Silicon: application, chemical and physical properties

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

Silicon is a chemical element

If we characterize this element by position in the periodic system, then we can identify the following important points:

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

Thus, from a chemical point of view, a silicon atom is a sufficiently studied element; its many different properties are described.

Discovery story

Since in nature very different compounds of the element under consideration are very popular and massive in content, from ancient times people used and knew about the properties of precisely many of them. Pure silicon for a long time 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, Rusich, Persians and others) were precious and ornamental stones based on silicon oxide. These include:

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

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

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

Jens Jacobs Berzelius succeeded in successfully obtaining pure silicon in pure form in 1823. To this end, he conducted an experiment on the fusion of silicon fluoride and potassium metal vapor. As a result, I received an amorphous modification of the element in question. The same scientists proposed the Latin name for the open atom.

A little later, in 1855, another scientist - St. Clair-Devill - was able to synthesize another allotropic variety - crystalline silicon. Since then, knowledge about this element and its properties began to replenish very quickly. People realized that it has unique features that can be very wisely used to meet their own needs. Therefore, today one of the most popular elements in electronics and technology is silicon. Its application only expands its borders every year.

The scientist Hess gave the Russian name to the atom in 1831. It is this that has been fixed to this day.

Content in nature

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

Where exactly is silicon?

1. In the deep layers of the soil.
2. In rocks, deposits and massifs.
3. At the bottom of reservoirs, especially the seas and oceans.
4. In plants and marine life of the animal kingdom.
5. In humans and terrestrial animals.

You can identify some of the most common minerals and rocks, in the composition of which a large amount of silicon is present. Their chemistry is such that the mass content of the pure element in them reaches 75%. However, the specific figure depends on the type of material. So, rocks and minerals with a silicon content:

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

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

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

Physical properties of silicon

If we give a characterization of the element under consideration in terms of a set of physicochemical properties, then physical parameters should be designated first. Here are a few basic ones:

1. It exists in the form of two allotropic modifications - amorphous and crystalline, which differ in all properties.
2. The crystal lattice is very similar to that of diamond, because carbon and silicon are almost the same in this respect. However, the distance between the atoms is different (silicon has more), so the diamond is much harder and stronger. The type of lattice is cubic face-centered.
3. The substance is very fragile, at high temperatures it becomes ductile.
4. The melting point is 1415 ° C.
5. Boiling point - 3250˚.
6. The density of the substance is 2.33 g / cm ³ .
7. The color of the compound is silver-gray, a characteristic metallic luster is expressed.
8. It has good semiconductor properties, which can vary with the addition of certain agents.
9. Insoluble in water, organic solvents and acids.
10. Specifically soluble in alkalis.

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

Chemical properties

The chemical properties of silicon are very dependent on the reaction conditions. If we talk about a pure substance with standard parameters, then we need to indicate a very low activity. Both crystalline and amorphous silicon are very inert. Do not interact with strong oxidizing agents (except fluorine), nor 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 is able to form under the influence of water, air, vapors.

If you change the standard conditions and heat silicon to a temperature above 400 ° C, then its chemical activity will increase significantly. In this case, he will react with:

• oxygen;
• all types of halogens;
• hydrogen.

With a further increase in temperature, the formation of products is possible upon interaction with boron, nitrogen, and carbon. Of particular importance is carborundum - SiC, since it is a good abrasive material.

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

• alkaline;
• alkaline earth;
• transition metals.

The compound obtained by the alloying of iron and silicon has unusual properties. It is called ferrosilicon ceramics and is successfully used in industry.

Silicon does not enter into interaction with complex substances, therefore, of all their varieties, it is able to 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 ° C. All this once again confirms the physical basis of the substance - a diamond-like stable crystal lattice, which gives it strength and inertness.

Production methods

Obtaining pure silicon is a rather costly process. 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, simply getting the substance is not enough. It should also be qualitatively cleaned of foreign elements.

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

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

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

Amorphous silicon

The characteristic of silicon will be incomplete if we do not consider each of its allotropic modifications separately. The first of them is amorphous. In this state, the substance under consideration 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 crystalline variety. Its lattice shows that this substance is only a form of finely divided silicon, which exists in the form of crystals. Therefore, as such, these modifications are one and the same compound.

However, their properties differ, therefore it is customary to talk about allotropy. Amorphous silicon itself 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 this form (powder), the compound is easily applied to any surface, whether it is plastic or glass. Therefore, amorphous silicon is so convenient to use. The application is based on the manufacture of solar panels of various sizes.

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

Such a modification is obtained by reducing the compounds with active metals, for example, sodium or magnesium.

Crystalline silicon

Silver-gray brilliant modification of the element in question. It is this form that is the most common and most demanded. This is due to the set of qualitative properties that this substance possesses.

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

1. Electronic quality - the cleanest and highest quality. It is this type that is used in electronics to create particularly sensitive devices.
2. Solar quality. The name itself defines the area of ​​use. It is also a fairly high purity silicon, the use of which is necessary to create high-quality and long-lasting solar cells. Photoelectric converters created on the basis of precisely the crystalline structure are better and more wear-resistant than those created using amorphous modification by spraying onto various types of substrates.
3. Technical silicon. This sample includes those samples of the substance that contain about 98% of the pure element. Everything else goes to various kinds of impurities:

• boron;
• aluminum;
• chlorine;
• carbon;
• phosphorus and others.

The latter variety of the substance in question is used to produce polycrystals of silicon. For this, recrystallization processes are carried out. As a result of this 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 amorphous and crystalline modifications. This option is easier to work with; it is better processed and refined with fluorine and chlorine.

The products that result can be classified as follows:

• multisilicon;
• single crystal;
• shaped crystals;
• silicon scrap
• technical silicon;
• production waste in the form of fragments and debris.

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

The use of pure silicon

Silicon production in industry is well established, and its scale is quite voluminous. 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 and crystalline amorphous silicon used?

1. In metallurgy as an alloying agent, capable of changing the properties of metals and their alloys. So, it is used in the smelting of steel and cast iron.
2. Different types of substances go into the manufacture of a cleaner option - polysilicon.
3. Compounds of silicon with organic substances is an entire chemical industry that has gained particular popularity today. Organosilicon materials are used in medicine, in the manufacture of dishes, tools and much more.
4. Making various solar panels. This method of generating energy is one of the most promising in the future. Environmentally friendly, cost-effective and wear-resistant - the main advantages of this generation of electricity.
5. Silicon for lighters has been used for a very long time. Even in antiquity, people used flint to produce sparks when lighting a fire. This principle is the basis for the production of various kinds of lighters. Today, there are species in which flint is replaced with an alloy of a certain composition, which gives an even faster result (sparking).
6. Electronics and solar energy.
7. Making 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.

The use of silicon compounds

In addition to a simple substance, various silicon compounds are 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 what are they made of?

1. Quartz, or river sand - SiO ₂ . Used for the manufacture of building and decorative materials such as cement and glass. Where these materials are used, everyone knows. No construction is complete without these components, which confirms the importance of silicon compounds.
2. Silicate ceramics, which include materials such as earthenware, porcelain, brick and products based on them. These components are used in medicine, in the manufacture of dishes, decorative jewelry, household items, in construction and other domestic areas of human activity.
3. Organosilicon compounds - silicones, silica gels, silicone oils.
4. Silicate glue - used as clerical, in pyrotechnics and construction.

Silicon, the price of which varies on the world market, but does not cross the mark of 100 Russian rubles per kilogram (per crystalline) from top to bottom, is a sought-after 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 mortally dangerous 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. Animal experiments have shown that those individuals that consume enough silicon daily grow better.