What is tungsten? What kind of material is this? Chemical properties of tungsten. Characteristics and Applications of Tungsten

Tungsten is considered the most refractory of the known metals. It was first obtained in the 18th century, but industrial use began much later, with the development of production technology.

Main Features

As the most refractory metal, tungsten has specific properties:

• The melting point of tungsten approximately corresponds to the temperature of the solar corona - 3422 ° C.
• At the same time, the density of pure tungsten puts it on par with the densest metals. Its density is almost equal to that of gold - 19.25 g/cm 3 .
• The thermal conductivity of tungsten depends on temperature and ranges from 0.31 cal/cm·sec·°С at 20°С to 0.26 cal/cm·sec·°С at 1300°С.
• The heat capacity is also close to gold and amounts to 0.15·10 3 J/(kg·K).

The metal has a body-centered cubic crystal lattice. Despite its high hardness, tungsten in a heated state is very ductile and malleable, which makes it possible to make thin wire from it, which has wide applications.

It has a silver-gray color that does not change in the open air, since tungsten has high chemical resistance, and it reacts with oxygen only at temperatures above red heat.

The chemical properties of an element usually begin to appear when heated above several hundred degrees. Under normal conditions, it does not react with most known acids, except for a mixture of hydrofluoric and nitric acids.
In the presence of certain oxidizing agents, it can react with alkali melts. In this case, to start the reaction, heating to a temperature of 400 - 500 ° C is required, and then the reaction proceeds violently, with the release of heat.

Some compounds, especially tungsten carbide, have very high hardness and are used in metallurgical production for processing hard alloys.

The given characteristics of tungsten determine the specific areas of application of the metal, both in its pure form and as part of various alloys and chemical compounds.
Tungsten is included in many heat-resistant alloys as an alloying additive to increase hardness, melting point and corrosion resistance.
The similarity of the density and heat capacity of tungsten and gold can theoretically serve to counterfeit gold bars, but this can easily be detected by measuring electrical resistance and by remelting the gold bar.

Production of tungsten

The metal does not occur in nature in its pure, native form. Most deposits are formed by oxides. The content of compounds in terms of pure metal in the ore deposit is 0.2 - 2%.
Chemical resistance and high melting point allow the production of tungsten from ore only when using specific techniques.

Most methods for the industrial production of tungsten are based on the recovery of the metal from its oxide. The first stage of production consists of beneficiation of tungsten-containing ore. Leaching and reduction operations then produce the oxide WO 3 , which is reduced to pure metal under a hydrogen atmosphere. The process temperature is about 700 °C.

As a result of the reaction, a fine metal powder is obtained. The high melting point does not allow the metal to be formed into ingots, so tungsten powder is first pressed under high pressure and then sintered in a hydrogen environment using heating to a temperature of 1300 °C. A powerful electric current is passed through the resulting bars. As a result of the high transition resistance between the metal grains, the workpiece is heated and melted.

The resulting ingot is purified by the method of zone melting, similar to the technology for producing ultra-pure semiconductors. The production of tungsten using this technology makes it possible to obtain metal of a high degree of purity without additional cleaning operations.

In the production of alloys, all components are added before the powder pressing stage, since this is no longer possible to do later. During the process of pressing, sintering and further processing of the workpiece (pressing, rolling), a uniform distribution of impurities in the alloy is ensured.

Tungsten is processed at temperatures of about one and a half thousand degrees. With this heating, the metal becomes very plastic and allows forging and stamping. Thin wire for spirals of incandescent lamps is made by drawing. In this case, metal crystals are located along the wire, increasing its strength. Since high homogeneity requirements are imposed on lamp spirals, the tungsten wire is additionally subjected to electrochemical polishing operations.

Applications of tungsten

Most applications of tungsten take advantage of its high melting point, density and ductility. Tungsten is indispensable in the following areas:

• Pure tungsten is the only metal that is used in incandescent filaments of lighting lamps, radio tubes, picture tubes and other electric vacuum devices;
• In its pure form and as part of alloys, it is used in the production of cores for sub-caliber armor-piercing projectiles and bullets;
• The high density of tungsten makes it possible to manufacture rotors for small-sized gyroscopes in rocketry and spacecraft;
• Production of non-consumable electrodes for argon-arc welding;
• Tungsten radiation protection devices are more effective than traditional lead ones. The use of tungsten is economical, despite its higher cost than lead. This is due to the fact that tungsten consumption, while the technical characteristics of the product are identical, is much less.
• Tungsten products do not require corrosion protection due to their low chemical reactivity under normal temperature conditions.

Compounds of tungsten with carbon are better known as "wins". Their high hardness is used in cutting brazing of metalworking tools - cutters, drills, milling cutters. Tools with pobedite tips are used to process almost any material, from wood, where they require almost no periodic sharpening, to any type of stone. To sharpen pobedite tools, abrasives with the highest hardness are required. Diamond and CBN abrasives, which have the highest hardness among all known, fully correspond to this.

Pobedite soldering tips are attached to the working edges of the tool using copper soldering. Borax is used as a flux.

Tungsten carbide is used in jewelry, particularly rings. The high hardness of the material allows you to maintain the shine of the product throughout its entire service life.

Pobedit is made using the powder method, using cobalt for bonding with a tungsten carbide crystal.

Tungsten based alloys

Tungsten alloys can be produced exclusively by powder metallurgy. This is caused by the large difference in melting temperatures of the metals included in the alloy. The powders of the original components, after mixing, are pressed and then sintered. As a result of capillary forces, more fusible metals fill the space between the tungsten grains, forming a monolithic alloy. Solid solutions of alloy components are formed at grain boundaries.

The most widespread are alloys of tungsten with copper, iron and nickel. The most common VNZH and VNM alloys include tungsten - nickel - iron and tungsten - nickel - copper.

To achieve special characteristics, the composition may also include silver, chromium, cobalt and molybdenum.

Tungsten alloys are used for the manufacture of parts and devices in which high density with small overall dimensions is important. These are all kinds of counterweights, flywheels, weights of centrifugal regulators, cores of bullets and shells.

There are not very many brands of tungsten known. First of all, it is technically pure tungsten - HF.

Tungsten grades used in industry typically include some additives. Material doped with lanthanum is designated as VL, and with yttrium - VI. These alloying additives further improve the mechanical and technological properties of the metal.

Alloys with rhenium - VR5, VR20 - are used in the production of high-temperature thermocouples.

Doping with thorium increases the emissive properties of tungsten, which is especially important in the manufacture of cathodes for high-power vacuum tubes. This additive also improves the ability to ignite an electric arc during argon-arc welding.

Tungsten alloys with copper and silver are used to make contacts for high-current switching equipment. Copper and silver, although highly electrically conductive, do not have high mechanical strength. When passing high currents, the contact groups may melt. Contacts made of tungsten alloys are free from these disadvantages, despite their slightly higher electrical resistance.

The high density of the alloys will make it possible to use them for the manufacture of containers for storing radioactive substances and screens for protection against γ-radiation.

Properties of tungsten

Tungsten- it's metal. It is not found in sea water, not in the air, and in the earth’s crust it is only 0.0055%. That's how tungsten, element, standing in 74th position in. It was “opened” for industry by the World Exhibition in the French capital. It took place in 1900. The exhibition featured tungsten steel.

The composition was so hard that it could cut any material. remained “invincible” even at temperatures of thousands of degrees, which is why it was called red-resistant. Manufacturers from different countries who visited the exhibition adopted the development. The production of alloy steel has acquired a global scale.

Interestingly, the element itself was discovered back in the 18th century. In 1781, Swede Scheeler conducted experiments with the mineral tungsten. The chemist decided to place it in nitric acid. In the decomposition products, the scientist discovered an unknown gray metal with a silvery tint. The mineral on which experiments were carried out was later renamed scheelite, and the new element called tungsten.

However, it took a lot of time to study its properties, so worthy use of the metal was found much later. The name was chosen right away. The word tungsten existed before. The Spaniards called this one of the minerals found in the country's deposits.

The composition of the stone actually included element No. 74. Externally, the metal is porous, as if foamed. Therefore, another analogy came in handy. In German, tungsten literally means “wolf foam”.

The melting point of the metal rivals that of hydrogen, which is the most temperature-resistant element. Therefore, install tungsten softening index They couldn't for a hundred years. There were no furnaces capable of heating up to several thousand degrees.

When the “benefits” of the silver-gray element were “seen through,” they began to mine it on an industrial scale. For the 1900 exhibition, the metal was extracted the old fashioned way using nitric acid. However, tungsten is still mined this way.

Tungsten mining

Most often, the trioxide substance is first obtained from ore waste. It is processed at 700 degrees, obtaining pure metal in the form of dust. To soften the particles one has to resort to hydrogen. In it tungsten is melted down at three thousand degrees Celsius.

The alloy is used for cutters, pipe cutters, and milling cutters. for metal processing with using tungsten increase the accuracy of parts manufacturing. When exposed to metal surfaces, friction is high, which means that the working planes become very hot. Cutting and polishing machines without element No. 74 may themselves melt. This makes the cut inaccurate and imperfect.

Tungsten is not only difficult to melt, but also difficult to process. On the hardness scale, the metal occupies the ninth position. Corundum has the same number of points, the crumbs of which are used to make, for example, sandpaper. Only diamond is harder. Therefore, tungsten is processed with its help.

Applications of tungsten

The “steadfastness” of the 74th element attracts. Products made from alloys with gray-silver metal cannot be scratched, bent, or broken, unless, of course, you scratch them on the surface or with the same diamonds.

Tungsten jewelry has another undeniable advantage. They do not cause allergic reactions, unlike gold, silver, platinum and, even more so, their alloys with or. For jewelry, tungsten carbide is used, that is, its compound with carbon.

It is recognized as the hardest alloy in human history. Its polished surface perfectly reflects light. Jewelers call it “gray mirror”.

By the way, jewelry masters paid attention to tungsten after the cores of bullets, shells and plates for body armor began to be made from this substance in the mid-20th century.

Customer complaints about the fragility of high-grade silver jewelry forced jewelers to remember the new element and try to apply it in their industry. In addition, prices began to fluctuate. Tungsten has become an alternative to the yellow metal, which is no longer perceived as an investment item.

Being a precious metal, tungsten costs a lot of money. Per kilogram they ask for at least 50 dollars on the wholesale market. World industry spends 30 thousand tons of element No. 74 per year. More than 90% is absorbed by the metallurgical industry.

Only made from tungsten containers for storing nuclear waste. Metal does not transmit destructive rays. The rare element is added to alloys for making surgical instruments.

What is not used for metallurgical purposes is taken by the chemical industry. Tungsten compounds with phosphorus, for example, are the basis of varnishes and paints. They do not collapse or fade from sunlight.

A sodium tungstate solution resistant to moisture and fire. It becomes clear what waterproof and fireproof fabrics for divers’ and firefighters’ suits are impregnated with.

Tungsten deposits

There are several tungsten deposits in Russia. They are located in Altai, the Far East, the North Caucasus, Chukotka and Buryatia. Outside the country, the metal is mined in Australia, the USA, Bolivia, Portugal, South Korea and China.

In the Celestial Empire there is even a legend about a young explorer who came to China to look for a tin stone. The student settled in one of the houses in Beijing.

After a fruitless search, the guy loved to listen to the stories of the owner’s daughter. One evening she told the story of the dark stones from which the home stove was built. It turned out that the blocks were falling from the cliff into the backyard of the building. So, the student didn’t find it, but he did find tungsten.

Tungsten also belongs to the group of metals characterized by high refractoriness. It was discovered in Sweden by a chemist named Scheele. It was he who was the first to isolate the oxide of an unknown metal from the mineral wolframite in 1781. The scientist managed to obtain tungsten in its pure form after 3 years.

Description

Tungsten belongs to a group of materials that are often used in various industries. He denoted by the letter W and in the periodic table it has serial number 74. It is characterized by a light gray color. One of its characteristic qualities is high refractoriness. The melting point of tungsten is 3380 degrees Celsius. If we consider it from the point of view of application, the most important qualities of this material are:

• density;
• melting point;
• electrical resistance;
• linear expansion coefficient.

When calculating its characteristic qualities, it is necessary to highlight the high boiling point, which is located at at a level of 5,900 degrees Celsius. Another feature is its low evaporation rate. It is low even in temperature conditions of 2000 degrees Celsius. In terms of electrical conductivity, this metal is 3 times superior to such a common alloy as copper.

Factors limiting the use of tungsten

There are a number of factors that limit the use of this material:

• high density;
• significant tendency to become brittle at low temperatures;
• low oxidation resistance.

In appearance, tungsten resembles regular steel. Its main application is mainly related to the production of alloys with high strength characteristics. This metal can be processed, but only if it is preheated. Depending on the type of treatment chosen, heating is carried out to a certain temperature. For example, if the task is to forge rods from tungsten, then the workpiece must be preheated to a temperature of 1450-1500 degrees Celsius.

For 100 years, tungsten was not used for industrial purposes. Its use in the production of various equipment was limited by its high melting point.

The beginning of its industrial use dates back to 1856, when it was first used for alloying tool grades of steel. During their production, tungsten was added to the composition with a total share of up to 5%. The presence of this metal in the steel made it possible to increase the cutting speed on lathes from 5 to 8 m per minute.

The development of industry in the second half of the 19th century is characterized by the active development of the machine tool production industry. The demand for equipment was constantly increasing every year, which required machine builders to obtain high-quality characteristics of machines, and in addition to this, increase their operating speed. The first impetus for increasing cutting speed was the use of tungsten.

Already at the beginning of the 20th century, the cutting speed was increased up to 35 meters per minute. This was achieved by alloying the steel not only with tungsten, but also with other elements:

• molybdenum;
• chrome;
• vanadium

Subsequently, the cutting speed on the machines increased to 60 meters per minute. But, despite such high indicators, experts understood that there was an opportunity to improve this characteristic. Experts did not think for a long time about which method to choose to increase the cutting speed. They resorted to using tungsten, but in the form of carbides in conjunction with other metals and their types. Currently, the metal cutting speed on machine tools is 2000 meters per minute.

Like any material, tungsten has its own special properties, thanks to which it falls into the group of strategic metals. We have already said above that one of the advantages of this metal is its high refractoriness. It is thanks to this property that the material can be used to make incandescent filaments.

Its melting point is at 2500 degrees Celsius. But the positive properties of this material are not limited to this quality alone. It also has other advantages that should be mentioned. One of them is high strength, demonstrated under normal and elevated temperatures. For example, when iron and alloys made from it are heated to a temperature of 800 degrees Celsius, the strength decreases by 20 times. Under the same conditions, the strength of tungsten decreases only three times. At 1500 degrees Celsius, the strength of iron is practically reduced to zero, but for tungsten it is at the level of iron at ordinary temperatures.

Today, 80% of the world's tungsten production is used primarily in the production of high-quality steel. More than half of the steel grades used by machine-building enterprises contain tungsten. They use them as the main material for turbine parts, gearboxes, and also use such materials for the manufacture of compressor machines. Shafts, gears, and a solid forged rotor are made from engineering steels containing tungsten.

In addition, they are used for the manufacture of crankshafts and connecting rods. Adding to the composition of engineering steel, in addition to tungsten and other alloying elements, increases their hardenability. In addition, it is possible to obtain a fine-grained structure. Along with this, characteristics such as hardness and strength increase in the produced engineering steels.

In the production of heat-resistant alloys, the use of tungsten is one of the prerequisites. The need to use this particular metal is due to the fact that it is the only one that is able to withstand significant loads under conditions of high temperatures exceeding the melting value of iron. Tungsten and compounds based on this metal are highly durable and have good elasticity. In this regard, they are superior to other metals included in the group of refractory materials.

Cons

However, while listing the advantages of tungsten, one cannot fail to note disadvantages inherent in this material.

Tungsten, which is currently produced, contains 2% thorium. This alloy is called thoriated tungsten. It is characteristic of him tensile strength 70 MPa at a temperature of 2420 degrees Celsius. Although the value of this indicator is low, we note that only 5 metals, together with tungsten, do not change their solid state at this temperature.

This group includes molybdenum, which has a melting point of 2625 degrees. Another metal is technetium. However, alloys based on it are unlikely to be produced in the near future. Rhenium and tantalum do not have high strength under these temperature conditions. Therefore, tungsten is the only material that is able to provide sufficient strength at high temperature loads. Due to the fact that it is one of the scarce products, if there is an opportunity to replace it, then manufacturers use an alternative to it.

However, in the production of individual components there are no materials that could fully replace tungsten. For example, in the manufacture of incandescent filaments of electric lamps and anodes of DC arc lamps, only tungsten is used, since there are simply no suitable substitutes. It is also used in the manufacture of electrodes for argon-arc and atomic-hydrogen welding. Also, using this material, a heating element is made, used in conditions of 2000 degrees Celsius.

Application

Tungsten and alloys made on its basis are widely used in various industries. They are used in the production of aircraft engines, used in the field of rocketry, as well as for the production of space technology. In these areas, jet nozzles and critical section inserts in rocket engines are made using these alloys. In addition, such materials are used as base materials for the manufacture of rocket alloys.

The production of alloys from this metal has one feature, which is associated with the refractoriness of this material. At high temperatures, many metals change their state and turn into gases or highly volatile liquids. Therefore, to produce alloys containing tungsten, powder metallurgy methods are used.

Such methods involve pressing a mixture of metal powders, subsequent sintering and further subjecting them to arc melting, carried out in electrode furnaces. In some cases, the sintered tungsten powder is additionally impregnated with a liquid solution of some other metal. Thus, pseudo-alloys of tungsten, copper, and silver are obtained, used for contacts in electrical installations. Compared to copper ones, the durability of such products is 6-8 times higher.

This metal and its alloys have great prospects for further expansion of the scope of application. First of all, it should be noted that, unlike nickel, these materials can work at the “fiery” boundaries. The use of tungsten products instead of nickel leads to increased operating parameters of power plants. And this leads to increasing equipment efficiency. In addition, tungsten-based products can easily withstand harsh environments. Thus, we can confidently say that tungsten will continue to lead the group of such materials in the near future.

Tungsten also contributed to the process of improving the incandescent electric lamp. Before the 1898 period, these electric lighting fixtures used carbon filament.

• it was easy to make;
• its production was inexpensive.

The only disadvantage of carbon filament was that service life she had a small one. After 1898, the carbon filament of lamps had a competitor in the form of osmium. Since 1903, tantalum has been used to produce electric lamps. However, already in 1906, tungsten replaced these materials and began to be used for the manufacture of filaments for incandescent lamps. It is still used today in the manufacture of modern light bulbs.

To provide this material with high heat resistance, a layer of rhenium and thorium is applied to the metal surface. In some cases, tungsten filament is made with the addition of rhenium. This is due to the fact that at high temperatures this metal begins to evaporate, and this leads to the fact that the thread made of this material becomes thinner. Adding rhenium to the composition reduces the evaporation effect by 5 times.

Nowadays, tungsten is actively used not only in the production of electrical equipment, but also various military-industrial products. Its addition to weapon steel provides high efficiency to materials of this type. In addition, it allows you to improve the characteristics of armor protection, as well as make armor-piercing projectiles more effective.

Conclusion

Tungsten is one of the popular materials used in metallurgy. Adding it to the composition of produced steels improves their characteristics. They become more resistant to thermal loads, and in addition the melting point increases, which is especially important for products used in extreme conditions at high temperatures. The use in the production of various equipment, products and elements, assemblies made of this metal or alloys based on it makes it possible to improve the characteristics of the equipment and increase the efficiency of their operation.

Chemistry

Element No. 74 tungsten is usually classified as a rare metal: its content in the earth’s crust is estimated at 0.0055%; it is not found in seawater and could not be detected in the solar spectrum. However, in terms of popularity it can compete with many not at all rare metals, and its minerals were known long before the discovery of the element itself. So, back in the 17th century. in many European countries they knew “tungsten” and “tungsten” - this was the name then for the most common tungsten minerals - wolframite and scheelite. A elementary tungsten was discovered in the last quarter of the 18th century.

Tungsten Ore

Very soon this metal gained practical importance - as an alloying additive. And after the 1900 World Exhibition in Paris, at which samples of high-speed tungsten steel were demonstrated, element No. 74 began to be used by metallurgists in all more or less industrialized countries. The main feature of tungsten as an alloying additive is that it gives steel red resistance - it allows it to maintain hardness and strength at high temperatures. Moreover, when cooled in air (after exposure at temperatures close to red heat), most steels lose their hardness. But tungsten ones do not.
The tool, made of tungsten steel, withstands the enormous speeds of the most intense metalworking processes. The cutting speed of such a tool is measured in tens of meters per second.
Modern high-speed steels contain up to 18% tungsten (or tungsten with molybdenum), 2-7% chromium and a small amount of cobalt. They retain hardness at 700-800° C, while ordinary steel begins to soften when heated to just 200° C. “Stellites” - alloys - have even greater hardness
tungsten and with chromium and cobalt (without iron) and especially tungsten carbides - its compounds with carbon. The “visible” alloy (tungsten carbide, 5-15% cobalt and a small admixture of titanium carbide) is 1.3 times harder than ordinary tungsten steel and retains hardness up to 1000-1100 ° C. Cutters from this alloy can be cut in a minute up to 1500-2000 m of iron filings. They can quickly and accurately process “capricious” materials: bronze and porcelain, glass and ebonite; At the same time, the tool itself wears out very little.
At the beginning of the 20th century. tungsten filament began to be used in light bulbs: it allows the heat to be raised to 2200 ° C and has a high luminous efficiency. And in this capacity, tungsten is absolutely indispensable to this day. Obviously, this is why the electric light bulb is called a “tungsten eye” in one popular song.

Tungsten minerals and ores

Tungsten occurs in nature mainly in the form of oxidized complex compounds formed by tungsten trioxide WO 3 and oxides of iron and manganese or calcium, and sometimes lead, copper, thorium and rare earth elements. The most common mineral, wolframite, is a solid solution of tungstates (tungstic acid salts) of iron and manganese (mFeW0 4 *nMnW0 4). This solution is heavy and hard crystals of brown or black color, depending on which compound predominates in their composition. If there is more pobnerite (manganese compound), the crystals are black, but if iron-containing ferberite predominates, they are brown. Wolframite is paramagnetic and conducts electricity well.
Of other tungsten minerals, scheelite, calcium tungstate CaW04, is of industrial importance. It forms shiny, glass-like crystals that are light yellow, sometimes almost white. Scheelite is non-magnetic, but it has another characteristic feature - the ability to luminesce. When illuminated with ultraviolet rays, it fluoresces bright blue in the dark. The admixture of molybdenum changes the color of the glow of scheelite: it becomes pale blue, and sometimes even cream. This property of scheelite, used in geological exploration, serves as a search feature to detect mineral deposits.
Deposits of tungsten ores are theologically related to the areas of granite distribution. The largest foreign deposits of wolframite and scheelite are located in China, Burma, the USA, Bolivia and Portugal. Our country also has significant reserves of tungsten minerals, their main deposits are located in the Urals, the Caucasus and Transbaikalia.
Large crystals of wolframite or scheelite are very rare. Typically, tungsten minerals are only disseminated into ancient granite rocks - the average tungsten concentration ends up being 1-2% at best. Therefore, it is very difficult to extract tungsten from ores.

How is tungsten obtained?

The first stage is ore enrichment, separating valuable components from the main mass - waste rock. Enrichment methods are common for heavy ores and metals: grinding and flotation with subsequent operations - magnetic separation (for tungsten ores) and oxidative roasting.
The resulting concentrate is most often sintered with an excess of soda to convert tungsten into a soluble compound - sodium tungstate. Another method of obtaining this substance is leaching; tungsten is extracted with a soda solution under pressure and at elevated temperatures (the process takes place in an autoclave), followed by neutralization and precipitation in the form of artificial scheelite, i.e. calcium tungstate. The desire to obtain tungstate is explained by the fact that it is relatively simple to produce, in just two stages:
CaW0 4 → H 2 W0 4 or (NH 4) 2 W0 4 → WO 3, tungsten oxide purified from most of the impurities can be isolated.
There is another way to obtain tungsten oxide - through chlorides. Tungsten concentrate is treated with chlorine gas at elevated temperatures. The resulting tungsten chlorides are quite easily separated from the chlorides of other metals by sublimation, using the temperature difference at which these substances go into a vapor state. The resulting tungsten chlorides can be converted into oxide, or they can be processed directly into elemental metal.

Main properties

Tungsten differs from all other metals in its special heaviness, hardness and refractoriness. The expression “heavy as lead” has long been known. It would be more correct to say: “Heavy as tungsten.” The density of tungsten is almost twice that of lead, more precisely - 1.7 times. At the same time, its atomic mass is slightly lower: 184 versus 207.

Chemical activity

Natural tungsten consists of five stable isotopes with mass numbers from 180 to 186. In addition, in nuclear reactors, as a result of various nuclear reactions, another 8 radioactive isotopes of tungsten are formed with mass numbers from 176 to 188; all of them are relatively short-lived: their half-lives range from several hours to several months.
The seventy-four electrons of the tungsten atom are arranged around the nucleus in such a way that six of them are in outer orbits and can be separated relatively easily. Therefore, the maximum valence of tungsten is six. However, the structure of these outer orbits is special - they consist of two “tiers”: four electrons belong to the penultimate level -d, which is thus less than half filled. (The number of electrons in a filled d level is known to be ten.) These four electrons (obviously unpaired) can easily form a chemical bond. As for the two “outermost” electrons, it is quite easy to tear them off.
It is the structural features of the electron shell that explain the high chemical activity of tungsten. In compounds it is not only hexavalent, but also penta-, tetra-, tri-, bi- and zero-valent. (Only monovalent tungsten compounds are unknown).
The activity of tungsten is manifested in the fact that it reacts with the overwhelming majority of elements, forming many simple and complex compounds. Even in alloys, tungsten is often chemically bonded. And it interacts with oxygen and other oxidizing agents more easily than most heavy metals.
The reaction of tungsten with oxygen occurs when heated, especially easily in the presence of water vapor. If tungsten is heated in air, then at 400-500 ° C a stable lower oxide W0 2 is formed on the metal surface; the entire surface is covered with a brown film. At a higher temperature, the blue intermediate oxide W 4 O 11 is first obtained, and then lemon-yellow tungsten trioxide W0 3, which sublimes at 923 ° C.

Alloys

Tungsten forms alloys with almost all metals, but obtaining them is not so easy. The fact is that generally accepted fusion methods are, as a rule, inapplicable in this case. At the melting point of tungsten, most other metals have already turned into gases or highly volatile liquids. Therefore, alloys containing tungsten are usually produced by powder metallurgy methods.
To avoid oxidation, all operations are carried out in a vacuum or in an argon atmosphere. It's done like this. First, the mixture of metal powders is pressed, then sintered and subjected to arc melting in electric furnaces. Sometimes one tungsten powder is pressed and sintered, and the porous workpiece obtained in this way is impregnated with a liquid melt of another metal: so-called pseudo-alloys are obtained. This method is used when it is necessary to obtain an alloy of tungsten with copper and silver.

Tungsten is a dull silvery metal with the highest melting point of any pure metal.

Also known as Tungsten, from which the element takes its symbol, W, tungsten is more resistant to tearing than diamond and much harder than steel. It is the unique properties of refractory metals - its strength and ability to withstand high temperatures - that make it ideal for many commercial and industrial applications.

Tungsten is primarily extracted from two types of minerals: wolframite and scheelite. However, tungsten recycling also accounts for about 30% of global supply. China is the world's largest producer of the metal, providing more than 80% of the world's supply.

After processing and separating the tungsten ore, the chemical form, ammonium paratungstate (APT), is produced. APT can be heated with hydrogen to form tungsten oxide or reacted with carbon at temperatures above 1925 °F (1050 °C) to produce tungsten metal.

Applications:

The primary use of tungsten for over 100 years was as the filament of incandescent lamps. Made in small quantities of potassium aluminum silicate, tungsten powder is sintered at high temperatures to create the wire filament that is at the center of the light bulbs that light millions of homes around the world.

Thanks to tungsten's ability to retain its shape at high temperatures, tungsten filaments are now also used in a variety of household applications, including lamps, spotlights, heating elements in electric ovens, microwave ovens, X-ray tubes, and cathode ray tubes (CRTs) in computer monitors and televisions.

The metal's tolerance to intense heat also makes it ideal for thermocouples and electrical contacts in electric arc furnaces and welding equipment. Applications that require concentrated mass or weight, such as counterweights, fishing weights, and darts, often use tungsten due to its density.

Tungsten carbide:

Tungsten carbide is made by either combining one tungsten atom with one carbon atom (represented by the chemical symbol WC) or two tungsten atoms with one carbon atom (W2C). This is done by heating tungsten powder with carbon at temperatures ranging from 2550 °F to 2900 °F (1400 °C to 1600 °C) in a stream of hydrogen gas.

According to the Moh hardness scale (a measure of one material's ability to scratch another), tungsten carbide has a hardness of 9.5, only slightly lower than diamond. For this reason, this solid compound is sintered, a process that requires pressing and heating a powder mold at high temperatures to produce products used in machining and cutting. This results in materials that can operate under high temperature and stress conditions, such as drills, turning tools, cutters and armor-piercing ammunition.

Cemented carbide is produced using a combination of tungsten carbide and cobalt powder and is used to make wear-resistant tools such as those used in the mining industry.

The tunnel boring machine used to dig the canal tunnel linking the UK to Europe was actually fitted with almost 100 cemented carbide tips.

Tungsten alloys:

Tungsten metal can be combined with other metals to increase their strength and resistance to wear and corrosion. Steel alloys often contain tungsten for these beneficial properties. Many high-speed steels used in cutting and machining tools such as saw blades contain about 18 percent tungsten.

Tungsten steel alloys are also used in the production of rocket engine nozzles, which must have high heat-resistant properties. Other tungsten alloys include Stellite (cobalt, chromium and tungsten), which is used in bearings and pistons for its durability and wear resistance, and Hevimet, which is produced by sintering tungsten alloy powder and is used in ammunition, dart barrels, and golf clubs.

Superalloys of cobalt, iron or nickel, along with tungsten, can be used to make turbine blades for aircraft.