Chemical properties of tungsten. Characteristics and applications of tungsten

Tungsten is a chemical element of the periodic system of Mendeleev, which belongs to the VI group. In nature, tungsten occurs as a mixture of five isotopes. In its usual form and under normal conditions it is a solid metal of a silvery-gray color. It is also the most refractory of all metals.

Basic properties of tungsten

Tungsten is a metal that has remarkable physical and chemical properties. Almost all branches of modern production use tungsten. Its formula is usually expressed in the form of a metal oxide - WO ₃ . Tungsten is considered the most refractory of metals. It is assumed that only siborgy can be even more refractory. But for now, for the time being, this can not be asserted, since the siborgy has a very short time of existence.

This metal has special physical and chemical properties. Tungsten has a density of 19300 kg / m ³ , its melting point is 3410 ° C. In this parameter, it takes the second place after carbon - graphite or diamond. In nature, tungsten is found in the form of five stable isotopes. Their mass numbers are in the range from 180 to 186. Tungsten has the 6th valence, and in the compounds it can be 0, 2, 3, 4 and 5. The metal also has a sufficiently high level of thermal conductivity. For tungsten, this figure is 163 W / (m * deg). By this property, it exceeds even such compounds as aluminum alloys. The mass of tungsten is due to its density, which is equal to 19 kg / m ³ . The degree of oxidation of tungsten varies from +2 to +6. In the higher degrees of its oxidation the metal has acid properties, and in the lower ones - the basic properties.

In this case alloys of lower tungsten compounds are considered unstable. The most persistent are compounds with a degree of +6. They exhibit the most characteristic chemical properties for the metal. Tungsten has the property of easily forming complexes. But metallic tungsten is usually very resistant. It begins to interact with oxygen only at a temperature of +400 ° C. The crystal lattice of tungsten refers to the type of cubic body-centered.

Interaction with other chemicals

If tungsten is mixed with dry fluorine, it is possible to obtain a compound called "hexafluoride", which melts already at a temperature of 2.5 ° C, and boils at 19.5 ° C. A similar substance is obtained by combining tungsten with chlorine. But for such a reaction, a sufficiently high temperature is necessary, of the order of 600 ° C. However, the substance easily resists the destructive effect of water and practically does not undergo changes in the cold. Tungsten is a metal which, without oxygen, does not produce a dissolution reaction in alkalis. However, it dissolves readily in a mixture of HNO ₃ and HF. The most important of the chemical compounds of tungsten are its trioxide WO ₃ , H ₂ WO ₄ - tungstic acid, as well as its derivatives - tungstate salts.

We can consider some chemical properties of tungsten with reaction equations. For example, the formula WO ₃ + 3H ₂ = W + 3H ₂ O. In it, the metal of tungsten is reduced from the oxide, its property of interaction with hydrogen is manifested. This equation reflects the process of obtaining tungsten from its trioxide. The following formula denotes a property such as the practical insolubility of tungsten in acids: W + 2HNO3 + 6HF = WF6 + 2NO + 4H2O. One of the most remarkable substances containing tungsten is carbonyl. It produces dense and ultra-thin coatings of pure tungsten.

History of the discovery

Tungsten is a metal that got its name from the Latin language. In translation this word means "wolf foam". Such an unusual name appeared due to the behavior of the metal. Accompanying the extracted tin ore, tungsten prevented the release of tin. Because of it in the process of smelting only slags were formed. About this metal said that he "eats tin, like a wolf eats a sheep." For many, I wonder who discovered the chemical element of tungsten?

This scientific discovery was made simultaneously in two places by different scientists, independently of each other. In 1781 a chemist from Sweden Scheele received the so-called "heavy stone", conducting experiments with nitric acid and scheelite. In 1783, the chemist brothers from Spain, named Eluar, also announced the discovery of a new element. More precisely, they discovered tungsten oxide, dissolved in ammonia.

Alloys with other metals

At present, single-phase and multi-phase tungsten alloys are distinguished. They contain one or more extraneous elements. The most famous compound is an alloy of tungsten and molybdenum. The addition of molybdenum gives tungsten strength when stretched. Also to the category of single-phase alloys belong tungsten compounds with titanium, hafnium, zirconium. The greatest plasticity of tungsten is given by rhenium. However, practically using such an alloy is a rather laborious process, since rhenium is very difficult to extract.

Since tungsten is one of the most refractory materials, it is not an easy task to obtain tungsten alloys. When this metal just begins to boil, the others are already passing into the liquid or the state of the gas. But modern scientists know how to make alloys using the electrolysis process. Alloys containing tungsten, nickel and cobalt are used to apply a protective layer to unstable materials.

In the modern metallurgical industry, alloys are also produced using a tungsten powder. To create it, special conditions are necessary, including the creation of a vacuum environment. Because of certain features of the interaction of tungsten with other elements, metallurgists prefer to create alloys not of two-phase characteristics, but with the use of 3, 4 or more components. These alloys are particularly strong, but with strict observance of the formulas. At the slightest deviation of the percentage components, the alloy can be brittle and unfit for use.

Tungsten is an element used in engineering

From this metal filaments are made of ordinary light bulbs. As well as tubes for X-ray machines, the components of vacuum furnaces, which should be used at extremely high temperatures. Steel, which includes tungsten, has a very high level of strength. Such alloys are used for the manufacture of tools in a variety of areas: for drilling wells, in medicine, and in machine building.

The main advantage of joining steel and tungsten is wear resistance, low probability of damage. The most famous in the construction of tungsten alloy is called "win". Also this element is widely used in the chemical industry. With its addition create paints, pigments. Tungsten oxide 6 was especially widely used in this field. It is used for the production of tungsten carbides and halides. Another name for this substance is tungsten trioxide. Tungsten oxide 6 is used as a yellow pigment in paints for ceramics and glass products.

What are heavy alloys?

All alloys based on tungsten, which have a high density, are called heavy. They are obtained only by the methods of powder metallurgy. Tungsten is always the basis of heavy alloys, where its content can be up to 98%. In addition to this metal, nickel, copper and iron are added to heavy alloys. However, they can include chrome, silver, cobalt, molybdenum. The most popular were alloys of VMZ (tungsten-nickel-iron) and VNM (tungsten-nickel-copper). A high level of density of such alloys allows them to absorb dangerous gamma radiation. Of these, wheel flywheels, electrical contacts, rotors for gyroscopes are manufactured.

Wolfram carbide

About half of all tungsten is used to make strong metals, especially tungsten carbide, which has a melting point of 2770 ° C. Tungsten carbide is a chemical compound containing an equal number of carbon atoms and tungsten. This alloy has special chemical properties. Tungsten gives it such strength that it outperforms steel by this factor twice.

Tungsten carbide is widely used in industry. It produces cutting objects, which must be very resistant to high temperatures and abrasion. Also from this element are manufactured:

• Details of aircraft, engines of cars.
• Details for spaceships.
• Medical surgical instruments that are used in the field of cavitary surgery. Such tools are more expensive than conventional medical steel, but they are more productive.
• Jewelry, especially engagement rings. Such a popularity of tungsten is associated with its strength, which for the wedding symbolizes the strength of the relationship, as well as the appearance. The characteristics of tungsten in polished form are such that it retains a mirror, brilliant appearance for a very long time.
• Balls for ballpoint pens luxury.

Win - tungsten alloy

In the second half of the 1920s, alloys began to be produced in many countries for cutting tools that were made from tungsten carbides and metallic cobalt. In Germany, such an alloy was called vidia, in the States - carbol. In the Soviet Union such an alloy was called "win". These alloys were excellent for the processing of cast iron products. The winner is a metal-ceramic alloy with an extremely high level of strength. It is made in the form of plates of various shapes and sizes.

The manufacturing process is won by the following: take a powder of tungsten carbide, a fine powder of nickel or cobalt, and everything is mixed and pressed into special shapes. The plates so compressed are subjected to further temperature treatment. This gives a very hard alloy. These plates are used not only for cutting cast iron, but also for the manufacture of drilling tools. Plates from the won are welded to the drilling equipment with copper.

Prevalence of tungsten in nature

This metal is very rare in the environment. After all the elements, it occupies the 57th place and is contained in the form of tungsten clark. Also, the metal forms minerals - scheelite and wolframite. Tungsten migrates into the groundwater either in the form of its own ion, or in the form of all kinds of compounds. But its greatest concentration in groundwater is negligible. It amounts to hundredths of a mg / l and practically does not change their chemical properties. Tungsten can also enter natural reservoirs from the drains of factories and factories.

Influence on the human body

Tungsten practically does not enter the body with water or food. There may be a danger of inhaling tungsten particles together with air in the workplace. However, despite belonging to the category of heavy metals, tungsten is not toxic. Tungsten poisoning occurs only in those who are associated with tungsten production. In this case, the degree of influence of metal on the body is different. For example, tungsten powder, tungsten carbide and a substance such as tungstic acid anhydrite can cause lung damage. Its main symptoms are general malaise, fever. The stronger symptoms occur when tungsten alloys are poisoned. This occurs when inhaling dust of alloys and leads to bronchitis, pneumosclerosis.

Metallic tungsten, getting inside the human body, is not absorbed in the intestine and is gradually eliminated. Tungsten compounds related to soluble compounds may be of great danger. They are deposited in the spleen, bones and skin. With prolonged exposure to tungsten compounds, symptoms such as brittle nails, peeling of the skin, various kinds of dermatitis can occur.

Tungsten reserves in various countries

The largest resources of tungsten are in Russia, Canada and China. According to the scientists' forecasts, about 943 thousand tons of this metal are located on the domestic territories. If you believe these estimates, the vast majority of the reserves are located in South Siberia and the Far East. Very little is the share of proven resources - it is only about 7%.

According to the number of explored deposits of tungsten, Russia is second only to China. Most of them are located in the regions of Kabardino-Balkaria and Buryatia. But in these deposits not pure tungsten is produced, but its ores containing also molybdenum, gold, bismuth, tellurium, scandium and other substances. Two-thirds of the obtained volumes of tungsten from the reconnoitered sources are enclosed in difficult-enriching ores, where the main tungsten-containing mineral is scheelite. The share of light-enriching ores accounts for only a third of the total production. The characteristics of tungsten produced in Russia are lower than in other countries. The ores contain a large percentage of tungsten trioxide. In Russia, there are very few placer deposits of metal. Tungsten sands are also of low quality, with a large number of oxides.

Tungsten in the economy

Global production of tungsten began its growth approximately from 2009, when the Asian industry began to recover. The largest producer of tungsten remains China. For example, in 2013, the share of production of this country accounted for 81% of the world supply. About 12% of the demand for tungsten is associated with the production of lighting equipment. According to experts, the use of tungsten in this area will be reduced against the background of the use of LED and fluorescent lamps both in domestic conditions and in production.

It is believed that there will be a growing demand for tungsten in the production of electronic equipment. High wear resistance of tungsten and its ability to withstand electricity make this metal the most suitable for the production of voltage regulators. However, in terms of volume, this demand remains rather insignificant, and it is estimated that by 2018 it will grow by only 2%. However, according to the forecasts of scientists, in the near future there should be an increase in demand for cemented carbide. This is due to the growth of automotive production in the US, China, Europe, as well as an increase in the mining industry. It is believed that by 2018 the demand for tungsten will increase by 3.6%.