Tungsten metal. Tungsten: application, properties and chemical characteristics

Mother nature has enriched mankind with useful chemical elements. Some of them are hidden in its bowels and are contained in relatively small quantities, but their significance is very significant. One of these is tungsten. Its use is due to special properties.

Origin story

The 18th century - the century of the discovery of the periodic table - became fundamental in the history of this metal.

Previously, the existence of a certain substance, which is part of the mineral rocks, was accepted, which prevented the smelting of the necessary metals from them. For example, obtaining tin was difficult if the ore contained such an element. The difference in melting temperatures and chemical reactions led to the formation of slag foam, which reduced the amount of tin yield.

In the 8th century, the metal was successively discovered by the Swedish scientist Scheele and the Spaniards, the Eluard brothers. This happened as a result of chemical experiments on the oxidation of mineral rocks - scheelite and wolframite.

Registered in the periodic system of elements in accordance with atomic number 74. A rare refractory metal with an atomic mass of 183.84 is tungsten. Its use is due to unusual properties discovered already during the 20th century.

Where to looking for?

By the number in the bowels of the earth, it is "sparsely populated" and ranks 28th. It is a component of about 22 different minerals, but only 4 of them are essential for its extraction: scheelite (contains about 80% trioxide), wolframite, ferberite and hubnerite (they contain 75-77% each). The composition of the ores most often contains impurities, in some cases, a parallel "extraction" of such metals as molybdenum, tin, tantalum, etc. is carried out. The largest deposits are in China, Kazakhstan, Canada, the USA, there are also in Russia, Portugal, Uzbekistan.

How do they receive?

Due to the special properties, as well as the low content in the rocks, the technology for obtaining pure tungsten is rather complicated.

1. Magnetic separation, electrostatic separation or flotation to enrich ore to 50-60% concentration
2. Isolation of 99% oxide by chemical reactions with alkaline or acidic reagents and phased purification of the resulting precipitate.
3. Reduction of metal with carbon or hydrogen, yield of the corresponding metal powder.
4. Production of ingots or powder sintered briquettes.

One of the important stages in the production of metallurgical products is powder metallurgy. It is based on mixing powdered refractory metals, their pressing and subsequent sintering. In this way, a large number of technologically important alloys are obtained, including the use of which is found mainly in industrial production cutting tools of increased power and durability.

Physical and chemical properties

Tungsten is a refractory and heavy silver metal with a body-centered crystal lattice.

• Melting point - 3422 ˚С.
• Boiling point - 5555 ˚С.
• Density - 19.25 g / cm 3.

It is a good conductor of electricity. Doesn't magnetize. Some minerals (for example, scheelite) are luminescent.

Resistant to acids, aggressive substances at high temperatures, corrosion and aging. Tungsten also contributes to the deactivation of the influence of negative impurities in steels, the improvement of its heat resistance, corrosion resistance and reliability. The use of such iron-carbon alloys is justified by their manufacturability and wear resistance.

Mechanical and technological properties

Tungsten - hard, durable metal. Its hardness is 488 HB, tensile strength is 1130-1375 MPa. When cold, it is not plastic. At a temperature of 1600 ˚С, plasticity increases to a state of absolute susceptibility to pressure treatment: forging, rolling, drawing. It is known that 1 kg of this metal makes it possible to produce a thread with a total length of up to 3 km.

Machining is difficult due to excessive hardness and brittleness. For drilling, turning, milling, carbide tungsten-cobalt materials are used, made by powder metallurgy. Less often, at low speeds and special conditions, tools made of high-speed alloyed tungsten steel are used. Standard cutting principles are not applicable, as the equipment wears out extremely quickly, and the processed tungsten cracks. The following technologies are applied:

1. Chemical treatment and impregnation of the surface layer, including the use of silver for this purpose.
2. Surface heating with the help of furnaces, gas flame, electric current of 0.2 A. The permissible temperature at which there is a slight increase in plasticity and, accordingly, cutting improves, is 300-450 ˚С.
3. Cutting tungsten using low-melting substances.

Sharpening and grinding should be carried out with the help of diamond and less often - corundum.

Welding of this refractory metal is carried out mainly under the action of an electric arc, tungsten or carbon electrodes in an inert gas or liquid shielding. Contact welding is also possible.

This particular chemical element has characteristics that distinguish it from the mass. So, for example, being characterized by high heat resistance and wear resistance, it improves the quality and cutting properties of alloyed tungsten-containing steels, and the high melting point makes it possible to produce filaments for light bulbs and electrodes for welding.

Application

Rarity, unusualness and importance determine the widespread use in modern technology of a metal called Tungsten - tungsten. Properties and application justify the high cost and demand. High melting point, hardness, strength, heat resistance and resistance to chemical attack and corrosion, wear resistance and cutting features - these are its main trump cards. Use cases:

1. Incandescent filaments.
2. in order to obtain high-speed, wear-resistant, heat-resistant and heat-resistant iron-carbon alloys, which are used for the production of drills and other tools, punches, springs and springs, rails.
3. Manufacture of "powdered" hard alloys, mainly used as highly wear-resistant cutting, drilling or pressing tools.
4. Electrodes for argon-arc and resistance welding.
5. Manufacture of parts for X-ray and radio engineering, various technical lamps.
6. Special luminous paints.
7. Wire and parts for chemical industry.
8. Various practical small things, for example, mormyshki for fishing.

Various alloys, which include tungsten, are gaining popularity. The scope of such materials is sometimes surprising - from heavy engineering to light industry, where fabrics with special properties (for example, fire-resistant) are made.

Universal materials do not exist. Each known element and created alloys are distinguished by their uniqueness and necessity for certain areas of life and industry. However, some of them have special properties that make previously unfeasible processes possible. One such metal is tungsten. Its application is not wide enough, like steel, but each of the options is extremely useful and necessary for humanity.

Tungsten is a chemical element of the 4th group, having atomic number 74 in the periodic system of Dmitry Ivanovich Mendeleev, denoted by W (Wolframium). The metal was discovered and isolated by two Spanish chemists brothers d "Eluyar in 1783. The name "Wolframium" itself was transferred to the element from the previously known mineral wolframite, which was known back in the 16th century, it was then called "wolf foam", or "Spumalupi" in Latin, on German this phrase sounds like "WolfRahm" (Tungsten). Currently, in the USA, France, Great Britain and some other countries, the name "tungsten" (from the Swedish tungsten, which translates as "heavy stone") is used to name tungsten.

Tungsten is a gray hard transition metal. The main application of tungsten is the role of the base in refractory materials in metallurgy. Tungsten is extremely refractory, under normal conditions the metal is chemically resistant.

Tungsten differs from all other metals in its unusual hardness, heaviness and infusibility. The density of this metal is almost twice that of lead, to be precise, 1.7 times. With all this, the atomic mass of tungsten is lower and has a value of 184 versus 207 for lead.

Tungsten is a light gray metal, the melting and boiling points of this metal are the highest. Due to the plasticity and infusibility of tungsten, it is possible to use it as filaments in lighting devices, in kinescopes, and also in other vacuum tubes.

Twenty tungsten minerals are known. The most common: minerals of the wolframite scheelite group, which are of industrial importance. Less common is wolframite sulfide, i.e. tungstensite (WS2) and oxide-like compounds - ferro - and cuprotungstite, tungstite, hydrotungstite. Vads, psilomelans with a high content of tungsten, are widely distributed.

tungsten filament aircraft fuselage

Depending on the conditions of occurrence, morphology and type of tungsten deposits, open, underground, and combined methods are used in their development.

Currently, there are no methods for obtaining tungsten directly from concentrates. In this regard, intermediate compounds are first isolated from the concentrate, and then metallic tungsten is obtained from them. The isolation of tungsten includes: the decomposition of concentrates, then the transition of the metal into compounds, from which it is separated from the rest of the accompanying elements. Isolation of tungstic acid, i.e. pure chemical compound tungsten, continues with the subsequent production of tungsten in metallic form.

Tungsten is used in the manufacture of machinery and equipment for metalworking, construction and mining industry, in the manufacture of lamps and lamps, in the transport and electronic industry, in the chemical industry and other fields.

Made of tungsten steel, the tool is able to withstand the enormous speeds of the most intensive processes in metalworking. The cutting speed using such a tool is usually measured in tens of meters per second.

Tungsten is rather poorly distributed in nature. The content of metal in the earth's crust by mass is about 1.3·10?4%. The main minerals containing tungsten are natural tungstates: scheelite, originally called tungsten, and wolframite.

Tungsten production

The first stage in the production of tungsten is the enrichment of the ore, i.e. separation of valuable components from the main ore mass, waste rock. The same concentration methods are used as for other heavy metal ores: grinding and flotation, followed by magnetic separation (wolframite ores) and oxidative roasting. The concentrate obtained by this method is usually burned with an excess of soda, thereby bringing tungsten into a soluble state, i.e. to sodium wolframite.

Another method for obtaining this substance is leaching. Tungsten is extracted with a soda solution at elevated temperature and under pressure, followed by neutralization and precipitation of calcium tungstate, i.e. scheelite. Scheelite is obtained because it is quite easy to extract purified tungsten oxide from it.

CaWO 4 > H 2 WO 4 or (NH 4) 2 WO 4 > WO 3

Tungsten oxide is also obtained through chlorides. The tungsten concentrate is treated with chlorine gas at an elevated temperature. In this case, tungsten chlorides are formed, which are easily separated from other chlorides by sublimation. The resulting chloride can be used to obtain oxide or immediately extract metal from it.

In the next step, the oxides and chlorides are converted into metallic tungsten. To reduce tungsten oxide, it is best to use hydrogen. With this reduction, the metal is the purest. The reduction of the oxide takes place in a special tube furnace, where the "boat" with WO 3 moves through several temperature zones. Dry hydrogen enters towards the "boat". Oxide reduction occurs in hot (450-600°C) and cold zones (750-1100°C). In cold zones, reduction to WO 2 occurs, and then to metal. As time passes through the hot zone, the grains of powdered tungsten change their size.

Recovery can take place not only under the supply of hydrogen. Coal is often used. Due to the solid reducing agent production is simplified, but the temperature in this case should reach 1300°C. Coal itself and the impurities that it always contains, reacting with tungsten, form carbides of other compounds. As a result, the metal is contaminated. But in the electrical industry, only high-quality tungsten is used. Even 0.1% iron impurities make tungsten for the manufacture of the thinnest wire, because. it becomes much more fragile.

The isolation of tungsten from chlorides is based on pyrolysis. Tungsten and chlorine form some compounds. An excess of chlorine allows all of them to be converted into WCl6, and it, in turn, at a temperature of 1600 ° C decomposes into chlorine and tungsten. If hydrogen is present, the process starts at 1000°C.

This is how tungsten is obtained in the form of a powder, which is then pressed at high temperature in a stream of hydrogen. The first stage of pressing (heating to about 1100-1300°C) produces a brittle porous ingot. Then the pressing continues, and the temperature begins to rise almost to the melting point of tungsten. In such an environment, the metal begins to become solid and gradually acquires its qualities and properties.

On average, 30% of the tungsten produced in industry is recycled tungsten. Tungsten scrap, sawdust, shavings and powder are oxidized and converted into ammonium paratungstate. As a rule, scrap of cutting steels is disposed of at the enterprise that produces the same steels. Scrap from electrodes, incandescent lamps and chemicals is almost never recycled.

Tungsten is a chemical element of the 4th group, having atomic number 74 in the periodic system of Dmitry Ivanovich Mendeleev, denoted by W (Wolframium). The metal was discovered and isolated by two Spanish chemists, the d'Eluyar brothers, in 1783. The name "Wolframium" itself was transferred to an element from the previously known mineral wolframite, which was known back in the 16th century, it was then called "wolf foam", or "Spuma lupi" in Latin, in German this phrase sounds like "Wolf Rahm" (Tungsten). The name was associated with the fact that tungsten, during the maintenance of tin ores, significantly interfered with the smelting of tin, because. translated tin into slag foam (they began to say about this process: “Tin devours like a wolf a sheep!”). Currently, in the USA, France, Great Britain and some other countries, the name "tungsten" (from the Swedish tung sten, which translates as "heavy stone") is used to name tungsten.

Tungsten is a gray hard transition metal. The main application of tungsten is the role of the base in refractory materials in metallurgy. Tungsten is extremely refractory, under normal conditions the metal is chemically resistant.

Tungsten differs from all other metals in its unusual hardness, heaviness and infusibility. Since ancient times, there has been an expression among the people “heavy as lead” or “heavier than lead”, “lead eyelids”, etc. But it would be more correct to use the word "tungsten" in these allegories. The density of this metal is almost twice that of lead, to be precise, 1.7 times. With all this, the atomic mass of tungsten is lower and has a value of 184 versus 207 for lead.

Tungsten is a light gray metal, the melting and boiling points of this metal are the highest. Due to the plasticity and infusibility of tungsten, it is possible to use it as filaments in lighting devices, in kinescopes, and also in other vacuum tubes.

Twenty tungsten minerals are known. The most common: minerals of the wolframite scheelite group, which are of industrial importance. Less common is wolframite sulfide, i.e. tungstensite (WS2) and oxide-like compounds - ferro - and cuprotungstite, tungstite, hydrotungstite. Vads, psilomelans with a high content of tungsten, are widely distributed.

Depending on the conditions of occurrence, morphology and type of tungsten deposits, open, underground, and combined methods are used in their development.

Currently, there are no methods for obtaining tungsten directly from concentrates. In this regard, intermediate compounds are first isolated from the concentrate, and then metallic tungsten is obtained from them. The isolation of tungsten includes: the decomposition of concentrates, then the transition of the metal into compounds, from which it is separated from the rest of the accompanying elements. Isolation of tungstic acid, i.e. pure chemical compound tungsten, continues with the subsequent production of tungsten in metallic form.

Tungsten is used in the manufacture of machinery and equipment in the metalworking, construction and mining industries, in the manufacture of lamps and lamps, in the transport and electronics industries, in the chemical industry and other fields.

Made of tungsten steel, the tool is able to withstand the enormous speeds of the most intensive processes in metalworking. The cutting speed using such a tool is usually measured in tens of meters per second.

Tungsten is rather poorly distributed in nature. The content of metal in the earth's crust by mass is about 1.3·10 −4%. The main minerals containing tungsten are natural tungstates: scheelite, originally called tungsten, and wolframite.

Biological properties

The biological role of tungsten is insignificant. Tungsten is very similar to molybdenum in its properties, but, unlike the latter, tungsten is not an essential element. Despite this fact, tungsten is quite capable of replacing molybdenum in animals and plants, in the composition of bacteria, while it inhibits the activity of Mo-dependent enzymes, for example, xanthine oxidase. Due to the accumulation of tungsten salts in animals, uric acid levels decrease and hypoxanthine and xanthine levels increase. Tungsten dust, like other metal dusts, irritates the respiratory organs.

About 0.001-0.015 milligrams of tungsten enters the human body on average per day with food. The digestibility of the element itself, as well as tungsten salts, in the human gastrointestinal tract is 1-10%, poorly soluble tungstic acids - up to 20%. Tungsten mainly accumulates in bone tissue and kidneys. The bones contain approximately 0.00025 mg / kg, and in human blood about 0.001 mg / l of tungsten. The metal is usually excreted from the body naturally, in the urine. But 75% of the radioactive isotope of tungsten 185W is excreted in the feces.

Food sources of tungsten, as well as its daily requirement, have not yet been studied. The toxic dose for the human body has not yet been identified. Lethal outcome in rats occurs from a little more than 30 mg of the substance. In medicine, it is believed that tungsten does not have metabolic, carcinogenic and teratogenic effects on humans and animals.

Indicator of the elemental status of tungsten inside the human body: urine, whole blood. There are no data on the decrease in the level of tungsten in the blood.

An increased content of tungsten in the body most often occurs in workers of metallurgical plants engaged in the production of refractory and heat-resistant materials, alloyed steels, as well as in people who have come into contact with tungsten carbide.

The clinical syndrome "heavy metal disease" or pneumoconiosis can be the result of chronic intake of tungsten dust into the body. Signs can include coughing, breathing problems, atopic asthma, and changes inside the lungs. The above syndromes usually subside after a long rest, and simply in the absence of direct contact with vanadium. In the most severe cases, with a belated diagnosis of the disease, the pathology "cor pulmonale", emphysema and pulmonary fibrosis develop.

"Heavy metal diseases" and the prerequisites for its occurrence usually appear as a result of exposure to several types of metals and salts (for example, cobalt, tungsten, etc.). It has been found that the combined effect of tungsten and cobalt on the human body enhances the detrimental effect on the pulmonary system. The combination of tungsten and cobalt carbides can cause local inflammation and contact dermatitis.

At the present stage of development of medicine, there is no effective ways accelerated metabolism or excretion of a group of metal compounds that can provoke the appearance of "heavy metal disease". That is why it is so important to constantly carry out preventive measures and timely identify people with high sensitivity to heavy metals, to diagnose at the initial stage of the disease. All these factors determine the further chances for the success of the treatment of pathology. But in some cases, if necessary, therapy with complexing agents and symptomatic treatment is used.

More than half (more precisely 58%) of all tungsten produced is used in the manufacture of tungsten carbide, and almost a quarter (more precisely, 23%) is used in the production of various steels and alloys. The production of tungsten “rolled products” (this includes incandescent lamp filaments, electrical contacts, etc.) accounts for approximately 8% of the tungsten consumed in the world, and the remaining 9% is used to produce catalysts and pigments.

Tungsten wire, which has found application in electric lamps, has recently acquired a new profile: it has been proposed to use it as a cutting tool in the processing of brittle materials.

The high strength and good ductility of tungsten make it possible to produce unique items from it. For example, a wire so thin can be drawn from this metal that 100 km of this wire will have a mass of only 250 kg.

Molten liquid tungsten could remain in this state even near the surface of the Sun itself, because the boiling point of the metal is above 5500 °C.

Many people know that bronze is composed of copper, zinc and tin. But, the so-called tungsten bronze is not only not bronze by definition, because. does not contain any of the above metals, it is not an alloy at all, because. it lacks purely metallic compounds, and sodium and tungsten are oxidized.

Getting peach paint was very difficult, and often completely impossible. This is neither red nor pink, but some kind of intermediate, and even with a greenish tint. Giving says that more than 8,000 attempts had to be made to obtain this paint. In the 17th century, only the most expensive porcelain items for the then Chinese emperor were decorated with peach paint at a special factory in Shanxi province. But when, after some time, it was possible to reveal the secret of a rare paint, it turned out that it was based on nothing more than tungsten oxide.

This happened in 1911. A student named Li came to Yunnan Province from Beijing. Day after day he was lost in the mountains, trying to find some kind of stone, as he explained, it was a tin stone. But he didn't succeed. The owner of the house in which the student Li settled, lived with a young daughter named Xiao-mi. The girl was very sorry for the unfortunate student and in the evening, during dinner, she told him simple simple stories. One story told of an unusual stove that was built from some kind of dark stones that were torn off a cliff and laid in the backyard of their house. This stove turned out to be quite successful, and most importantly durable, for many years it regularly served the owners. Young Xiao-mi even gave the student even one such stone as a gift. It was a run-in, heavy, brown stone, like lead. Later it turned out that this stone was pure wolframite...

In 1900, at the opening of the world metallurgical exhibition in Paris, completely new specimens of high-speed steel (an alloy of steel with tungsten) were demonstrated for the first time. Literally immediately after that, tungsten began to be widely used in metallurgical industry all highly developed countries. But there are quite interesting fact: for the first time tungsten steel was invented in Russia in 1865 at the Motovilikha plant in the Urals.

In early 2010, an interesting artifact fell into the hands of Perm ufologists. It's supposed to be a wreck spaceship. The analysis of the fragment showed that the object consists almost entirely of pure tungsten. Only 0.1% of the composition falls on rare impurities. According to scientists, rocket nozzles are made from pure tungsten. But so far one fact has not been explained. In air, tungsten quickly oxidizes and rusts. But for some reason this fragment does not lend itself to corrosion.

Story

The word "tungsten" itself is of German origin. Previously, not the metal itself was called tungsten, but its main mineral, i.e. to wolframite. Some suggest that then this word was used almost as a swear word. From the beginning of the 16th to the second half of the 17th century, tungsten was considered a tin mineral. Although it does quite often accompany tin ores. But from ores, which included wolframite, tin was smelted much less. As if someone or something "devoured" useful tin. Hence the name of the new element. In German, Wolf (Wolf) means wolf, and Ram (Ramm) translated from ancient German means ram. Those. the expression "eats tin like a wolf eats a lamb", and became the name of the metal.

The well-known US chemical abstract journal or reference books on all the chemical elements of Mellor (England) and Pascal (France) do not even contain a mention of such an element as tungsten. The chemical element at number 74 is called tungsten. The symbol W, which stands for tungsten, has become widespread only in the last few years. In France and Italy, quite recently, the element was denoted by the letters Tu, i.e. the first letters of the word tungstene.

The foundations of such confusion are laid in the history of the discovery of the element. In 1783, the Spanish chemists, the Eluard brothers, reported that they had discovered a new chemical element. In the process of decomposition of the Saxon mineral "tungsten" with nitric acid, they managed to obtain "acidic earth", i.e. yellow precipitate of the oxide of an unknown metal, the precipitate was soluble in ammonia. In the starting material, this oxide was present together with oxides of manganese and iron. The Eluard brothers named this element tungsten, and the mineral from which the metal was mined wolframite.

But the Eluard brothers cannot be 100% called the discoverers of tungsten. Of course, they were the first to report their discovery in print, but ... In 1781, two years before the discovery of the brothers, the famous Swedish chemist Carl Wilhelm Scheele found exactly the same "yellow earth" in the process of treating another mineral with nitric acid. His scientist called it simply "tungsten" (translated from Swedish tung - heavy, sten - stone, i.e. "heavy stone"). Karl Wilhelm Scheele found that "yellow earth" differs in its color, as well as in other properties, from similar molybdenum. The scientist also learned that in the mineral itself, it was associated with calcium oxide. In honor of Scheele, the name of the mineral "tungsten" was changed to "scheelite". Interestingly, one of the Eluard brothers was a student of Scheele, in 1781 he worked in the teacher's laboratory. Neither Scheele nor the Eluard brothers began to share the discovery. Scheele simply did not claim this discovery, and the Eluard brothers did not insist on the priority of their superiority.

Many have heard of the so-called "tungsten bronzes". These are very beautiful looking metals. Blue tungsten bronze has the following composition Na2O WO2 , and golden bronze has the following composition 4WO3Na2O WO2 WO3; violet and purplish red are intermediate, with a WO3 to WO2 ratio of less than four and greater than one. As the formulas show, these substances contain neither tin, nor copper, nor zinc. These are not bronzes, and not alloys at all, because. they do not even have metal compounds, and sodium and tungsten are oxidized here. Such "bronzes" resemble real bronze not only in appearance, but also in their properties: hardness, resistance to chemicals, high electrical conductivity.

In ancient times, peach color was one of the rarest, it was said that 8000 experiments had to be carried out to obtain it. In the 17th century, the most expensive porcelain of the Chinese emperor was painted in peach color. But after revealing the secret of this paint, it suddenly turned out that it was based on tungsten oxide.

Being in nature

Tungsten is poorly distributed in nature, the metal content in the earth's crust is 1.3 10 -4% by weight. Tungsten is mainly found as part of complex oxidized compounds, which are formed by tungsten trioxide WO3, as well as oxides of iron and calcium or manganese, sometimes copper, lead, thorium and various rare earth elements. The most common mineral wolframite is a solid solution of tungstates, i.e. salts of tungstic acid, manganese and iron (nMnWO 4 mFeWO 4). The solution is solid and heavy crystals of black or brown color, depending on the predominance of various compounds in the composition of the solution. If there are more manganese compounds (huebnerite), the crystals will be black, if iron compounds (ferberite) predominate, the solution will be brown. Wolframite is an excellent conductor of electricity and is paramagnetic.

As for other tungsten minerals, scheelite is of industrial importance, i.e. calcium tungstate (formula CaWO 4). The mineral forms brilliant crystals of light yellow and sometimes almost white colors. Sheelite is not at all magnetic, but it has another feature - the ability to luminesce. After UV illumination in the dark, it will fluoresce bright blue. The presence of an admixture of molybdenum changes the color of the glow, it changes to pale blue, sometimes to cream. Thanks to this property, it is possible to easily detect geological deposits of the mineral.

Typically, deposits of tungsten ore are associated with the area of ​​distribution of granite. Large crystals of scheelite or wolframite are very rare. Usually minerals are simply interspersed in granitic rocks. Extracting tungsten from granite is quite difficult, because. its concentration is usually not more than 2%. In total, no more than 20 tungsten minerals are known. Among them, stolcite and rasoite can be distinguished, which are two different crystalline modifications of lead tungstate PbWO 4 . The remaining minerals are decomposition products or secondary forms of ordinary minerals, for example, scheelite and wolframite (hydrotungstite, which is hydrated tungsten oxide, was formed from wolframite; tungsten ocher), russelite, a mineral containing oxides of tungsten and bismuth. Tungstenite (WS 2) is the only non-oxide mineral of tungsten, and its main reserves are located in the USA. As a rule, the content of tungsten is in the range from 0.3% to 1.0% WO 3 .

All tungsten deposits are of hydrothermal or magmatic origin. Scheelite and wolframite are often found in the form of veins, in places where magma has penetrated into cracks in the earth's crust. The main part of tungsten deposits is concentrated in areas of young mountain ranges - the Alps, the Himalayas and the Pacific belt. The largest deposits of wolframite and scheelite are located in China, Burma, the USA, Russia (Urals, Transbaikalia and the Caucasus), Portugal and Bolivia. Annual extraction of tungsten ores in the world is approximately 5.95·104 tons of metal, of which 49.5·104 tons (or 83%) is extracted in China. About 3,400 tons per year are mined in Russia, and 3,000 tons per year in Canada.

The role of the global leader in the development of tungsten raw materials is played by China (the Jianshi field accounts for 60 percent of Chinese production, Hunan - 20 percent, Yunnan - 8 percent, Guangdong - 6 percent, Inner Mongolia and Guanzhi - 2% each, there are others). In Russia, the largest deposits of tungsten ore are located in 2 regions: in the North Caucasus (Tyrnyauz, Kabardino-Balkaria) and in the Far East. The plant in Nalchik processes tungsten ore into ammonium paratungstate and tungsten oxide.

The largest consumer of tungsten is Western Europe (30%). USA and China - 25% each, 12% -13% - Japan. About 3,000 tons of metal are consumed annually in the CIS.

Application

In total, about 30 thousand tons of tungsten are produced in the world per year. Tungsten steel and other alloys containing tungsten and its carbides are used in the manufacture of tank armor, shells and torpedo shells, the most important parts of aircraft and internal combustion engines.

The best tool steels contain tungsten. Metallurgy absorbs in general about 95% of all tungsten produced. What is typical for metallurgy is that not only pure tungsten is used, but tungsten is mainly used, which is cheaper - ferrotungsten, i.e. an alloy containing about 80% tungsten and about 20% iron. It is produced in electric arc furnaces.

Tungsten alloys have a number of remarkable qualities. An alloy of tungsten, copper and nickel, as it is also called a "heavy" metal, is a raw material in the manufacture of containers for storing radioactive substances. The protective effect of such an alloy is 40% higher than that of lead. Such an alloy is also used in radiotherapy, because with a relatively small thickness of the screen, quite sufficient protection is provided.

An alloy of tungsten carbide and 16% cobalt has such a hardness that it partially replaces diamond in well drilling. Pseudo-alloys of tungsten with silver and copper are an excellent material for switches and knife switches in high voltage environments. Such products last 6 times longer than conventional copper contacts.

The use of pure tungsten or alloys containing tungsten is based largely on their hardness, refractoriness and chemical resistance. Tungsten in its pure form is widely used in the production of filaments for electric incandescent lamps, as well as cathode ray tubes; used as windings and heating elements of electric furnaces, as well as a structural material for space and aircraft that operate at high temperatures.

Tungsten is part of the alloys of high-speed steels (tungsten content 17.5 - 18.5%), stellites (from cobalt with Cr, C, W additives), hastalloys (stainless steels based on Ni), as well as many other alloys. Tungsten is used as a basis in the production of heat-resistant and tool alloys, namely, ferrotungsten (W 68–86%, Mo and iron up to 7%) is used, which is easily obtained by direct reduction of scheelite or wolframite concentrate. Tungsten is used in the production of Pobeda. This is a superhard alloy, which contains 80–85% tungsten, 7–14% cobalt, 5–6% carbon. Pobedit is simply indispensable in the metalworking process, as well as in the oil and mining industries.

Magnesium and calcium tungstates are widely used in fluorescent devices. Other tungsten salts are used in the tanning and chemical industries. Tungsten disulfide is a dry high-temperature lubricant that is stable at temperatures up to 500°C. Tungsten bronzes and other tungsten compounds are used in the manufacture of paints. Quite a lot of tungsten compounds are excellent catalysts.

In the production of electric lamps, tungsten is indispensable because it is not only unusually refractory, but also quite plastic. 1 kg of tungsten serves as a raw material for the manufacture of 3.5 km of wire. Those. 1 kg of tungsten can be used to make filaments for 23,000 60-watt lamps. Only thanks to this property, the electrical industry around the world consumes about a hundred tons of tungsten per year.

Production

The first stage in the production of tungsten is the enrichment of the ore, i.e. separation of valuable components from the main ore mass, waste rock. The same concentration methods are used as for other heavy metal ores: grinding and flotation, followed by magnetic separation (wolframite ores) and oxidative roasting. The concentrate obtained by this method is usually burned with an excess of soda, thereby bringing tungsten into a soluble state, i.e. to sodium wolframite.

Another method for obtaining this substance is leaching. Tungsten is extracted with a soda solution at elevated temperature and under pressure, followed by neutralization and precipitation of calcium tungstate, i.e. scheelite. Scheelite is obtained because it is quite easy to extract purified tungsten oxide from it.

CaWO 4 → H 2 WO 4 or (NH 4) 2 WO 4 → WO 3

Tungsten oxide is also obtained through chlorides. The tungsten concentrate is treated with chlorine gas at an elevated temperature. In this case, tungsten chlorides are formed, which are easily separated from other chlorides by sublimation. The resulting chloride can be used to obtain oxide or immediately extract metal from it.

In the next step, the oxides and chlorides are converted into metallic tungsten. To reduce tungsten oxide, it is best to use hydrogen. With this reduction, the metal is the purest. The reduction of the oxide takes place in a special tube furnace, where the "boat" with WO 3 moves through several temperature zones. Dry hydrogen enters towards the "boat". Oxide reduction occurs in hot (450-600°C) and cold zones (750-1100°C). In cold zones, reduction to WO 2 occurs, and then to metal. As time passes through the hot zone, the grains of powdered tungsten change their size.

Recovery can take place not only under the supply of hydrogen. Coal is often used. Due to the solid reducing agent production is simplified, but the temperature in this case should reach 1300°C. Coal itself and the impurities that it always contains, reacting with tungsten, form carbides of other compounds. As a result, the metal is contaminated. But in the electrical industry, only high-quality tungsten is used. Even 0.1% iron impurities make tungsten for the manufacture of the thinnest wire, because. it becomes much more fragile.

The isolation of tungsten from chlorides is based on pyrolysis. Tungsten and chlorine form some compounds. An excess of chlorine allows all of them to be converted into WCl6, and it, in turn, at a temperature of 1600 ° C decomposes into chlorine and tungsten. If hydrogen is present, the process starts at 1000°C.

This is how tungsten is obtained in the form of a powder, which is then pressed at high temperature in a stream of hydrogen. The first stage of pressing (heating to about 1100-1300°C) produces a brittle porous ingot. Then the pressing continues, and the temperature begins to rise almost to the melting point of tungsten. In such an environment, the metal begins to become solid and gradually acquires its qualities and properties.

On average, 30% of the industrially produced tungsten is recycled tungsten. Tungsten scrap, sawdust, shavings and powder are oxidized and converted into ammonium paratungstate. As a rule, scrap of cutting steels is disposed of at the enterprise that produces the same steels. Scrap from electrodes, incandescent lamps and chemicals is almost never recycled.

In the Russian Federation, tungsten products are produced at: Skopinsky Hydrometallurgical Plant Metallurg, Vladikavkaz Plant Pobedit, Nalchik Hydrometallurgical Plant, Kirovgrad Hard Alloy Plant, Elektrostal, Chelyabinsk Electrometallurgical Plant.

Physical properties

Tungsten is a light gray metal. It has the highest melting point of any known element except carbon. The value of this indicator is approximately from 3387 to 3422 degrees Celsius. Tungsten has excellent mechanical properties when reaching high temperatures; among all metals, tungsten has the lowest value of such an indicator as the coefficient of expansion.

Tungsten is one of the heaviest metals, its density is 19250 kg/m3. The metal has a cubic body-centered lattice parameter a = 0.31589 nm. At a temperature of 0 degrees Celsius, the electrical conductivity of tungsten is only 28% of the value of the same indicator for silver (silver conducts current better than any other metal). Pure tungsten is very easy to process, but it is rare in its pure form, more often it has impurities of carbon and oxygen, due to which it gets its well-known hardness. The electrical resistance of the metal at a temperature of 20 degrees Celsius leaves 5.5 * 10 -4, at a temperature of 2700 degrees Celsius - 90.4 * 10 -4.

Tungsten differs from all other metals in its special infusibility, heaviness and hardness. The density of this metal is almost twice that of the same lead, or rather 1.7 times. But the atomic mass of the element, on the contrary, is lower and is 184 versus 207.

The values ​​of the tensile and compression moduli of tungsten are unusually high, the resistance to thermal creep is enormous, the metal has high electrical and thermal conductivity. Tungsten has a fairly high coefficient electronic emission, which can be significantly improved by alloying the element with oxides of some other metals.

The color of the resulting tungsten largely depends on the method of its production. Fused tungsten is a lustrous gray metal that looks a lot like platinum. Tungsten powder can be gray, dark gray and even black: the smaller the grains of the powder, the darker it will be.

Tungsten has a high resistance: at room temperature it does not change in air; when the temperature reaches red heat, the metal begins to slowly oxidize, releasing tungstic anhydride. Tungsten is almost insoluble in sulfuric, hydrofluoric and hydrochloric acids. In aqua regia and nitric acid, the metal is oxidized from the surface. Being in a mixture of hydrofluoric and nitric acid, tungsten dissolves, forming tungstic acid. Of all the tungsten compounds, the most practical benefits are: tungsten anhydride or tungsten trioxide, peroxides with the general formula ME2WOX, tungstates, compounds with carbon, sulfur and halogens.

Tungsten, found in nature, consists of 5 stable isotopes whose mass numbers are 186.184, 183, 182, 181. The most common isotope with a mass number of 184, its share is 30.64%. Of the entire relative set of artificial radioactive isotopes of element number 74, only three are of practical importance: tungsten-181 (its half-life is 145 days), tungsten-185 (its half-life is 74.5 days), tungsten-187 (its half-life is half-life is 23.85 hours). All these isotopes are produced within nuclear reactors in the process of shelling tungsten isotopes with neutrons of a natural mixture.

The valency of tungsten has a changeable character - from 2 to 6, the most stable is hexavalent tungsten, tri- and divalent compounds of a chemical element are unstable and have no practical value. The radius of a tungsten atom is 0.141 nm.

The clarke of tungsten in the earth's crust according to Vinogradov is 0.00013 g/t. Its average content in the composition rocks, grams/ton: ultrabasic - 0.00001, basic - 0.00007, medium - 0.00012, sour - 0.00019.

Chemical properties

Tungsten is not affected by: aqua regia, sulfuric, hydrochloric, hydrofluoric and nitric acids, an aqueous solution of sodium hydroxide, mercury, mercury vapor, ammonia (up to 700 ° C), air and oxygen (up to 400 ° C), hydrogen, water, hydrogen chloride (up to 600 ° C), carbon monoxide (up to 800 ° C), nitrogen.

Already after a slight heating, dry fluorine begins to combine with finely divided tungsten. As a result, hexafluoride is formed (formula WF 6) - this is a very interesting substance that has a melting point of 2.5 ° C and a boiling point of 19.5 ° C. After the reaction with chlorine, a similar compound is formed, but the reaction is possible only at a temperature of 600 ° C. WC16, steel blue crystals, melts at 275°C and boils at 347°C. Tungsten forms weakly stable compounds with iodine and bromine: tetra- and diiodide, penta- and dibromide.

At high temperatures, tungsten can combine with selenium, sulfur, nitrogen, boron, tellurium, silicon and carbon. Some of these compounds are remarkably hard, as well as other excellent qualities.

Of particular interest is carbonyl (formula W(CO) 6). Tungsten here combines with carbon monoxide, and, therefore, has a zero valency. Tungsten carbonyl is produced in special conditions, because he is extremely unstable. At a temperature of 0°C, it is released from a special solution in the form of colorless crystals; after reaching 50°C, the carbonyl sublimates; at 100°C, it completely decomposes. But it is thanks to this compound that dense and hard tungsten coatings (from pure tungsten) can be obtained. Many compounds of tungsten, like tungsten itself, are very active. For example, tungsten oxide tungsten oxide WO 3 has the ability to polymerize. In this case, the so-called heteropolycompounds (their molecules can contain more than 50 atoms) and isopolycompounds are formed.

Tungsten oxide (VI)WO 3 is a light yellow crystalline substance that turns orange when heated. The oxide has a melting point of 1473°C and a boiling point of 1800°C. Tungstic acid, corresponding to it, is not stable, in a solution of water the dihydrate precipitates, while it loses one molecule of water at a temperature of 70 to 100 ° C, and the second molecule at a temperature of 180 to 350 ° C.

Anions of tungstic acids tend to form polycompounds. As a result of the reaction with concentrated acids, mixed anhydrides are formed:

12WO 3 + H 3 PO 4 \u003d H 3.

As a result of the reaction of tungsten oxide and metallic sodium, a non-stoichiometric sodium tungstate is obtained, which is called "tungsten bronze":

WO 3 + xNa = Na x WO 3.

In the process of reducing tungsten oxide with hydrogen, hydrated oxides are obtained during isolation, having a mixed oxidation state, they are called "tungsten blue":

WO 3–n (OH) n, n = 0.5–0.1.

WO 3 + Zn + HCl = ("blue"), W 2 O 5 (OH) (brown)

Tungsten(VI) oxide is an intermediate in manufacturing process tungsten and its compounds. It is a component of certain ceramic pigments and industrially important hydrogenation catalysts.

WCl 6 - Higher tungsten chloride, formed as a result of the interaction of metallic tungsten or tungsten oxide with chlorine, fluorine, or carbon tetrachloride. After the reduction of tungsten chloride with aluminum, tungsten carbonyl is formed together with carbon monoxide:

WCl 6 + 2Al + 6CO = + 2AlCl 3 (in ether)

Tungsten is refractory metal . It has its own varieties of brands, each of which has its own characteristics. This element in periodic table Mendeleev is number 74 and has a light gray color. Its melting point is 3380 degrees. Its main properties are the coefficient of linear expansion, electrical resistance, melting point and density.

Properties and grades of tungsten

Tungsten has its own mechanical and physical properties, as well as several varieties of grades.

To physical properties include:

Mechanical properties:

• Relative elongation - 0%.
• Tensile strength - 800−1100 MPa.
• Poisson's ratio 0.29.
• Shear modulus - 151.0 GPa.
• Modulus of elasticity - 415.0 GPa.

This metal is distinguished by a low evaporation rate even at 2 thousand degrees and a very large boiling point - 5900 degrees. The properties that limit the use of this material are low oxidation resistance, high brittleness and high density. It looks like steel. Used to produce high strength alloys. It can be processed only after heating. The heating temperature depends on which processing method you are going to carry out.

Tungsten has the following grades:

Application area

Because of its unique properties, tungsten has been widely used. In industry, it is used in pure form and in alloys.

Main Applications are:

Production process of refractory tungsten

This material is classified as a rare metal. It is characterized by relatively small volumes of consumption and production, as well as a low prevalence in the earth's crust. none of rare metals are not obtained by recovery from raw materials. Initially, it is processed into a chemical compound. And any rare metal ore is subjected to additional enrichment before processing.

There are three main stages for obtaining a rare metal:

1. The decomposition of the ore. The extracted metal is separated from the bulk of the processed raw material. It is concentrated in the precipitate or solution.
2. Obtaining a chemically pure compound. Its isolation and purification.
3. A metal is isolated from the resulting compound. Thus, pure materials without impurities are obtained.

In the process of obtaining tungsten, too there are several stages. The initial raw material is scheelite and wolframite. Typically, their composition contains from 0.2 to 2% tungsten.

1. Ore enrichment is carried out using electrostatic or magnetic separation, flotation, gravity. As a result, a tungsten concentrate is obtained, which contains approximately 55–65% tungsten anhydride. The presence of impurities is also controlled in them: bismuth, antimony, copper, tin, arsenic, sulfur, phosphorus.
2. Obtaining tungsten anhydride. It is a raw material for the manufacture of metal tungsten or its carbide. To do this, a number of procedures are carried out, such as: leaching of cake and alloy, decomposition of concentrates, production of tungstic technical acid, and others. As a result of these actions, a product should be obtained that will contain 99.9% tungsten trioxide.
3. Getting the powder. In powder form, pure metal can be obtained from the anhydride. For this, reduction is carried out with carbon or hydrogen. Carbon reduction is carried out less frequently because the anhydride is saturated with carbides and this leads to metal brittleness and poor processing. When obtaining a powder, special methods are used that allow you to control the shape and size of grains, granulometric and chemical compositions.
4. Obtaining compact tungsten. Basically, in the form of ingots or rods, it is a blank for the manufacture of semi-finished products: tape, rods, wire, and others.

Tungsten products

Tungsten is used to make many items necessary for the economy, such as wire, rods and others.

bars

One of the most common products made from this refractory material is tungsten rods. The starting material for its manufacture is a rod.

To get a rod from a rod, it is forged using a rotary forging machine.

Forging is carried out when heated, since this metal is very brittle at room temperature. There are several stages in forging. On each subsequent bars, smaller diameters are obtained.

At the first stage, bars are obtained that will have a diameter of up to 7 millimeters if the rod has a length of 10 to 15 centimeters. The temperature of the workpiece during forging should be 1450-1500 degrees. The heating material is usually molybdenum. After the second stage, the bars will be up to 4.5 millimeters in diameter. The temperature of the rod during its production is approximately 1250-1300 degrees. At the next stage, the bars will have a diameter of up to 2.75 millimeters.

Bars of grades VCh and VA are produced at lower temperatures than grades VI, VL and VT.

If the workpiece was obtained by melting, then hot forging is not carried out. This is due to the fact that such ingots have a coarse crystalline structure. When using hot forging, fractures and cracks may appear.

In this situation tungsten ingots subjected to hot double pressing (approximate degree of deformation 90%). The first pressing is carried out at a temperature of 1800-1900 degrees, and the second - 1350-1500. After that, the blanks are hot forged in order to obtain tungsten rods from them.

These products are used in many industries. One of the most common is welding non-consumable electrodes. For them, rods that are made of grades VL, VL and VT are suitable. Rods made of grades MV, VR and VA are used as heaters. They are used in furnaces, the temperature of which can reach 3 thousand degrees in a vacuum, inert gas or hydrogen atmosphere. Tungsten rods can be used as cathodes for gas-charging and electronic devices, as well as radio tubes.

electrodes

One of the main components that are necessary for welding are welding electrodes. In arc welding, they are most widely used. It belongs to the thermal class of welding, in which melting is carried out due to thermal energy. Automatic, semi-automatic or manual arc welding is the most common. A voltaic arc is created thermal energy, which is located between the product and the electrode. An arc is called a stable powerful electric charge in an ionized atmosphere of metal vapors, gases. To create an arc, the electrode conducts an electric current to the welding site.

The welding electrode is called a wire rod, on which a coating is applied (variants are also possible without coating). There are many different electrodes for welding. Them hallmarks are diameter, length, chemical composition. Different electrodes are used for welding certain alloys or metals. The most important type of classification is the division of electrodes into non-consumable and consumable.

Welding consumable electrodes during welding, they are melted, their metal, together with the metal of the molten part being welded, replenishes the weld pool. Such electrodes are made of copper and steel.

But non-consumable electrodes do not melt during welding. These include tungsten and carbon electrodes. When welding, it is necessary to supply a filler material that melts and forms a weld pool with the molten material of the welded element. For these purposes, mainly used welding rods or wire. Welding electrodes can be uncoated and coated. Cover plays important role. Its components can ensure the production of weld metal of certain properties and composition, protection of the molten metal from the influence of air and stable arc burning.

The constituents in the coating may be deoxidizing, slag-forming, gas-forming, stabilizing or alloying. The coating can be cellulosic, basic, rutile or acidic.

Tungsten electrodes are used for welding non-ferrous metals, as well as their alloys, high-alloy steels. Good tungsten electrode is suitable for education weld increased strength, while the parts may have a different chemical composition.

Tungsten products are of very high quality and have found their application in many industries, in some they are simply irreplaceable.

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

SEVERSKY TECHNOLOGICAL INSTITUTE - branch

federal state autonomous educational institution

higher professional education

"National Research Nuclear University "MEPhI"

Department of ChiTMSE

TUNGSTEN

abstract on discipline

"Selected Chapters on the Chemistry of the Elements"

Student gr. D-143

Androsov V. O.

"____" ___________ 2014

checked

Associate Professor of the Department of ChiTMSE

Bezrukova S.A.

"____" _________ 2014

Seversk 2014

Introduction

History of the origin of the name

Receipt

Physical properties

Chemical properties

1. Application

   1. Metal tungsten

      Tungsten compounds

Biological role

Conclusion

Bibliography

Introduction

Tungsten is a chemical element with atomic number 74 in the Periodic Table of Chemical Elements of D. I. Mendeleev, denoted by the symbol W (lat. Wolframium). Under normal conditions, it is a hard, shiny, silver-gray transition metal.

Tungsten is the most refractory of the metals. Only the non-metallic element, carbon, has a higher melting point. Under standard conditions, chemically resistant.

History of the origin of the name

The name Wolframium was transferred to the element from the mineral wolframite, known as far back as the 16th century. called "wolf foam" - "Spuma lupi" in Latin, or "Wolf Rahm" in German. The name was due to the fact that tungsten, accompanying tin ores, interfered with the smelting of tin, turning it into foam of slag (“it devours tin like a wolf a sheep”).

Currently, in the USA, Great Britain and France, the name "tungsten" (Swedish tung sten - "heavy stone") is used for tungsten.

In 1781, the famous Swedish chemist Scheele, treating the mineral scheelite with nitric acid, obtained a yellow “heavy stone” (tungsten trioxide). In 1783, the Spanish chemists, the Eluard brothers, reported obtaining from the Saxon mineral wolframite both a yellow oxide of a new metal soluble in ammonia and the metal itself. At the same time, one of the brothers, Fausto, was in Sweden in 1781 and communicated with Scheele. Scheele did not claim to discover tungsten, and the Eluard brothers did not insist on their priority.

Receipt

Wolframite and scheelite concentrates (50-60% WO 3) serve as raw materials for the production of Tungsten.

Ferrotungsten (an alloy of iron with 65-80% Tungsten) is directly smelted from concentrates, which is used in steel production; to obtain Tungsten, its alloys and compounds, tungsten anhydride is isolated from the concentrate.

In industry, several methods are used to obtain WO 3:

1. Scheelite concentrates are decomposed in autoclaves with a soda solution at 180-200 ° C (a technical solution of sodium tungstate is obtained) or hydrochloric acid (a technical tungstic acid is obtained):

1. CaWO 4 (tv) + Na 2 CO 3 (l) = Na 2 WO 4 (l) + CaCO 3 (tv)

2. CaWO 4 (tv) + 2 HCl (l) \u003d H 2 WO 4 (tv) + CaCl 2 (solution).

Wolframite concentrates are decomposed either by sintering with soda at 800-900°C, followed by leaching of Na 2 WO 4 with water, or by treatment with sodium hydroxide solution when heated. When decomposed by alkaline agents (soda or caustic soda), a solution of Na 2 WO 4 is formed, contaminated with impurities. After their separation from the solution emit H 2 WO 4 . To obtain coarser, easily filterable and washable precipitates, CaWO 4 is first precipitated from a Na 2 WO 4 solution, which is then decomposed with hydrochloric acid. Dried H 2 WO 4 contains 0.2 - 0.3% impurities.

By calcining H 2 WO 4 at 700-800 ° C, WO 3 is obtained, and from it hard alloys are obtained.

2. For the production of metallic Tungsten, H 2 WO 4 is additionally purified by the ammonia method - by dissolving in ammonia and crystallizing ammonium paratungstate 5 (NH 4) 2 O 12WO 3 nH 2 O. Calcining this salt gives pure WO 3.

3. Tungsten powder is obtained by reducing WO 3 with hydrogen (and in the production of hard alloys - also with carbon) in tubular electric furnaces at 700-850°C. Compact metal is obtained from powder by the cermet method, that is, by pressing in steel molds under a pressure of 3000-5000 (kg * s / cm 2) and heat treatment of pressed blanks - rods. The last stage of heat treatment - heating up to about 3000°C is carried out in special apparatuses directly by passing electric current through the rod in a hydrogen atmosphere. As a result, tungsten is obtained, which lends itself well to pressure treatment (forging, drawing, rolling, etc.) when heated.

Physical properties

Tungsten is a shiny light gray metal with the highest proven melting and boiling points (it is assumed that seaborgium is even more refractory, but so far this cannot be firmly stated - the lifetime of seaborgium is very short). Melting point - 3695 K (3422 °C), boils at 5828 K (5555 °C). The density of pure tungsten is 19.25 g/cm³. It has paramagnetic properties. Brinell hardness 488 kg/mm², electrical resistivity at 20 °C - 55·10−9 Ohm·m, at 2700°C - 904·10−9 Ohm·m. It lends itself well to forging and can be drawn into a thin thread.

Chemical properties

It has valency II, III and VI. The most stable is valence tungsten VI. II, III valence compounds of tungsten are unstable and have no practical significance.

Under normal conditions Tungsten is chemically stable. At 400-500°C it is oxidized in air to WO 3 . Water vapor intensively oxidizes it above 600°C to WO 3 . Halogens, sulfur, carbon, silicon, boron interact with tungsten at high temperatures (fluorine with powdered tungsten - at room temperature). Tungsten does not react with hydrogen up to the melting point; with nitrogen above 1500°C forms nitride. Under normal conditions, Tungsten is resistant to hydrochloric, sulfuric, nitric and hydrofluoric acids, as well as to aqua regia; at 100°С, weakly interacts with them; dissolves rapidly in a mixture of hydrofluoric and nitric acids.

In alkali solutions, when heated, tungsten dissolves slightly, and in molten alkalis with access to air or in the presence of oxidizing agents - quickly; in this case, tungstates are formed.

Tungsten forms four oxides:

higher - WO 3 (tungsten anhydride),

lower - WO 2 and

two intermediate W 10 O 29 and W 4 O 11.

Tungstic anhydride is a lemon-yellow crystalline powder that dissolves in alkali solutions to form tungstates. When it is reduced with hydrogen, lower oxides and tungsten are successively formed.

Tungstic anhydride corresponds to tungstic acid H 2 WO 4 - a yellow powder, practically insoluble in water and acids. When it interacts with solutions of alkalis and ammonia, solutions of tungstates are formed. At 188°C H 2 WO 4 decomposes to form WO 3 and water.

With chlorine, tungsten forms a series of chlorides and oxychlorides. The most important of them: WCl 6 (tmelt 275°C, tbp 348°C) and WO 2 Cl 2 (tmelt 266°C, sublimates above 300°C), are obtained by the action of chlorine on tungsten anhydride in the presence of coal.

With sulfur, tungsten forms two sulfides WS 2 and WS 3 .

Tungsten carbides WC (tmelt 2900°C) and W 2 C (tmelt 2750°C) are hard refractory compounds; obtained by the interaction of Tungsten with carbon at 1000-1500°C

isotopes

Natural tungsten consists of five isotopes (180 W, 182 W, 183 W, 184 W and 186 W). Another 30 radionuclides have been artificially created and identified (Table 1). In 2003, the extremely weak radioactivity of natural tungsten was discovered (about two decays per gram of element per year), due to the α-activity of 180 W, which has a half-life of 1.8 × 10 18 years

Table 1.

Symbolnuclide			Isotope mass (a.u.m.)	Half-life(T 1/2 )		Spin the parity of the nucleus
	Excitation energy
				1.2 10 18 years
				stable
				stable
				stable
				stable

Application

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% of mined tungsten is used in tungsten steels, about 15% of tungsten is used for the production 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.

Metal tungsten

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 them. bad influence. As a result, steel with the addition of tungsten receives high hardness, refractoriness, elasticity and resistance to acids.

Everyone knows high quality blades made of Damascus steel, which contains a few percent of the admixture of tungsten. 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 heavy loads and have a much longer service life than rails made from conventional steels. A remarkable property of steel with the addition of 91.8% 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 from high speed steel are 35 times slower than carbide 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 substances - diamond, is expressed as 10 points (on the Mohs scale), then the hardness of tungsten carbide is 9.8. Among the superhard alloys is the well-known alloy of carbon with tungsten and the addition of cobalt - it will win. 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 (osmium, 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 was developed - atomic hydrogen, which made it possible to weld various steels, aluminum, copper and 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 also found application as a catalyst, with its help they 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

Tungsten trioxide(WO 3) is used to obtain tungsten carbides and halides, as a yellow pigment in the coloring of glass and ceramics. It is a catalyst for the hydrogenation and cracking of hydrocarbons.

Tungstic acid(H 2 WO 4) is used as a mordant and dye in the textile industry. Tungstic acid is an intermediate in the production of tungsten.

Wolfram carbide(WC) is actively used in engineering for the manufacture of tools that require high hardness and corrosion resistance, as well as for wear-resistant surfacing of parts operating under conditions of intense abrasive wear with moderate impact loads. This material is used in the manufacture of various cutters, abrasive discs, drills, cutters, drill bits and other cutting tools. The grade of carbide known as "win" is 90% tungsten carbide.