Chemical properties of silicon and its compounds. Interaction of silicon with simple substances. Silicic acid. Silicates

As an independent chemical element, silicon became known to mankind only in 1825. That, of course, did not prevent the use of silicon compounds in such a number of spheres that it is easier to list those where the element is not used. This article will shed light on the physical, mechanical and useful chemical properties of silicon and its compounds, applications, and we will also talk about how silicon affects the properties of steel and other metals.

First, let's focus on the general characteristics of silicon. From 27.6 to 29.5% of the mass of the earth's crust is silicon. In seawater, the concentration of the element is also hefty - up to 3 mg / l.

Silicon occupies the second place of honor in the lithosphere after oxygen. However, its most famous form, silica, is dioxide, and it is its properties that have become the basis for such widespread use.

This video will tell you what silicon is:

Concept and features

Silicon is a non-metal, but under different conditions it can exhibit both acidic and basic properties. It is a typical semiconductor and is widely used in electrical engineering. Its physical and chemical properties are largely determined by the allotropic state. Most often they deal with the crystalline form, since its qualities are more in demand in the national economy.

Silicon is one of the basic macronutrients in the human body. Its lack has a detrimental effect on the condition of bone tissue, hair, skin, nails. In addition, silicon affects the performance of the immune system.
In medicine, the element, or rather, its compounds, found their first application in this capacity. Water from wells lined with silicon differed not only in purity, but also had a positive effect on resistance to infectious diseases. Today, a compound with silicon serves as the basis for drugs against tuberculosis, atherosclerosis, and arthritis.
In general, the non-metal is inactive, however, it is difficult to find it in its pure form. This is due to the fact that in air it is quickly passivated by a layer of dioxide and stops reacting. When heated, the chemical activity increases. As a result, humanity is much more familiar with the compounds of the substance, and not with itself.

So, silicon forms alloys with almost all metals - silicides. All of them differ in their refractoriness and hardness and are used in the respective areas: gas turbines, furnace heaters.

The non-metal is placed in the table of D.I.Mendeleev in group 6 together with carbon, germanium, which indicates a certain commonality with these substances. So, with carbon it is "related" by the ability to form compounds of the type of organic. At the same time, silicon, like germanium, can show the properties of a metal in some chemical reactions, which is used in synthesis.

Pros and cons

Like any other substance from the point of view of application in the national economy, silicon has certain useful or not very good qualities. They are important precisely for determining the scope of use.

A considerable advantage of the substance is its availability... In nature, it is true, it is not in a free form, but nevertheless, the technology for producing silicon is not so complicated, although it is energy-intensive.
The second most important advantage is formation of many compounds with unusually useful properties. These are silanes, and silicides, and dioxide, and, of course, various silicates. The ability of silicon and its compounds to form complex solid solutions is practically endless, which allows endless production of a wide variety of glass, stone and ceramics.
Semiconductor properties non-metal provides it with a place as a base material in electrical and radio engineering.
Non-metal is non-toxic, which allows application in any industry, and at the same time does not turn the technological process into a potentially hazardous one.

The disadvantages of the material include only relative fragility with good hardness. Silicon is not used for supporting structures, but this combination allows the crystal surface to be properly processed, which is important for instrumentation.

Let's now talk about the basic properties of silicon.

Properties and characteristics

Since crystalline silicon is most often used in industry, it is precisely its properties that are more important, and it is they that are given in the technical characteristics. The physical properties of the substance are as follows:

melting point - 1417 C;
boiling point - 2600 C;
the density is 2.33 g / cc. cm, which indicates fragility;
the heat capacity, as well as the thermal conductivity, are not constant even in the purest samples: 800 J / (kg K), or 0.191 cal / (g deg) and 84-126 W / (m K), or 0.20-0, 30 cal / (cm · sec · deg), respectively;
transparent to long-wave infrared radiation, which is used in infrared optics;
dielectric constant - 1.17;
hardness on the Mohs scale - 7.

The electrical properties of a non-metal are highly dependent on impurities. In industry, this feature is used by modulating the desired type of semiconductor. At normal temperatures, silicon is brittle, but when heated above 800 C, plastic deformation is possible.

The properties of amorphous silicon are strikingly different: it is highly hygroscopic, it reacts much more actively even at normal temperature.

The structure and chemical composition, as well as the properties of silicon, are discussed in the video below:

Composition and structure

Silicon exists in two allotropic forms, which are equally stable at normal temperatures.

Crystal looks like a dark gray powder. The substance, although it has a diamond-like crystal lattice, is fragile due to the excessively long bond between atoms. Its properties of a semiconductor are of interest.
At very high pressures, you can get hexagonal modification with a density of 2.55 g / cc. see However, this phase has not yet found practical significance.
Amorphous - brown-brown powder. In contrast to the crystalline form, it reacts much more actively. This is due not so much to the inertness of the first form as to the fact that in air the substance is covered with a layer of dioxide.

In addition, it is necessary to take into account another type of classification associated with the size of the silicon crystal, which together form the substance. The crystal lattice, as you know, presupposes the ordering not only of the atoms, but also of the structures that these atoms form - the so-called long-range order. The larger it is, the more homogeneous in properties the substance will be.

Monocrystalline - the sample is one crystal. Its structure is maximally ordered, its properties are uniform and well predictable. It is this material that is most in demand in electrical engineering. However, it also belongs to the most expensive species, since the process of obtaining it is complicated, and the growth rate is low.
Multicrystalline - the sample contains a number of large crystal grains. The boundaries between them form additional defect levels, which reduces the performance of the sample as a semiconductor and leads to faster wear. The technology for growing a multicrystal is simpler, and therefore the material is cheaper.
Polycrystalline - consists of a large number of grains located randomly relative to each other. This is the purest type of industrial silicon, used in microelectronics and solar energy. Quite often it is used as a raw material for growing multi- and single crystals.
Amorphous silicon also occupies a separate position in this classification. Here, the order of arrangement of atoms is maintained only at the shortest distances. However, in electrical engineering, it is still used in the form of thin films.

Non-metal production

It is not so easy to obtain pure silicon, given the inertness of its compounds and the high melting points of most of them. In industry, carbon reduction from dioxide is most often resorted to. The reaction is carried out in arc furnaces at a temperature of 1800 C. Thus, a non-metal with a purity of 99.9% is obtained, which is not enough for its use.

The resulting material is chlorinated in order to obtain chlorides and hydrochlorides. Then the compounds are purified from impurities by all possible methods and reduced with hydrogen.

The substance can also be purified by obtaining magnesium silicide. The silicide is exposed to hydrochloric or acetic acid. Silane is obtained, and the latter is purified by various methods - sorption, rectification, and so on. Then the silane is decomposed into hydrogen and silicon at a temperature of 1000 C. In this case, a substance is obtained with an impurity fraction of 10 -8 -10 -6%.

Application of the substance

For industry, the most interesting are the electrophysical characteristics of a non-metal. Its single-crystal form is an indirect-gap semiconductor. Its properties are determined by impurities, which makes it possible to obtain silicon crystals with desired properties. Thus, the addition of boron and indium makes it possible to grow a crystal with hole conductivity, and the introduction of phosphorus or arsenic makes it possible to grow a crystal with electronic conductivity.

Silicon is literally the foundation of modern electrical engineering. Transistors, photocells, integrated circuits, diodes and so on are made from it. Moreover, the functionality of the device is almost always determined only by the near-surface layer of the crystal, which determines very specific requirements for the surface treatment.
In metallurgy, technical silicon is used both as a modifier for alloys - it gives greater strength, and as a component - in, for example, and as a deoxidizer - in the production of cast iron.
Ultrapure and refined metallurgical forms the basis of solar energy.
Non-metal dioxide occurs naturally in very different forms. Its crystalline varieties - opal, agate, carnelian, amethyst, rock crystal - have found their place in jewelry. Not so attractive outwardly modifications - flint, quartz, are used in metallurgy, and in construction, and in radioelectronics.
The compound of a non-metal with carbon - carbide, is used in metallurgy, and in instrument making, and in the chemical industry. It is a wide-gap semiconductor, has a high hardness - 7 on the Mohs scale, and strength, which allows it to be used as an abrasive material.
Silicates - that is, silicic acid salts. Unstable, easily decomposed by temperature. They are remarkable in that they form numerous and varied salts. But the latter are the basis for the production of glass, ceramics, faience, crystal, etc. We can safely say that modern construction is based on a variety of silicates.
Glass is the most interesting case here. It is based on aluminosilicates, but negligible impurities of other substances - usually oxides, give the material a lot of different properties, including color. -, faience, porcelain, in fact, has the same formula, albeit with a different ratio of components, and its diversity is also amazing.
Non-metal has another ability: it forms compounds like carbon, in the form of a long chain of silicon atoms. Such compounds are called organosilicon compounds. The scope of their application is no less well-known - these are silicones, sealants, lubricants, and so on.

Silicon is a very common element and is of extraordinary importance in very many areas of the national economy. Moreover, not only the substance itself is actively used, but all its various and numerous compounds.

This video will tell you about the properties and uses of silicon:

One of the most common elements in nature is silicium, or silicon. Such a wide distribution speaks of the importance and significance of this substance. This was quickly understood and learned by people who learned how to use silicon for their own purposes. Its use is based on special properties, which we will talk about further.

Silicon - a chemical element

If you characterize this element by position in the periodic system, then the following important points can be identified:

The serial number is 14.
The period is the third minor.
Group - IV.
The subgroup is the main one.
The structure of the outer electron shell is expressed by the formula 3s 2 3p 2.
The element silicon is designated by the chemical symbol Si, which is pronounced "silicium".
The oxidation states it exhibits: -4; +2; +4.
The valency of the atom is IV.
The atomic mass of silicon is 28.086.
In nature, there are three stable isotopes of this element with mass numbers 28, 29 and 30.

Thus, from a chemical point of view, the silicon atom is a sufficiently studied element, and many of its different properties have been described.

Discovery history

Since in nature it is the various compounds of the element in question that are very popular and massive in content, since ancient times people have used and knew about the properties of just many of them. For a long time, pure silicon remained beyond human knowledge in chemistry.

The most popular compounds used in everyday life and industry by the peoples of ancient cultures (Egyptians, Romans, Chinese, Rusichi, Persians and others) were precious and semi-precious stones based on silicon oxide. These include:

opal;
rhinestone;
topaz;
chrysoprase;
onyx;
chalcedony and others.

It is also customary to use quartz in the construction business since ancient times. However, elemental silicon itself remained undiscovered until the 19th century, although many scientists tried in vain to isolate it from various compounds, using catalysts, high temperatures, and even electric current for this. These are such bright minds as:

Karl Scheele;
Gay Lussac;
Thenar;
Humphrey Davy;
Antoine Lavoisier.

Jens Jacobs Berzelius succeeded in successfully obtaining silicon in its pure form in 1823. For this, he conducted an experiment on fusion of vapors of silicon fluoride and metallic potassium. As a result, an amorphous modification of the element in question was obtained. The same scientist proposed the Latin name for the open atom.

A little later, in 1855, another scientist - Saint Clair-Deville - managed to synthesize another allotropic variety - crystalline silicon. Since then, knowledge about this element and its properties began to grow very quickly. People realized that it has unique features that can be very competently used to meet their own needs. Therefore, today one of the most demanded elements in electronics and technology is silicon. Its application only expands its boundaries every year.

The Russian name for the atom was given by the scientist Hess in 1831. This is what has been entrenched to this day.

Silicon is the second most abundant in nature after oxygen. Its percentage in comparison with other atoms in the earth's crust is 29.5%. In addition, carbon and silicon are two special elements that can form chains by connecting with each other. That is why more than 400 different natural minerals are known for the latter, in the composition of which it is contained in the lithosphere, hydrosphere and biomass.

Where exactly is silicon found?

In deep soil layers.
In rocks, deposits and massifs.
At the bottom of water bodies, especially seas and oceans.
In plants and marine life in the animal kingdom.
In humans and land animals.

Several of the most common minerals and rocks can be identified, in which silicon is present in large quantities. Their chemistry is such that the mass content of the pure element in them reaches 75%. However, the exact figure depends on the type of material. So, rocks and minerals with silicon content:

feldspars;
mica;
amphiboles;
opals;
chalcedony;
silicates;
sandstones;
aluminosilicates;
clays and others.

Accumulating in the shells and outer skeletons of marine animals, silicon over time forms powerful deposits of silica at the bottom of water bodies. It is one of the natural sources of this element.

In addition, it was found that silicium can exist in a pure native state - in the form of crystals. But such deposits are very rare.

Physical properties of silicon

If you give a characteristic of the element under consideration by a set of physicochemical properties, then first of all it is the physical parameters that should be designated. Here are some of the main ones:

It exists in the form of two allotropic modifications - amorphous and crystalline, which differ in all properties.
The crystal lattice is very similar to that of diamond, because carbon and silicon are practically the same in this respect. However, the distance between atoms is different (silicon has more), so diamond is much harder and stronger. Lattice type - face-centered cubic.
The substance is very fragile; it becomes plastic at high temperatures.
The melting point is 1415˚С.
The boiling point is 3250˚С.
The density of the substance is 2.33 g / cm 3.
The color of the compound is silvery-gray, with a characteristic metallic luster.
It has good semiconducting properties, which can be varied with the addition of certain agents.
Insoluble in water, organic solvents and acids.
Soluble in alkalis.

The indicated physical properties of silicon allow people to manipulate it and use it to create various products. So, for example, the use of pure silicon in electronics is based on the properties of semiconductor.

Chemical properties

The chemical properties of silicon are highly dependent on the reaction conditions. If we talk about the standard parameters, then you need to designate a very low activity. Both crystalline and amorphous silicon are very inert. They do not interact with strong oxidizing agents (except fluorine) or with strong reducing agents.

This is due to the fact that an oxide film of SiO 2 is instantly formed on the surface of the substance, which prevents further interactions. It can form under the influence of water, air, vapors.

If the standard conditions are changed and silicon is heated to a temperature above 400 ° C, then its chemical activity will greatly increase. In this case, it will react with:

oxygen;
all types of halogens;
hydrogen.

With a further increase in temperature, the formation of products is possible when interacting with boron, nitrogen and carbon. Carborundum - SiC is of particular importance, as it is a good abrasive material.

Also, the chemical properties of silicon are clearly visible in reactions with metals. In relation to them, it is an oxidizing agent, therefore the products are called silicides. Similar compounds are known for:

alkaline;
alkaline earth;
transition metals.

The compound obtained by fusing iron and silicon possesses unusual properties. It is called ferrosilicon ceramics and is successfully used in industry.

Silicon does not interact with complex substances, therefore, of all their varieties, it can dissolve only in:

aqua regia (a mixture of nitric and hydrochloric acids);
caustic alkalis.

In this case, the temperature of the solution should be at least 60˚С. All this once again confirms the physical basis of the substance - a diamond-like stable crystal lattice, which gives it strength and inertness.

Methods of obtaining

Obtaining silicon in its pure form is a rather costly process economically. In addition, due to its properties, any method gives only 90-99% pure product, while impurities in the form of metals and carbon remain all the same. Therefore, just getting the substance is not enough. It should also be cleaned of foreign elements qualitatively.

In general, silicon production is carried out in two main ways:

From white sand, which is pure silicon oxide SiO 2. When it is calcined with active metals (most often with magnesium), a free element is formed in the form of an amorphous modification. The purity of this method is high, the product is obtained with a 99.9% yield.
A more widespread method on an industrial scale is the sintering of molten sand with coke in specialized thermal kilns. This method was developed by the Russian scientist N.N. Beketov.

Further processing consists in subjecting the products to cleaning methods. For this, acids or halogens (chlorine, fluorine) are used.

Amorphous silicon

The characterization of silicon will be incomplete if we do not consider separately each of its allotropic modifications. The first of these is amorphous. In this state, the substance we are considering is a brown-brown powder, finely dispersed. It has a high degree of hygroscopicity, exhibits a fairly high chemical activity when heated. Under standard conditions, it can interact only with the strongest oxidizing agent - fluorine.

It is not entirely correct to call amorphous silicon a kind of crystalline silicon. Its lattice shows that this substance is only a form of finely dispersed silicon, existing in the form of crystals. Therefore, as such, these modifications are one and the same compound.

However, their properties differ, and therefore it is customary to speak of allotropy. By itself, amorphous silicon has a high light absorption capacity. In addition, under certain conditions, this indicator is several times higher than that of the crystalline form. Therefore, it is used for technical purposes. In the form under consideration (powder), the compound is easily applied to any surface, be it plastic or glass. That is why amorphous silicon is so convenient for use. Application is based on different sizes.

Although the wear of batteries of this type is quite fast, which is associated with abrasion of a thin film of the substance, however, the use and demand is only growing. Indeed, even in a short service life, solar cells based on amorphous silicon are able to provide energy to entire enterprises. In addition, the production of such a substance is waste-free, which makes it very economical.

This modification is obtained by reduction of compounds with active metals, for example sodium or magnesium.

Crystalline silicon

A silvery-gray shiny modification of the element in question. It is this form that is the most common and most popular. This is due to the set of qualitative properties possessed by this substance.

The characteristic of silicon with a crystal lattice includes the classification of its types, since there are several of them:

Electronic quality - the purest and highest quality. This type is used in electronics to create especially sensitive devices.
Sunny quality. The name itself defines the area of \u200b\u200buse. It is also sufficiently high in purity silicon, the use of which is necessary to create high-quality and long-lasting solar cells. Photovoltaic converters based on the crystal structure are of higher quality and wear-resistant than those created using amorphous modification by sputtering on various types of substrates.
Technical silicon. This variety includes those samples of a substance that contain about 98% of a pure element. Everything else goes to various kinds of impurities:

aluminum;
chlorine;
carbon;
phosphorus and others.

The latter type of the substance under consideration is used to obtain silicon polycrystals. For this, recrystallization processes are carried out. As a result, in terms of purity, such products are obtained that can be attributed to the groups of solar and electronic quality.

By its nature, polysilicon is an intermediate product between the amorphous and crystalline modification. This option is easier to work with, it is better processed and purified by fluorine and chlorine.

The resulting products can be classified as follows:

multi-silicon;
monocrystalline;
profiled crystals;
silicon scrap;
technical silicon;
production waste in the form of fragments and scraps of matter.

Each of them finds application in industry and is fully used by man. Therefore, those concerning silicon are considered waste-free. This significantly reduces its economic cost, while not affecting quality.

Using pure silicon

The production of silicon in industry is well established, and its scale is quite large. This is due to the fact that this element, both pure and in the form of various compounds, is widespread and in demand in various branches of science and technology.

Where is pure crystalline and amorphous silicon used?

In metallurgy as an alloying additive capable of changing the properties of metals and their alloys. So, it is used in the smelting of steel and iron.
Different types of substances are spent on the manufacture of a cleaner version - polysilicon.
Silicon compounds with - this is a whole chemical industry that has gained particular popularity today. Organosilicon materials are used in medicine, in the manufacture of dishes, tools and much more.
Manufacturing of various solar panels. This method of obtaining energy is one of the most promising in the future. Eco-friendly, cost-effective and hardwearing - the main advantages of such electricity.
Silicon for lighters has been around for a long time. Even in ancient times, people used flint to generate a spark when lighting a fire. This principle is the basis for the production of lighters of various kinds. Today there are species in which the flint is replaced by an alloy of a certain composition, which gives an even faster result (sparking).
Electronics and solar energy.
Manufacturing of mirrors in gas laser devices.

Thus, pure silicon has a lot of advantageous and special properties that allow it to be used to create important and necessary products.

Application of silicon compounds

In addition to a simple substance, various silicon compounds are also used, and very widely. There is a whole industry called silicate. It is she who is based on the use of various substances, which include this amazing element. What are these compounds and which of them are produced?

Quartz, or river sand - SiO 2. It is used to make building and decorative materials such as cement and glass. Everyone knows where these materials are used. No construction is complete without these components, which confirms the importance of silicon compounds.
Silicate ceramics, which includes materials such as earthenware, porcelain, bricks and products based on them. These components are used in medicine, in the manufacture of dishes, decorative ornaments, household items, in construction and other household areas of human activity.
- silicones, silica gels, silicone oils.
Silicate glue - used as stationery, in pyrotechnics and construction.

Silicon, the price of which varies on the world market, but does not cross from top to bottom the mark of 100 rubles per kilogram (per crystalline), is a demanded and valuable substance. Naturally, the compounds of this element are also widespread and applicable.

The biological role of silicon

From the point of view of importance for the body, silicon is important. Its content and distribution in tissues is as follows:

0.002% - muscle;
0.000017% - bone;
blood - 3.9 mg / l.

Every day, about one gram of silicon should get inside, otherwise diseases will begin to develop. There are no fatal ones among them, however, prolonged silicon starvation leads to:

hair loss;
the appearance of acne and acne;
fragility and fragility of bones;
easy capillary permeability;
fatigue and headaches;
the appearance of numerous bruises and bruises.

For plants, silicon is an important trace element necessary for normal growth and development. Experiments on animals have shown that those individuals who daily consume a sufficient amount of silicon grow better.

Coal is most often found in nature. Graphite deposits are often found. It is a more stable allotropic modification than diamond, so there is more of it in the earth's crust than diamond. Graphite occurs in the ground in the form of flaky and lamellar masses. Scientists believe that it was formed from coal under the influence of high pressure. Diamonds are rare. They are believed to be formed from carbonaceous substances at high temperatures and pressures at a depth of about 100 km.

The use of carbon and its compounds

1) First, diamonds are only used for the production of diamonds, which have always been appreciated as the most expensive jewelry.

The high hardness of diamonds allows them to be used for the manufacture of drilling and cutting tools, processing other stones, metals, and hard materials. Diamond drills are used to drill concrete slabs. With the help of a diamond tool, it is possible to process stones used in watch movements with high precision. Thin diamond plates are applied to surgical instruments. The use of diamond in technology reduces the cost and accelerates production processes.

Graphite is widely used in technology and industry. Heat resistance and chemical inertness make it an irreplaceable material for the manufacture of refractory products, as well as chemically resistant pipes and apparatus.

In the electrical industry, the electrical conductivity of graphite is used. Electrodes, galvanic cells, contacts of electrical machines are made of it. Graphite has great resistance. Therefore, heaters for electric furnaces are made from it.

Very pure graphite is used in nuclear reactors.

Graphite serves as pencil rods. Due to the flaking of the flakes, the core leaves a mark on the paper.

Bituminous coal is used as fuel. It is processed into coke, which contains fewer impurities than coal.

Coke is a good reducing agent; it is used in the metallurgical industry to obtain metals.

2) Carbon dioxide is used as a refrigerant, used in extinguishing fires, used in medicine. It is added to the oxygen that seriously ill patients breathe. Carbon dioxide is consumed in the preparation of soda and other drinks.

3) The most widely used is calcium carbonate. Quicklime used in construction is obtained from it. Sodium carbonates (soda) and potassium (potash) are used in soap making, for glass production, in the pharmaceutical industry, for the production of fertilizers.

Silicon

Silicon is no less important in nature and human life than carbon. If carbon forms the substances of living nature, then silicon is the basis of the substances that make up the entire planet Earth.

The use of silicon and its compounds

1) Since silicon is a good reducing agent, it is used to obtain metals in the metallurgical industry.

Silicon is used in electronics due to its ability to conduct electric current under certain conditions. Silicon is used to make photocells, semiconductor devices for the production of radios, televisions, and computers.

A brief comparative characteristic of the elements carbon and silicon is presented in table 6.

Table 6

Comparative characteristics of carbon and silicon

Comparison criteria	Carbon - C	Silicon - Si
position in the periodic table of chemical elements	, 2nd period, IV group, main subgroup	, 3rd period, IV group, main subgroup
electronic configuration of atoms
valence capabilities	II - in a stationary state IV - in an excited state
possible oxidation states	, , , , ,	,
higher oxide	, acidic	, acidic
higher hydroxide	- weak unstable acid	() or - weak acid, has a polymer structure
hydrogen compound	- methane (hydrocarbon)	- silane, unstable

Carbon... Allotropy is characteristic of the carbon element. Carbon exists in the form of the following simple substances: diamond, graphite, carbyne, fullerene, of which only graphite is thermodynamically stable. Coal and soot can be viewed as amorphous varieties of graphite.

Graphite is refractory, low volatility, chemically inert at ordinary temperatures, it is an opaque, soft substance, weakly conducting current. The structure of graphite is layered.

Alamaz is an extremely hard, chemically inert (up to 900 ° C) substance, does not conduct current and does not conduct heat well. The structure of a diamond is tetrahedral (each atom in a tetrahedron is surrounded by four atoms, etc.). Therefore, diamond is the simplest polymer, the macromolecule of which consists of some carbon atoms.

Carbyne has a linear structure (–carbyne, polyyne) or (–carbyne, polyene). It is a black powder with semiconducting properties. Under the influence of light, the electrical conductivity of carbine increases, and at a temperature carbyne turns into graphite. Chemically more active than graphite. Synthesized in the early 60-ies of XX century., Later it was found in some meteorites.

Fullerene is an allotropic modification of carbon, formed by molecules that have a "soccer ball" structure. Molecules and other fullerenes were synthesized. All fullerenes are closed structures of carbon atoms in a hybrid state. Unhybridized bond electrons are delocalized as in aromatic compounds. Fullerene crystals are of the molecular type.

Silicon... For silicon, bonds are not characteristic, existence in a hybrid state is not characteristic. Therefore, there is only one stable allotropic modification of silicon, the crystal lattice of which is similar to that of diamond. Silicon - hard (on the Mohs scale hardness is 7), refractory ( ), a very fragile substance of dark gray color with a metallic luster under standard conditions - a semiconductor. Reactivity depends on the size of the crystals (coarse crystalline is less active than amorphous).

The reactivity of carbon depends on the allotropic modification. Carbon in the form of diamond and graphite is quite inert, resistant to acids and alkalis, which makes it possible to make crucibles, electrodes, etc. from graphite. Carbon exhibits a higher reactivity in the form of coal and soot.

Crystalline silicon is rather inert, in amorphous form it is more active.

The main types of reactions reflecting the chemical properties of carbon and silicon are shown in Table 7.

Table 7

Basic chemical properties of carbon and silicon

reaction with	carbon	reaction with	silicon
simple substances	oxygen		oxygen
halogens		halogens
gray		carbon
hydrogen		hydrogen	does not react
metals		metals
complex substances	metal oxides		alkalis
water vapor		acids	does not react
acids

Binders

Binders – mineral or organic building materials used for the manufacture of concrete, fastening individual elements of building structures, waterproofing, etc..

Mineral binders (MVM) - finely ground powdery materials (cements, gypsum, lime, etc.), which, when mixed with water (in some cases, with solutions of salts, acids, alkalis), form a plastic workable mass that solidifies into a strong stone-like body and binds particles of solid aggregates and reinforcement into a monolithic whole.

MWM hardens due to dissolution processes, the formation of a supersaturated solution and colloidal mass; the latter partially or completely crystallizes.

MVM classification:

1.hydraulic binders:

When mixed with water (mixing) they harden and continue to retain or build up their strength in water. These include various cements and hydraulic lime. When hydraulic lime hardens, CaO interacts with water and carbon dioxide in the air and crystallizes the resulting product. They are used in the construction of ground, underground and hydrotechnical structures exposed to constant water exposure.

2.Air-based binders:

When mixed with water, they harden and retain their strength only in air. These include air lime, gypsum-anhydrite and magnesia air binders.

3.acid-resistant binders:

They consist mainly of acid-resistant cement containing a finely ground mixture of quartz sand and; they are sealed, as a rule, with aqueous solutions of sodium or potassium silicate; they retain their strength for a long time when exposed to acids. A reaction takes place during hardening. Used for the production of acid-resistant cements, mortars and concretes in the construction of chemical plants.

4.Autoclaved binders:

They consist of lime-silica and lime-nepheline binders (lime, quartz sand, nepheline sludge) and harden when processed in an autoclave (6-10 hours, steam pressure 0.9-1.3 MPa). They also include sandy Portland cements and other binders based on lime, ash and low-activity sludge. Used in the manufacture of concrete silicate (blocks, bricks and silicate al.).

5.phosphate binders:

Consist of special cements; they are sealed with phosphoric acid with the formation of a plastic mass that gradually solidifies into a monolithic body and retains its strength at temperatures above 1000 ° C. Usually used titanium phosphate, zinc phosphate, aluminophosphate and other cements. They are used for the manufacture of refractory lining mass and sealants for high-temperature protection of metal parts and structures in the production of refractory concrete, etc.

Organic binders (OBM) - substances of organic origin, capable of passing from a plastic state to a solid or low-plastic state as a result of polymerization or polycondensation.

Compared to MVM, they are less brittle and have higher tensile strength. These include products formed during oil refining (asphalt, bitumen), products of thermal decomposition of wood (tar), as well as synthetic thermosetting polyester, epoxy, phenol-formaldehyde resins. They are used in the construction of roads, bridges, floors of industrial premises, roll roofing materials, asphalt-polymer concrete, etc.

Description and properties of silicon

Silicon - element, fourth group, third period in the table of elements. Atomic number 14. Silicon formula- 3s2 3p2. Defined as an element in 1811, and in 1834 it received the Russian name "silicon", instead of the former "Sicily". Melts at 1414 ° C, boils at 2349 ° C.

In molecular structure, it resembles, but inferior to it in hardness. Quite fragile, in a heated state (at least 800º C) acquires plasticity. Translucent infrared radiation. Monocrystalline type of silicon has semiconducting properties. According to some characteristics silicon atomsimilar to the atomic structure of carbon. Silicon electrons have the same valence number as in the carbon structure.

Workers silicon properties depend on the content of certain contents in it. Silicon has a different type of conductivity. In particular, these are "hole" and "electronic" types. To obtain the first, boron is added to silicon. If you add phosphorus, silicon acquires the second type of conductivity. If silicon is heated together with other metals, specific compounds are formed, called "silicides", for example, in the reaction " magnesium-silicon«.

Silicon used for the needs of electronics is primarily assessed by the characteristics of its upper layers. Therefore, it is necessary to pay attention precisely to their quality, it directly affects the overall performance. The operation of the manufactured device depends on them. To obtain the most acceptable characteristics of the upper layers of silicon, they are treated with various chemical methods or irradiated.

Compound "Sulfur-silicon", forms silicon sulfide, which readily interacts with water and oxygen. When reacting with oxygen, at temperatures above 400 ° C, it turns out silica. At the same temperature, reactions with chlorine and iodine, as well as with bromine, become possible, during which volatile substances - tetrahalides are formed.

It will not work to combine silicon and hydrogen by direct contact, for this there are methods of an indirect nature. At 1000 ° C, a reaction with nitrogen and boron is possible, thus obtaining silicon nitride and boride. At the same temperature, by combining silicon with carbon, one can produce silicon carbide, the so-called "carborundum". This composition has a solid structure, the chemical activity is sluggish. Used as an abrasive.

In conjunction with iron, silicon forms a special mixture, this allows the melting of these elements, in which a ferrosilicon ceramic is formed. Moreover, its melting point is much lower than if they were melted separately. At temperatures above 1200 ° C, the element begins to form silicon oxide, also under certain conditions it turns out silicon hydroxide... When etching silicon, water-based alkaline solutions are used. Their temperature should be at least 60 ° C.

Deposits and mining of silicon

Element - the second most common on the planet substance. Silicon makes up almost a third of the volume of the earth's crust. Only oxygen is more common. Advantageously expressed by silica - a compound inherently containing silica. The main derivatives of silicon dioxide are flint, various sands, quartz, as well as field. They are followed by silicate silicon compounds. Nativeness is rare for silicon.

Silicon Applications

Silicon, chemical properties which determine the scope of its application, is divided into several types. Less pure silicon is used for metallurgical needs: for, for example, for adding to aluminum, silicon actively changes its properties, deoxidizers, etc. It actively modifies the properties of metals by adding composition. Silicon alloy them by changing workers characteristics, silicon a very small amount is sufficient.

Also, higher-quality derivatives are produced from crude silicon, in particular, mono and polycrystalline silicon, as well as silicon organics - these are silicones and various organic oils. It has also found its way into the cement and glass industries. He did not bypass brick production, factories producing porcelain and also cannot do without it.

Silicon is part of the well-known silicate glue, which is used for repair work, and before it was used in office needs, until more practical substitutes appeared. Some pyrotechnic products also contain silicon. Hydrogen can be obtained from it and its iron alloys in the open air.

What goes better silicon? Plate solar panels also include silicon, naturally not technical. For these needs, silicon of ideal purity or at least technical silicon of the highest purity is required.

So-called "Electronic silicon" which contains almost 100% silicon, has much better performance. Therefore, it is preferred in the production of ultra-precise electronic devices and complex microcircuits. Their manufacture requires a high-quality production circuit, siliconfor which only the highest category should go. The operation of these devices depends on how much contains silicon unwanted impurities.

Silicon occupies an important place in nature, and most living beings constantly need it. For them, it is a kind of building composition, because it is extremely important for the health of the musculoskeletal system. A person absorbs up to 1 g daily silicon compounds.

Could silicon be harmful?

Yes, for the reason that silicon dioxide is extremely dusty. It has an irritating effect on the mucous surfaces of the body and can actively accumulate in the lungs, causing silicosis. For this, in the production of silicon cells associated with the processing, the use of respirators is mandatory. Their presence is especially important when it comes to silicon monoxide.

Silicon price

As you know, all modern electronic equipment, from telecommunications to computer technology, is based on the use of silicon, using its semiconductor properties. Its other analogues are used to a much lesser extent. The unique properties of silicon and its derivatives are so far out of competition, for many years to come. Despite the decline in prices in 2001, silicon, sales quickly bounced back. And already in 2003 the trade turnover amounted to 24 thousand tons per year.

For the latest technologies, requiring almost crystalline silicon purity, its technical counterparts are not suitable. And due to its complex cleaning system, the price increases accordingly. The more common is the polycrystalline type of silicon; its monocrystalline prototype is in somewhat less demand. At the same time, the share of using silicon for semiconductors occupies the lion's share of the turnover.

Product prices vary depending on purity and purpose silicon, buy which, you can start from 10 cents per kg of crude raw materials and up to $ 10 and more for "electronic" silicon.