Density of tungsten. Properties and Applications of Tungsten

Diagram of world production of tungsten (in thousand tons) in the first half of the 20th century.
Tungsten steel and other alloys containing tungsten or its carbides are used to make tank armor, torpedo and projectile shells, and the most important parts of aircraft and engines.

Tungsten is an indispensable component of the best grades of tool steel. In general, metallurgy absorbs almost 95% of all mined tungsten. (It is characteristic that it widely uses not only pure tungsten, but mainly cheaper ferrotungsten - an alloy containing 80% W and about 20% Fe; it is obtained in electric arc furnaces).

Tungsten alloys have many remarkable qualities. The so-called heavy metal (from tungsten, nickel and copper) is used to make containers in which radioactive substances are stored. Its protective effect is 40% higher than that of lead. This alloy is also used in radiotherapy, as it creates sufficient protection with a relatively small thickness of the screen.

An alloy of tungsten carbide with 16% cobalt is so hard that it can partially replace diamond when drilling wells.

Pseudo-alloys of tungsten with copper and silver are an excellent material for switches and switches for high voltage electric current: they last six times longer than conventional copper contacts.

The use of tungsten in the hairs of electric lamps was discussed at the beginning of the article. The indispensability of tungsten in this area is explained not only by its refractoriness, but also by its ductility. From one kilogram of tungsten, a wire 3.5 km long is drawn, i.e. this kilogram is enough to make filaments for 23,000 60-watt light bulbs. It is due to this property that the global electrical industry consumes only about 100 tons of tungsten per year.

In recent years, the chemical compounds of tungsten have acquired great practical importance. In particular, phosphotungstic heteropolyacid is used for the production of varnishes and bright, light-resistant paints. A solution of sodium tungstate Na2WO4 gives fabrics fire resistance and water resistance, and tungstates of alkaline earth metals, cadmium and rare earth elements are used in the manufacture of lasers and luminous paints.

The past and present of tungsten give every reason to consider it a hard-working metal.

Properties of tungsten

Tungsten- it's metal. It is not in the water of the seas, it is not in the air, and in the earth's crust it is only 0.0055%. Such tungsten, element, standing at the 74th position in . For industry, it was "opened" 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 through any material. remained "invincible" even at temperatures of thousands of degrees, therefore it was called red-resistant. Manufacturers from different countries who visited the exhibition took the development into service. The production of alloyed steel has acquired a global scale.

Interestingly, the element itself was discovered back in the 18th century. In 1781, the Swede Scheeler experimented with the mineral tungsten. The chemist decided to put it in nitric acid. In the decomposition products, the scientist discovered an unknown gray metal with a silvery sheen. The mineral on which the 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, and therefore a worthy application for the metal was found much later. The name was chosen immediately. Word tungsten existed before. The Spaniards called this one of the minerals found in the deposits of the country.

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

The melting point of the metal competes with hydrogen, and it is the most temperature-resistant element. Therefore, and install softening index of tungsten could not for a hundred years. There were no furnaces capable of heating up to several thousand degrees.

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

Tungsten mining

Most often, trioxide 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 just to hydrogen. In it tungsten is melted down at three thousand degrees Celsius.

The alloy goes to cutters, pipe cutters, cutters. for metal processing with application of tungsten improve the accuracy of parts manufacturing. When exposed to metal surfaces, friction is high, which means that the working surfaces are very hot. Cutting and polishing machines without element No. 74 can melt themselves. This makes the cut inaccurate, imperfect.

Tungsten is not only difficult to melt, but also to process. In the hardness scale, the metal occupies the ninth position. Corundum has the same number of points, from the crumbs of which, for example, a knife is made. Only diamond is harder. Therefore, with its help, tungsten is processed.

Application of tungsten

The "steadfastness" of the 74th element attracts. Products made of alloys with gray-silver metal cannot be scratched, bent, broken, unless, of course, they are scraped over the surface or with the same diamonds.

Tungsten jewelry has another indisputable plus. 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 combination with carbon.

It is recognized as the hardest alloy in the history of mankind. Its polished surface perfectly reflects light. Jewelers call it the "gray mirror".

By the way, jewelry craftsmen turned their attention to tungsten after the cores of bullets, shells and plates for bulletproof vests began to be made from this substance in the middle of the 20th century.

Customers' complaints about the fragility of the highest standards and silver jewelry made jewelers think about a 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.

Being a precious metal tungsten worth a lot of money. For a kilogram they ask for at least 50 dollars in the wholesale market. The world industry consumes 30 thousand tons of element No. 74 per year. More than 90% is absorbed by the metallurgical industry.

Only made from tungsten containers for storage of nuclear waste. Metal does not transmit destructive rays. A rare element is added to alloys for the manufacture of 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, do not fade from the sun's rays.

BUT sodium tungstate solution resistant to moisture and fire. It becomes clear what impregnated waterproof and fireproof fabrics for suits of divers and firefighters.

Tungsten deposits

There are several deposits of tungsten 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.

There is even a legend in the Celestial Empire 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 liked 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 did not find, but found tungsten.

Tungsten. Chemical element, symbol W (Latin Wolframium, English Tungsten, French Tungstene, German Wolfram, from German Wolf Rahm - wolf saliva, foam). Has a serial number 74, atomic weight 183.85, density 19.30 g/cm3, melting point 3380° C, boiling point 5680°C.

Tungsten is a light gray metal, at room temperature it has high corrosion resistance in water and in air, as well as in acids and alkalis. It begins to oxidize slightly in air at 400-500° C (at a temperature of red heat) and intensively oxidized at higher temperatures. Tungsten forms two stable oxides: WO3 and WO2 . Tungsten does not interact with hydrogen practically until the melting itself, and it begins to react with nitrogen only at temperatures above 2000° C. With chlorine, tungsten forms chlorides WCl 2 , WCl 4 , WCl 5 , WCl 6 . Solid carbon and some gases containing it 1100-1200° C react with tungsten to form carbides WC and W2C.

Tungsten dissolves in mixtures of hydrofluoric and nitric acid , also dissolves in molten alkalis with access to air and especially oxidizing agents. Separate acids do not act on tungsten.

Very high purity tungsten is ductile at room temperature. In terms of strength at high temperatures, tungsten surpasses all other metals. On themechanical properties tungsten is strongly influenced by impurities. The content of small amounts of impurities in the metal makes it very brittle (cold brittle). Oxygen, nitrogen, carbon, iron, phosphorus, and silicon have the most negative effect on the properties of tungsten.

Tungsten is widely used in the radio-tube, radio engineering and electronic-vacuum industries for the manufacture of incandescent filaments, heaters and screens for high-temperature vacuum furnaces, electrical contacts, and X-ray tube cathodes.

In metallurgy, steels are alloyed with tungsten and used in the manufacture of hard alloys (for example, a cermet alloy based on tungsten carbide will win), in the chemical industry, paints and catalysts are made from it, in rocket technology - products operating at very high temperatures, in the nuclear industry - crucibles for storing radioactive materials, as protective effect of tungsten alloy, nickel and copper is higher than that of lead . Alloys with metals are obtained by sintering, and not by pressure, because at the melting point of tungsten, many metals turn into steam.

Tungsten is also used for coating: on parts operating at very high temperatures in reducing and neutral media; for casting molds molybdenum used to produce rods of highly radioactive metals; on friction parts.

Alloys based on tungsten with rhenium are also common. Rhenium additive (up to 20-25%) reduces the transition temperature of tungsten to a brittle state, sharply increases its ductility at normal temperature and improves technological properties. Alloys are obtained by powder metallurgy and melting in electric arc vacuum furnaces. Thermocouples and electrical contacts are made from these alloys.

Tungsten alloys with molybdenum suitable for operation at temperatures above 3000° C, they are used for jet engine nozzles.

When tungsten is heated above 400° C, a powdery yellow oxide is formed on its surface, which evaporates noticeably at temperatures above 800° C. Therefore, tungsten can be used as a high-strength material at high temperatures only if the surface of the product is reliably protected from the effects of an oxidizing environment or when working in a neutral environment or in a vacuum. For short-term protection of tungsten from oxidation at 2000-3000° With use of ceramic enamel-like coatings containing refractory compounds as the main filler they are refractory binder glass.

Tungsten did not find practical application for a long time. And only at the end of the 19th century, the remarkable properties of this metal began to be used in industry. Currently, about 80 percent of mined tungsten is used in tungsten steels, about 15 percent of tungsten is used for the production of hard alloys. An important area of ​​application of pure tungsten and pure alloys from it is the electrical industry, where it is used in the manufacture of filaments of electric lamps, for parts of radio lamps and X-ray tubes, automotive and tractor electrical equipment, electrodes for contact, atomic hydrogen and argon arc welding, heaters for electric furnaces, etc. Tungsten compounds have found application in the production of fire-resistant, water-resistant and weighted fabrics, as catalysts in the chemical industry.
The value of tungsten is especially enhanced by its ability to form alloys with various metals - iron, nickel, chromium, cobalt, molybdenum, which are included in steel in various quantities. Tungsten, added in small quantities to steel, reacts with the harmful impurities of sulfur, phosphorus, arsenic contained in it and neutralizes their negative effect. As a result, steel with the addition of tungsten receives high hardness, refractoriness, elasticity and acid resistance. Everyone knows the high quality of blades made of Damascus steel, which contains a few percent of tungsten impurities. Also in. In 1882, tungsten began to be used in the manufacture of bullets. Gun steel, armor-piercing shells also contain tungsten. Steel with a tungsten additive is used to manufacture durable springs for automobiles and railway cars, springs and critical parts of various mechanisms. Rails made of tungsten steel withstand much higher loads and have a much longer service life than rails made from conventional steels. A remarkable property of steel with the addition of 918 percent tungsten is its ability to self-harden, that is, with increasing loads and temperatures, this steel becomes even stronger. This property was the basis for the manufacture of a whole series of tools from the so-called "high-speed tool steel". The use of cutters from it made it possible at one time to increase the speed of processing parts on metal-cutting machines several times.
And yet tools made of high speed steel are 35 times slower than hard alloy tools. These include compounds of tungsten with carbon (carbides) and boron (borides). These alloys are close to diamonds in hardness. If the conditional hardness of the hardest of all diamond substances is expressed by 10 points, then the hardness of tungsten carbide (vocar) is 9.8. Among these alloys is the widely known alloy of carbon with tungsten and the addition of cobalt. Pobedit itself has fallen into disuse, but this name has been preserved in relation to a whole group of hard alloys. In the engineering industry, dies for forging presses are also made from hard alloys. They wear out about a thousand times slower than steel.
A particularly important and interesting area of ​​application of tungsten is the manufacture of filaments (filaments) of electric incandescent lamps. Pure tungsten is used to make light bulb filaments. The light emitted by a hot tungsten filament is close to daylight. And the amount of light emitted by a lamp with a tungsten filament is several times higher than the radiation of lamps from filaments made from other metals (octium, tantalum). Light emission (luminous efficiency) of electric lamps with a tungsten filament is 10 times higher than that of previously used carbon filament lamps. The brightness of the glow, durability, efficiency in the consumption of electricity, low metal costs and ease of manufacture of electric lamps with a tungsten filament provided them with the widest application in lighting.
The wide possibilities of using tungsten were discovered as a result of the discovery made by the famous American physicist Robert Williams Wood. In one of the experiments, R. Wood drew attention to the fact that the glow of a tungsten filament from the end part of the cathode tube of its design continues even after the electrodes are disconnected from the battery. This impressed his contemporaries so much that R. Wood began to be called a sorcerer. Studies have shown that around a heated tungsten filament, thermal dissociation of hydrogen molecules occurs; they break up into individual atoms. After the energy is turned off, the hydrogen atoms recombine into molecules, and in doing so, a large amount of thermal energy is released, sufficient to heat a thin tungsten filament and cause it to glow. Based on this effect, a new type of metal welding, atomic hydrogen, was developed, which made it possible to weld various steels, aluminum, copper, brass in thin sheets with a clean and even weld. Metallic tungsten is used as electrodes. Tungsten electrodes are also used in the more widespread argon arc welding.
In the chemical industry, tungsten wire, which is highly resistant to acids and alkalis, is used to make various filter screens. Tungsten has found application also as a catalyst with its help to change the rate of chemical reactions in the technological process. A group of tungsten compounds is used in industry and laboratory conditions as reagents for the determination of protein and other organic and inorganic compounds.
Tungsten compounds are also used in the printing industry as paints (saffron, tungsten blue, tungsten yellow). Pyrotechnicians add tungsten compounds to combustible mixtures and get multi-colored fires of rockets and fireworks. Light printing uses paper treated with sodium wolframite. In the textile industry, a salt of tungstic acid with sodium tungstate is used to etch fabrics during dyeing. Such fabrics are waterproof and are not afraid of fire. Wood also becomes fire resistant if it is treated with this substance.

Tungsten ditelluride WTe 2 is used to convert thermal energy into electrical energy (thermo-EMF about 57 μV/K).

The coefficient of thermal expansion of tungsten is close to that of silicon, therefore, silicon crystals of powerful transistors are soldered onto tungsten substrates in order to avoid cracking of these crystals when heated.
Even an incomplete list of the use of tungsten and its compounds in industry gives an idea of ​​the high value of this element. Now it is difficult to imagine how any of us could manage even in everyday life without tungsten. And of course, the possibilities of its use will continue to be revealed.
Almost the entire world tungsten industry during the First World War was concentrated in Germany. But the raw materials for it, tungsten concentrates, were supplied from other countries. Therefore, isolated from suppliers of raw materials, the Germans were forced to process the slag accumulated near the tin smelters (remember the "wolf foam"!) And receive from them about 100 tons of tungsten per year.
At the same time, the needs of the military industry for tungsten caused a "tungsten fever" in many countries. In Russia, the Urals and Transbaikalia became suppliers of tungsten ores. Trying to cash in on the "tungsten fever", entrepreneurs did not really consider the interests of the state. So, the industrialist Tolmachev, who owned the Trans-Baikal deposits of Bukuka and Olandu, decided to lease them to a Swedish company. And only the timely intervention of the Geological Committee prevented this. In wartime conditions, the mines from this businessman were requisitioned.

The artificial radionuclide 185 W is used as a radioactive label in the study of matter. Stable 184 W is used as a component of uranium-235 alloys used in solid-phase nuclear rocket engines, since it is the only common tungsten isotope that has a low thermal neutron capture cross section (about 2 barns).

Before the outbreak of World War I in 1913, 8,123 tons of tungsten concentrate (containing 60 percent tungsten trioxide) were produced worldwide. Before the Second World War, its production increased rapidly and in 1940 amounted to 44,013 tons (excluding the Soviet Union). According to the US Bureau of Mines, in 1972, world production of tungsten was about 38,400 tons.

Tungsten alloys have many remarkable qualities. The so-called heavy metal (from tungsten, nickel and copper) is used to make containers in which radioactive substances are stored. Its protective effect is 40% higher than that of lead. This alloy is also used in radiotherapy, as it creates sufficient protection with a relatively small thickness of the screen.

An alloy of tungsten carbide with 16% cobalt is so hard that it can partially replace diamond when drilling wells.

Pseudo-alloys of tungsten with copper and silver are an excellent material for knife switches and high voltage switches: they last six times longer than conventional copper contacts.

The use of tungsten in the hairs of electric lamps was discussed at the beginning of the article. The indispensability of tungsten in this area is explained not only by its refractoriness, but also by its ductility. From one kilogram of tungsten, a wire 3.5 km long is drawn, i.e. this kilogram is enough to make filaments for 23,000 60-watt light bulbs. It is due to this property that the global electrical industry consumes only about 100 tons of tungsten per year.

In recent years, the chemical compounds of tungsten have acquired great practical importance. In particular, phosphotungstic heteropolyacid is used for the production of varnishes and bright, light-resistant paints. A solution of sodium tungstate Na 2 WO 4 gives fabrics fire resistance and water resistance, and tungstates of alkaline earth metals, cadmium and rare earth elements are used in the manufacture of lasers and luminous paints.

Back in the 16th century, the mineral wolframite was known, which, translated from German ( Wolf Rahm) means "wolf cream". The mineral received this name in connection with its features. The fact is that tungsten, which accompanied tin ores, during the smelting of tin simply turned it into foam of slag, which is why they said: "devours tin like a wolf a sheep." After a while, it was from wolframite that the name tungsten was inherited by the 74th chemical element of the periodic system.

Characteristics of tungsten

Tungsten is a light gray transition metal. It has an external resemblance to steel. Due to the possession of rather unique properties, this element is a very valuable and rare material, the pure form of which is not found in nature. Wolfram has:

• a sufficiently high density, which equates to 19.3 g / cm 3;
• high melting point, component 3422 0 С;
• sufficient electrical resistance - 5.5 μOhm * cm;
• a normal linear expansion parameter coefficient equal to 4.32;
• the highest boiling point among all metals, equal to 5555 0 С;
• low evaporation rate, even despite temperatures exceeding 200 0 С;
• relatively low electrical conductivity. However, this does not prevent tungsten from being a good conductor.

All this makes tungsten a very durable metal that is not susceptible to mechanical damage. But the presence of such unique properties does not exclude the presence of disadvantages that tungsten also has. These include:

• high fragility when exposed to very low temperatures;
• high density, which complicates the process of its processing;
• low resistance to acids at low temperatures.

Obtaining tungsten

Tungsten, along with molybdenum, rubidium and a number of other substances, is included in the group of rare metals, which are characterized by a very small distribution in nature. In this regard, it cannot be mined in the traditional way, like many minerals. Thus, the industrial production of tungsten consists of the following steps:

• extraction of ore, which contains a certain proportion of tungsten;
• organization of proper conditions in which metal can be separated from the processed mass;
• concentration of a substance in the form of a solution or precipitate;
• purification of the chemical compound resulting from the previous step;
• isolation of pure tungsten.

Thus, a pure substance from mined ore containing tungsten can be isolated in several ways.

1. As a result of enrichment of tungsten ore by gravity, flotation, magnetic or electrical separation. In the process, a tungsten concentrate is formed, 55-65% consisting of tungsten anhydride (trioxide) WO 3 . In the concentrates of this metal, the content of impurities is monitored, which can be phosphorus, sulfur, arsenic, tin, copper, antimony and bismuth.
2. As is known, tungsten trioxide WO 3 is the main material for separating tungsten metal or tungsten carbide. Obtaining WO 3-- occurs as a result of decomposition of concentrates, leaching of an alloy or sinter, etc. In this case, a material consisting of 99.9% of WO 3 is formed at the output.
3. From tungsten anhydride WO 3 . It is by reducing this substance with hydrogen or carbon that tungsten powder is obtained. Applications of the second component for the reduction reaction are used less frequently. This is due to the saturation of WO 3 with carbides during the reaction, as a result of which the metal loses its strength and becomes more difficult to process. Tungsten powder is obtained by special methods, thanks to which it becomes possible to control its chemical composition, grain size and shape, as well as particle size distribution. Thus, the particle fraction of the powder can be increased by a rapid increase in temperature or a low hydrogen supply rate.
4. Production of compact tungsten, which has the form of rods or ingots and is a blank for further production of semi-finished products - wire, rods, strips, etc.

The latter method, in turn, includes two possible options. One of them is related to powder metallurgy methods, and the other is related to melting in electric arc furnaces with a consumable electrode.

Powder metallurgy method

Due to the fact that thanks to this method it is possible to more evenly distribute the additives that give tungsten its special properties, it is more popular.

It includes several stages:

1. The metal powder is pressed into rods;
2. The blanks are sintered at low temperatures (so-called pre-sintering);
3. Welding workpieces;
4. Obtaining semi-finished products by processing blanks. The implementation of this stage is carried out by forging or machining (grinding, polishing). It should be noted that mechanical processing of tungsten becomes possible only under the influence of high temperatures, otherwise it cannot be processed.

At the same time, the powder must be well purified with the maximum allowable percentage of impurities up to 0.05%.

This method makes it possible to obtain tungsten rods having a square section from 8x8 to 40x40 mm and a length of 280-650 mm. It should be noted that at room temperatures they are quite strong, but they have increased fragility.

Fuse

This method is used if it is necessary to obtain tungsten blanks of sufficiently large dimensions - from 200 kg to 3000 kg. Such blanks, as a rule, are necessary for rolling, pipe drawing, and the manufacture of products by casting. For melting, it is necessary to create special conditions - a vacuum or a rarefied atmosphere of hydrogen. At the output, tungsten ingots are formed, which have a coarse-grained structure, as well as high brittleness due to the presence of a large amount of impurities. The content of impurities can be reduced by premelting the tungsten in an electron beam furnace. However, the structure remains unchanged. In this connection, in order to reduce the grain size, the ingots are further melted, but already in an electric arc furnace. At the same time, alloying substances are added to the ingots during the melting process, endowing tungsten with special properties.

To obtain tungsten ingots having a fine-grained structure, arc skull melting is used with metal pouring into a mold.

The method of obtaining a metal determines the presence of additives and impurities in it. Thus, several grades of tungsten are produced today.

Tungsten grades

1. HF - pure tungsten, in which there are no additives;
2. VA - a metal containing aluminum and silicon alkali additives, which give it additional properties;
3. VM - a metal containing thorium and silicon-alkali additives;
4. VT - tungsten, which contains thorium oxide as an additive, which significantly increases the emission properties of the metal;
5. VI - metal containing yttrium oxide;
6. VL - tungsten with lanthanum oxide, which also increases the emission properties;
7. VR - an alloy of rhenium and tungsten;
8. BPH - there are no additives in the metal, however, impurities in large volumes may be present;
9. MW is an alloy of tungsten with molybdenum, which significantly increases the strength after annealing, while maintaining ductility.

Where is tungsten used?

Due to its unique properties, element 74 has become indispensable in many industries.

1. The main application of tungsten is as a basis for the production of refractory materials in metallurgy.
2. With the obligatory participation of tungsten, incandescent filaments are produced, which are the main element of lighting devices, kinescopes, as well as other vacuum tubes.
3. Also, this metal is the basis for the production of heavy alloys used as counterweights, armor-piercing cores of sub-caliber and arrow-shaped feathered artillery shells.
4. Tungsten is an electrode in argon-arc welding;
5. Its alloys are highly resistant to various temperatures, acidic environments, as well as hardness and abrasion resistance, and therefore are used in the manufacture of surgical instruments, tank armor, torpedo and projectile shells, aircraft and engine parts, as well as containers for storing nuclear weapons. waste;
6. Vacuum resistance furnaces, in which the temperature reaches extremely high values, are equipped with heating elements also made of tungsten;
7. The use of tungsten is popular for providing protection against ionizing radiation.
8. Tungsten compounds are used as alloying elements, high-temperature lubricants, catalysts, pigments, and also for converting thermal energy into electrical energy (tungsten ditelluride).