degrees of oxidation |
4, +2, +4 |
Standard electrode potential |
* The configuration of the external electronic levels of the element atom is given. The configuration of the remaining electronic levels coincides with that for the noble gas that the previous period and the above mentioned in brackets.
Finding in nature.Silicon after oxygen is the most common element in the earth's crust. Unlike carbon in the free state of silicon in nature is not found. The most common compounds are silicon oxide (IV) SiO 2 and silicon acid salts - silicates. They form the sheath of the earth's crust. Silicon compounds are contained in organisms of plants and animals.
Natural silicates have a complex composition and structure. Here is the composition of some natural silicates: field spar to 2 o × ал 2 O 3 × 6SIO 2, asbestos 3mGo × 2Sio 2 × 2H 2 O, Cutton to 2 × 3Al 2 O 3 × 6Sio 2 × 2H 2 O, Kaolinitis 3Al 2 O 3 × 2Sio 2 × 2H 2 O.
Silicates containing aluminum oxide in their composition are called aluminosilicates. From the above-mentioned silicates, aluminosilicates are field spat, kaolinitis and mica. In nature, aluminosilicates are most common, such as field spatts. Mixtures of various silicates are also common. So, rock rocks - granites and gneisses - consist of crystalline quartz, field spat and mica.
The main product of destruction is the mineral kaolinitis - the main component of the white clay. As a result of the weathelation of rocks, clay, sand and salts were formed.
Getting.In industry, silicon is obtained by the restoration of SiO 2 coke in electrical furnaces:
In the laboratory, magnesium or aluminum is used as reducing agents:
The most pure silicon is obtained by restoring silicon tetrachloride with zinc pairs:
Application. Silicon is used as a semiconductor. It is manufactured from it, so-called solar panels that convert light energy into electrical (power supply of spacecraft radoins). Silicon is used in metallurgy to obtain siliceous steels with high heat resistance and acid-absorption.
Physical properties. Crystalline silicon is a dark gray substance with steel glitter. The structure of silicon is similar to the structure of the diamond. In its crystal, each atom is surrounded by tetrahedralically four others and is associated with a covalent bond, which is much weaker than between carbon atoms in diamond. In silicon crystal, even under normal conditions, some of the covalent bonds are destroyed. Therefore, it has free electrons that determine a small electrical conductivity. When illuminating and heating, the number of destroyable bonds increases, which means that the number of free electrons is increasing and electrical conductivity increases. This should explain the semiconductor properties of silicon.
Silicon is very fragile, its density is 2.33 g / cm 3. Like coal, refers to refractory substances.
Silicon consists of three stable isotopes: 28 14 Si (92.27%), 29 14 Si (4.68%) and 30 14 S.i (3.05%).
Chemical properties.According to the chemical properties of silicon, like carbon, is non-metal, but its non-metallium is less pronounced, as it has a larger atomic radius. Since silicon atoms at the external energy level are 4 electrons, then the silicon is characterized by the degree of oxidation as -4 and +4 (a compound of silicon is known, where its oxidation degree is +2).
Silicon under normal conditions is quite inert, which should be explained by the strength of its crystal lattice. He directly interacts with fluorine only:
Acids (except for a mixture of Plavik HF and nitrogen HNO 3) do not act on silicon. However, it dissolves in alkali metal hydroxides, forming silicate and hydrogen:
Of the two allotropic modifications of silicon - crystalline and amorphous - chemically more active is amorphous silicon. It reacts with oxygen when heated, forming SiO 2:
as well as with all halogens, for example:
At high temperature, silicon is combined with carbon, forming carborundum SiC:
Carborund has a diamond-like crystal lattice, in which each silicon atom is surrounded by four carbon atoms and on the contrary, and covalent bonds are very durable, as in diamond. Therefore, by hardness, he is close to diamond. Silicon carbide produce grinding stones and grinding circles.
Magnesium silicide.In reactions with active metals leaking to form silicides Silicon acts as an oxidizing agent:
At high temperatures, silicon restores many metals from their oxides.
Sylan.Under action on hydrochloric acid silicides, the simplest hydrogen connection Silicon sylan Sih 4:
Sylan - Poisonous gas with an unpleasant smell, self-proposal in the air:
Silicon oxide (IV).Silicon oxide (IV) is also called silica. This is a solid refractory substance (melting point of 1700 ° C), widely distributed in nature in two types: 1) crystalline silica - in the form of a quartz mineral and its varieties (mountain crystal, chalcedony, agate, jasper, flint); Quartz is the basis of quartz sands, widely used in construction and in the silicate industry; 2) amorphous silica - In the form of the mineral opal composition SiO 2 × p H 2 O; Earth forms of amorphous silica are diatomitis, trepal (info-free land); An example of artificial amorphous anhydrous silica can serve as silica gel, which is obtained from sodium metasilicate:
Silica gel has a developed surface, and therefore it adsorbs moisture well.
At 1710 °, quartz melts. With rapid cooling of the molten mass consumers, the quartz glass. It has a very small expansion coefficient, due to which the hot quartz glass does not crack with rapid water cooling. From quartz glass produced laboratory dishes and instruments for scientific research.
The simplest formula of silicon oxide (IV) SO 2. similar to carbon oxide formula (IV) withO 2. . Meanwhile, the physical properties of them are sharply different (SiO 2 - solid CO 2 - gas). This difference is explained by the structure of crystal lattices. C0. 2 crystallizes in a molecular grid, SiO 2 - In atomic. StructureSiO 2. The plane image can be represented as follows:
The coordination number of carbon atom in solid CO 2 is 2, and silicon in SiO 2 is 4 equal to 4. Each silicon atom is concluded in a tetrahedron of 4 oxygen atoms. At the same time, the silicon atom is located in the center, and oxygen atoms are located along the tops of the tetrahedron. The whole piece of silica can be considered as a crystal, whose formula (SiO 2) N. This structure of silicon oxide (IV) determines its high hardness and refractory.
By chemical properties of silicon oxide (IV) SiO 2 refers to acid oxides. When fusing it with solid alkalis, silicic acid salts are formed by the main oxides and carbonates:
With silica (IV) oxide, only melic acid interacts:
With this reaction, glass is etched.
In water, silicon oxide (IV) does not dissolve and does not interact with it. Therefore, silicic acid is obtained indirectly, acting with acid at a solution of potassium silicate or sodium:
At the same time, silicic acid (depending on the concentration of the initial solutions of salt and acid) can be obtained both in the form of a study-like mass containing water and in the form of a colloidal solution (sol).
Silicon acids. SiO 2 is an anhydride of a row of silicic acids, the composition of which can be expressed by the general formula XSIO 2 × YH 2 O, where x and y — whole numbers:
1) x \u003d 1, y \u003d 1: sio 2 × h 2 o, i.e. H 2 SiO 3 - methacremium acid;
2) x \u003d 1, y \u003d 2: sio 2 × 2H 2 O, i.e. H 4 SiO 4 - orthocremium acid;
3) h. \u003d 2, y \u003d 1: 2sio 2 × H 2 O, i.e. H 2 Si 2 O 5 - two-strand acid.
Silicic acid is constructed of tetrahedral structural units (in each such link, the silicon atom is located in the center of the tetrahedron, and oxygen atoms are located on the vertices). Structural links, combining in chains, form more stable polycremium acids:
The composition of such a compound can be expressed by the formula (H 2 SiO 3) N. However, usually silicic acid is depicting the formula H 2 SiO 3. H 2 SiO 3 is a very weak, a little soluble in water. When heated, it is easily disintegrated by the same as coalic acid:
All silicic acids are very weak (weaker coal).
Silicates.Salts of all silicic acids call silicates Although, as a rule, in the educational literature under silicates, the salts of methacremium acid are implied. Their composition is usually depicted by the formula in the form of compounds of elements oxides. For example, Casio 3 calcium silicate can be expressed as follows: Sao × SiO 2.
Silicates of the composition R 2 O × NSIO 2, where R 2 O - sodium oxides or potassium, are called soluble glass And their concentrated aqueous solutions - liquid glass. Sodium soluble glass has the greatest value.
When standing on the air, silicate solutions are purified, since carbon monoxide (IV) in the air (IV) displaces silicic acid from its salts:
Silicic acid is practically insoluble in water - this property is used as a high-quality reaction to the SiO 3 ion 2-.
Silicates are obtained by fusion of silicon oxide with alkalis or carbonates:
The use of silicates.Sodium and potassium silicates are most widely used. Concentrated solutions of these salts are called liquid glass;they have a strong masculous reaction due to hydrolysis. Liquid glass is used in the manufacture of glue and waterproof tissues. Liquid glass is used as a binder in the manufacture of acid-resistant concrete, as well as for the manufacture of putty, connecting glue. They are impregnated with fabrics, wood and paper to give them fire resistance and waterproof.
