Chemical properties of tungsten. Features and use of tungsten
Tungsten refers to refractory metals, which are relatively common in the earth's crust. Thus, the content in the earth's crust (in%) of the tungsten of approximately 10 -5, rhenium 10 -7, molybdenum 3.10 -4, niobium 10 -3, tantalum 2.10 -4 and vanadium 1.5.10 -2.
The refractory metals are transitional elements and are arranged in IV, V, VI and VII groups (subgroup a) of the periodic system of elements. With an increase in the atomic number, the melting point of refractory metals increases in each of the subgroups.
Elements VA and VIA groups (vanadium, niobium, tantalum, chromium, molybdenum and tungsten) are refractory metals with a volume-centered cubic lattice, in contrast to other refractory metals having a grazent and hexagonal tightly packaged structure.
It is known that the main factor determining the crystal structure and physical properties of metals and alloys is the nature of their interatomic ties. The refractory metals are characterized by high strength of the interatomic bond and, as a result, high melting point, increased mechanical strength and significant electrical resistance.
The ability to study metals by electron microscopy allows you to study the structural features of the atomic scale, identifies the relationship between mechanical properties and dislocations, packaging defects, etc. The obtained data show that characteristic physical properties that distinguish with refractory metals from conventional are determined by the electronic structure of their atoms. Electrons can vary to varying degrees from one atom to another, while the type of transition corresponds to a certain type of interatomic communication. The feature of the electronic structure determines high level interatomic forces (ties), high melting point, metals strength and their interaction with other elements and impurities of implementation. In tungsten, the chemically active sheath for the energy level includes electrons 5 D and 6 s.
Of the refractory metals, the greatest density has tungsten - 19.3 g / cm 3. Although, when used in structures ^, a large tungsten density can be considered as a negative indicator, still increased strength at high temperatures reduces the mass of tungsten products by reducing their size.
The density of refractory metals to a large extent depends on their state. For example, the density of the sintered tungsten headacter varies in the range of 17.0-18.0 g / cm 3, and the density of the forged headacon with the degree of deformation is 75% is 18.6-19.2 g / cm 3. The same is observed in molybdenum: the sintered headacon has a density of 9.2-9.8 g / cm 3, forged with a degree of deformation 75% -9.7-10.2 g / cm 3 and 10.2 g / cm 3 .
Some physical properties of tungsten, tantalum, molybdenum and niobium for comparison are given in Table. 1. The thermal conductivity of tungsten is less than half of the thermal conductivity of copper, but it is much higher than iron or nickel.
The refractory metals of groups VA, VIA, VII of a periodic system of elements compared to other elements have a smaller linear extension coefficient. The smallest linear expansion coefficient has tungsten, which indicates the high stability of its atomic lattice and is the unique property of this metal.
Tungsten has a thermal conductivity of about 3 times smaller than the electrical conductivity of annealed copper, but it is higher than that of iron, platinum and phosphate bronze.
For metallurgy great importance It has a metal density in a liquid state, since this characteristic determines the speed of the channels through the channels, the process of removing gaseous and non-metallic inclusions and affects the formation of shock shell and porosity in the ingots. In tungsten, this value is higher than that of other refractory metals. However, another physical characteristic - surface tension Liquid refractory metals at melting point - differs less (see Table 1). Knowledge of this physical characteristics It is necessary at such processes as the application of protective coatings, when impregnating, smelting and casting.
An important casting property of metal is liquid process. If for all metals, this value is determined by pouring the liquid metal into a spiral shape at a fill temperature above the melting point by 100-200 ° C, then the fluid flow of tungsten was obtained by extrapolation of the empirical dependence of this value from the heat of melting.
Tungsten resistant in various gas media, acids and some molten metals. At room temperature, tungsten does not interact with hydrochloric, sulfuric and phosphoric acids, is not exposed to dissolved nitric acid and to a lesser extent than molybdenum, reacts to a mixture of nitric and hydrofluoric acids. Wolfram has a high corrosion resistance in some alkalisms, for example, in sodium and potassium hydroxide medium, in which there is a resistance to a temperature of 550 ° C. With the action of molten sodium, it is resistant to 900 ° C, mercury - up to 600 ° C, gallium up to 800 and Bismuth up to 980 ° C. Corrosion rate in these liquid metals does not exceed 0.025 mm / year. At a temperature of 400-490 ° C, tungsten begins to oxide in the air medium and in oxygen. A weak reaction occurs when heated to 100 ° C in hydrochloric, nitric and hydrofluoric acids. In the mixture of float and nitric acids there is a rapid dissolution of tungsten. Interaction gas media It starts at temperatures (° C): with chlorine 250, with fluorine 20. In carbon dioxide, tungsten is oxidized at 1200 ° C, the reaction does not occur in ammonia.
The pattern of oxidation of refractory metals is determined mainly temperature. Tungsten up to 800-1000 ° C has a parabolic pattern of oxidation, and over 1000 ° C - linear.
High corrosion resistance in liquid-metal media (sodium, potassium, lithium, mercury) allows you to use tungsten and its alloys in power plants.
The strength properties of tungsten depend on the state of the material and temperature. For forged rods tungsten, the tensile limit after recrystallization varies depending on the test temperature of 141 kgf / mm 2 at 20 ° C to 15.5 kgf / mm 2 at 1370 ° C. The tungsten powder metallurgy method with a temperature of from 1370 to 2205 ° C has? B \u003d 22,5? 6.3 kgf / mm 2. Tungsten strength is particularly increasing in the process of cold deformation. Wire with a diameter of 0.025 mm has a strength of 427 kgf / mm 2.
The hardness of the deformed technically pure tungsten HV 488, annealed HV 286. In this case, such a high hardness is preserved up to temperatures close to the melting point, and largely depends on the purity of the metal.
The modulus of elasticity is approximately associated with the atomic volume of melting point.
where T pl - the absolute melting point; V AT - atomic volume; K - constant.
A distinctive feature of tungsten among metals is also high volumetric deformation, which is determined from the expression
where e is the modulus of the elasticity of the first kind, kgf / mm 2; ? -Cheffer transverse deformation.
Table. 3 illustrates a change in volumetric deformation for steel, cast iron and tungsten, calculated according to the above expression.
The plasticity of the technically pure tungsten at 20 e C is less than 1% and grows after the zone electron beam purification from impurities, as well as when it is doping it with an additive of 2% thorium oxide. With increasing temperature, plasticity rises.
The greater energy of the interatomic bonds of metals of groups IV, V, VIA determines their high strength at room and elevated temperatures. The mechanical properties of refractory metals substantially depend on their purity, methods for producing, mechanical and heat treatment, the type of semi-finished products and other factors. Most of the information about the mechanical properties of refractory metals published in the literature are obtained on not enough clean metals, since the melting under vacuum conditions began to apply relatively recently.
In fig. 1 shows the dependence of the melting point of refractory metals from the position in periodic system Elements.
Comparison of the mechanical properties of tungsten after arc smelting and tungsten, obtained by powder metallurgy, shows that although their strength limit is slightly different, but more plastic turns out to be tungsten with arc smelting.
The hardness of the brinell tungsten in the form of a sintered headacker is a HV 200-250, and the laminated molded sheet of HB 450-500, the hardness of the molybdenum is equal to the HB of 150-160 and HB 240-250, respectively.
Tungsten doping is carried out in order to increase its plasticity, for this, it is primarily used by substitution elements. More attention is paid to attempts to increase the plasticization of metals of the VIA group by additives of small quantities of elements of groups VII and VIII. The increase in plasticity is explained by the fact that with doping transition metal additives in the alloy, an inhomogeneous electron density is created due to the localization of electrons of alloying elements. At the same time, the atom of the doping element changes the forces of the interatomic bond in the adjacent volume of the solvent; The length of this volume should depend on the electronic structure of the alloying and doped metals.
The difficulty of creating tungsten alloys is that it is not yet possible with increasing strength to provide the necessary plasticity. The mechanical properties of tungsten alloys doped with molybdenum, tantalum, niobium and thorium oxide (with short-term tests) are shown in Table. four.
The doping of tungsten molybdenum allows to obtain alloys, which in their strength properties are superior to illegated tungsten up to temperatures of 2200 ° C (see Table 4). With an increase in the content of tantalum from 1.6 to 3.6% at a temperature of 1650 ° C, the strength increases by 2.5 times. This is accompanied by a decrease by 2 times.
Dispersive strengthened and complex alloys based on tungsten, which contain molybdenum, niobium, hafnium, zirconium, carbon, are developed and mastering. For example, the following compositions: W - 3% Mo - 1% NB; W - 3% Mo - 0.1% HF; W - 3% Mo - 0.05% Zr; W - 0.07% Zr - 0.004% b; W - 25% Mo - 0.11% Zr - 0.05% C.
Alloy W - 0.48% ZR-0.048% C has? B \u003d 55.2 kgf / mm 2 at 1650 ° C and 43.8 kgf / mm 2 at 1925 ° C.
High mechanical properties have tungsten alloys containing thousandth fractions of the percent of boron, the tenths of the percentage of zirconium, and hafnium and about 1.5% niobium. The strength of these alloys on the gap at high temperatures is 54.6 kgf / mm 2 at 1650 ° C, 23.8 kgf / mm 2 at 2200 ° C and 4.6 kgf / mm 2 at 2760 ° C. However, the transition temperature (about 500 ° C) such alloys from the plastic state in fragile is sufficiently high.
The literature has information about tungsten alloys with 0.01 and 0.1% C, which are characterized by the limit of strength exceeding 2-3 times the strength of the recrystallized tungsten.
Rhenium significantly increases the heat resistance of tungsten alloys (Table 5).
A very long time ago and in a wide scale, tungsten and its alloys in electrical and electrovacuum techniques are used. Tungsten and its alloys are the main material for the manufacture of filaments of incandescent, electrodes, cathodes and other elements of the structures of powerful electrovacuum devices. High emission ability and light output in the rolled state, low elasticity of the steam make tungsten with one of the most important materials for this industry. In electrovacuum devices for the manufacture of parts operating at low temperatures, not passing pre-treatment at temperatures above 300 ° C, a clean (without additives) tungsten is used.
Additives of various elements significantly change the properties of tungsten. This makes it possible to create tungsten alloys with the necessary characteristics. For example, for parts of electrovacuum devices that require the use of non-writer tungsten at temperatures up to 2900 ° C and with high primary recrystallization temperature, alloys with silicular or aluminum additives are used. Silicone and thorium additives increase the recrystallization temperature and increase tungsten strength at high temperatures, which allows manufacturing parts operating at temperatures up to 2100 ° C under conditions of increased mechanical loads.
Cathodes of electronic and gas-discharge devices, hooks and springs of generator lamps in order to increase the emission properties are made of tungsten with an additive of thorium oxide (for example, BT-7 grades, W-10, W-15, with a thorium oxide content, respectively, 7, 10 and 15% ).
High temperature thermocouples are made of tungsten alloys with rhenium. Wolfram without additives, in which the increased content of impurities is allowed, used in the manufacture of cold parts of electrical accumulating devices (inputs in glass, traverse). Electrodes of pulsed lamps and cold cathodes of gas-discharge lamps are recommended to do from a tungsten alloy with nickel and barium.
To work at temperatures above 1700 ° C, the alloys of BB-2 (tungstenononoboy) should be applied. It is interesting to note that with short-term tests of alloys with a niobium content from 0.5 to 2% have a strength of 1650 ° C 2-2.5 times higher than illegated tungsten. Tungsten alloy with 15% molybdenum is the most durable. W-RE-TH O 2 alloys have good workability compared to alloys W - RE; Adding thorium dioxide makes it possible to process such as sharpening, milling, drilling.
The doping of tungsten rhenium increases its plasticity, the strength properties with increasing temperatures become approximately the same. Supplements in the alloys of the tungsten of fine oxides increase their plasticity. In addition, these additives greatly improve the machinability of cutting.
Tungsten alloys (W - 3% RE; W - 5% RE; W - 25% Re) are used to measure and control the temperature to 2480 ° C in the production of steel and in other types of equipment. The use of tungsten alloys with rhenium in the manufacture of anticatodes in X-ray tubes increases. Molybdenum anticatics covered with this alloy work under heavy load and have a longer service life.
The high sensitivity of tungsten electrodes to the change in the concentration of hydrogen ions allows them to be used for potentiometric titration. Such electrodes are used to control water and various solutions. They are easy to design and have a small amount of electrical resistance, which makes them promising their use as microelectrodes in the study of acid resistance of the athelectric layer in electrochemical processes.
The disadvantages of tungsten are its low plasticity (?<1%), большая плотность, высокое поперечное сечение захвата тепловых нейтронов, плохая свариваемость, низкая ока-линостойкость и плохая обрабатываемость резанием. Однако легирование его различными элементами позволяет улучшить эти характеристики.
A number of parts for the electrical industry and the nozzle engines inserts are made of tungsten, impregnated with copper or silver. The interaction of the refining solid phase (tungsten) with impregnating metal (copper or silver) is that the mutual solubility of metals is practically absent. The boundary angles of wetting tungsten liquid copper and silver are sufficiently small due to the large surface energy of tungsten, and this fact improves silver or copper penetration. Tungsten, soaked in silver or copper, was originally in two methods: the full immersion of the harvesting from tungsten into the molten metal or partial immersion of the suspended billet from tungsten. There are also impregnation methods using hydrostatic pressure of liquid or vacuum suction.
Making from tungsten electrical contacts impregnated with silver or copper, is carried out as follows. First, pressing the tungsten powder and sintering with certain technological modes. Then the resulting workpiece is impregnated. Depending on the porosity of the workpiece, the proportion of the impregnating substance changes. Thus, the copper content in tungsten may vary from 30 to 13% with a change in the specific pressure of the pressing of 2 to 20 ts / cm 2. The technology of obtaining impregnated materials is quite simple, economical, and the quality of such contacts is higher, since one of the components gives the material a high hardness, erosion resistance, a greater melting point, and the other increases the electrical conductivity.
Good results are obtained by applying copper-powered copper or silver for the manufacture of nozzle liners of solid fuel engines. Increasing such properties of impregnated tungsten, as thermal conductivity and electrical conductivity, the thermal expansion coefficient, significantly increases the durability of the engine. In addition, the evaporation of the impregnating metal from tungsten during the engine operation is positive, reducing heat flows and reducing the erosion effect of combustion products.
Tungsten powder is used in the manufacture of porous materials for the parts of the electrostatic ion engine. The use of tungsten for these purposes allows you to improve its main characteristics.
The heat and erosion properties of the nozzles made from tungsten, hardened by dispersed oxides ZrO2, MgO2, V2O3, HFO 2, increase compared to the nozzles from the sintered tungsten. After the appropriate preparation on the surface of the tungsten to reduce high-temperature corrosion, galvanic coatings are applied, for example, a nickel coating, which is performed in an electrolyte containing 300 g / l sulphid sodium, 37.5 g / l of boric acid at a current density of 0.5-11 A / DM 2, temperature 65 ° C and pH \u003d 4.
The content of the article
TUNGSTEN- (Wolframium), W is the chemical element 6 (VIB) of the group of the periodic system D.I. Iveleeva, atomic number 74, atomic weight 183.85. 33 Wolframa isotope is known: from 158 W to 190 W. In nature, five isotopes were found, three of which are stable: 180 W (share among natural isotopes 0.120%), 182 W (26.498%), 186 W (28,426%), and Other two weakly radioactive: 183 w (14.314%, T ½ \u003d 1.1 · 10 17 years), 184 W (30.642%, T ½ \u003d 3 · 10 17 years). Electronic shell configuration - 4F 14 5D 4 6S 2. The most characteristic degree of oxidation is +6. There are connections with the degrees of oxidation of tungsten +5, +4, +3, +2 and 0.
Back in 14-16 centuries. Miners and metallurgists in the ore mountains of Saxony noted that some ores violated the process of restoring tin stone (Cassiiterite mineral, SNO 2) and led to the globe of the molten metal. In the professional language of that time, this process was characterized as follows: "These ores are torn to the tin and devour him, like a wolf devour the sheep." Rudokops gave this "annoying" breed of the name "Wolfert" and "Wolfrahm", which means "Wolf Pena" or "Foam in a grazing wolf". German chemist and metallurgist George Agrikola in its fundamental labor Twelve books about metals (1556) leads the Latin name of this mineral - Spuma Lupi, or Lupus Spuma, which is essentially a tracker with a national German name.
In 1779 Peter Wulf (Peter Wulf) explored the mineral, now called tungsten (FEWO 4 · x.Mnwo 4), and concluded that he must contain an unknown substance. In 1783 in Spain, Brothers D "Elguyar (Juan Jose and Fausto D" Elhuyar de Suvisa) with the help of nitric acid was isolated from this acid ground mineral - yellow precipitate of an unknown metal oxide, soluble in ammonia water. In the mineral, iron and manganese oxides were also discovered. Juan and Fausto rolled the "Earth" with charcoal and received the metal, which they suggested calling "tungsten", and the mineral himself is "tungsten." Thus, the Spanish chemists of D "Eldgueir are the first to publish information about the discovery of the new element.
Later it became known that for the first time the tungsten oxide was discovered not in the "Earror of Olov" - tungsten, and in another mineral.
In 1758 Swedish chemist and mineralog Axel Fredrik Cronstedt opened and described an extraordinarily heavy mineral (Cawo 4, named after Sheelit), who called Tung Sen, which in Swedish means "heavy stone". The crocknedt was convinced that this mineral contains a new, not yet open, element.
In 1781, the Great Swedish Chemist Karl Shelele laid out the "heavy stone" nitric acid, at the same time, in addition to the calcium salt, the "yellow earth", which is not similar to the White Molybdenum Earth, first allocated for it three years ago. Interestingly, one of the brothers D "Elguyar worked at that time in his laboratory. Shelele called the metal" Tungsten ", by the name of the mineral, from which yellow oxide was first isolated. So the same element appeared two names.
In 1821, the background Leonard suggested calling the mineral Cawo 4 Scheelite.
Tungsten name can be found in Lomonosov; Solovyov and Gess (1824) call his wolf, Dvigubsky (1824) - tungsten.
Even at the beginning of the 20th century. In France, Italy and Anglo-Saxon countries, the element "Tungsten" was denoted as TU (from Tungsten). Only in the middle of the last century, a modern symbol of W is approved.
Tungsten in nature. Types of deposits.
Tungsten is a rather rare element, its Clark (percentage in the earth's crust) is 1.3 · 10 -4% (57th place among chemical elements).
Tungsten occurs mainly in the form of tungsten iron and manganese or calcium, and sometimes lead, copper, thorium and rare-earth elements.
The most common Wolframite mineral is a solid solution of iron and manganese (Fe, Mn) WO 4 solid solution. These are heavy solid color crystals from brown to black, depending on which element prevails in their composition. If more manganese (Mn: Fe\u003e 4: 1), then black crystals, if iron prevails (Fe: Mn\u003e 4: 1) - brown. The first mineral is called Gubneritis, the second - Ferberit. Wolframite paramagnetic and well conducts electric current.
From other tungsten minerals, industrial significance has a shelit - CAWO 4 tungsten. It forms brilliant, like glass, crystals of light yellow, sometimes almost white. Sheelit does not make a magnetic, but has another characteristic feature - the ability to luminescence. If it is illuminated by ultraviolet rays, it fluoresits in the dark with bright blue. The mixture of molybdenum changes the color of the glow of Sheelita: it becomes a pale blue, and sometimes even creamy. This property of Sheelita, used in geological intelligence, serves as a search sign, allowing to detect the deposits of the mineral.
As a rule, the field of tungsten ores are associated with the areas of propagation of granites. Large crystals of tungsten or Sheelita are rare. Typically, minerals are only integrated into ancient granite rocks. The average concentration of tungsten in them is only 1-2%, so it is quite difficult to extract it. A total of about 15 tungsten minerals are known. There are also galcite among them, which are two different crystalline modifications of PBWO 4 lead tungsten. Other minerals are products of decomposition or secondary forms of ordinary minerals - tungsten and Sheelita, for example, tungsten ocher and hydrotuncing, which is hydrated tungsten oxide formed from tungsten; Rolls - mineral containing bismuth and tungsten oxides. The only non-oxygen millal of tungsten - WS 2 Tungstenitis, the main reserves of which are focused in the United States. Typically, the content of tungsten in the deposited fields lies in the range from 0.3 to 1.0% WO 3.
All tungsten fields have a magmatic or hydrothermal origin. In the process of cooling the magma, differential crystallization occurs, so the sheelite and tungsten are often detected in the form of live, where the magma penetrated into cracks earth crust. Most of the tungsten fields are concentrated in young mountain chains - Alps, Himalayas and the Pacific. According to the American geological service for 2003 (U.S. Geological Surveys) in China there is about 62% of the world's collar reserves. Significant deposits of this element are also divorced in the USA (California, Colorado), Canada, Russia, South Korea, Bolivia, Brazil, Australia and Portugal.
World stocks of tungsten ores are estimated at 2.9 · 106 tons in terms of metal. China (1.8 · 106 tons) possesses the greatest stocks, the second place is divided by Canada and Russia (2.6 × 105 and 2.5 · 105 tons, respectively). In third place are the United States (1.4 · 105 tons), but now almost all American deposits are canned. Among the rest of the countries, Portugal (reserves of 25,000 tons) possess weighty stocks North Korea (35,000 tons), Bolivia (53,000 tons) and Austria (10,000 tons).
The annual global production of tungsten ores is 5.95 · 10 4 tons in terms of metal, of which 49.5 · 10 4 tons (83%) are extracted in China. 3,000 tons are produced in Russia, 3,000 tons in Canada.
On King Island in Australia, 2000-2400 tons of tungsten ore per year is mined. In Austria, Sheelit is mined in the Alps (Province of Salzburg and Shteierark). In Northeast Brazil, a joint field of tungsten, gold and bismuth (Caunung mine and the Calzas mine in Yukon) are being developed with an alleged margin of gold of 1 million ounces and 30,000 tons of tungsten oxide. The world leader in the development of tungsten raw materials is China (deposits of Zhianishi (60% of Chinese production of tungsten), Hongan (20%), UNNAN (8%), Guangjondon (6%), Guanji and Inner Mongolia (2% each) and others). The volumes of annual production in Portugal (Panashira deposit) are estimated at 720 tons of tolfram per year. In Russia, the main fields of tungsten ores are located in two regions: Far East (Lermontovskoye deposit, 1700 tons of concentrate per year) and in the North Caucasus (Kabardino-Balkaria, Tyrnyauz). The plant in Nalchik processes the ore to the tungsten oxide and the ammonium paraframat.
The largest consumer tungsten is Western Europe - Her share in the global market is 30%. 25% of total consumption falls on North America and China, and 12-13% of Japan. The demand for tungsten in the CIS countries is estimated at 3000 tons of metal per year.
More than half (58%) of the entire metal consumed is used in the production of tungsten carbide, almost a quarter (23%) - in the form of various alloys and steels. For the manufacture of tungsten "rolled products" (threads for incandescent lamps, electrical contacts, etc.) accounts for 8% of the tungsten produced, and the remaining 9% are used in obtaining pigments and catalysts.
Recycling tungsten raw materials.
Primary ore contains about 0.5% tungsten oxide. After flotation and separation of non-magnetic components, a breed remains containing about 70% WO 3. Then enriched ore (and oxidized tungsten scrap) is leached using carbonate or sodium hydroxide:
4FEWO 4 + O 2 + 4NA 2 CO 3 \u003d 4NAWO 4 + 2FE 2 O 3 + 4CO 2
6mnWO 4 + O 2 + 6NA 2 CO 3 \u003d 6NA 2 WO 4 + 2mn 3 O 4 + 6CO 2
WO 3 + Na 2 CO 3 \u003d Na 2 WO 4 + CO 2
WO 3 + 2NAOH \u003d Na 2 WO 4 + H 2 O
Na 2 WO 4 + CaCl 2 \u003d 2NACL + CAWO 4 ї.
The resulting solution is exempt from mechanical impurities, and then recycled. Calcium tungstenate is initially deposited, followed by its decomposition with hydrochloric acid and dissolving the WO 3 formed in aqueous ammonia. Sometimes cleaning the primary tungsten sodium is carried out with the help of ion exchange resins. The final product of the process - ammonium paraframat:
CAWO 4 + 2HCl \u003d H 2 WO 4 ї + CaCl 2
H 2 WO 4 \u003d WO 3 + H 2 O
WO 3 + 2NH 3 · H 2 O (conc.) \u003d (NH 4) 2 WO 4 + H 2 O
12 (NH 4) 2 WO 4 + 14HCl (Och.) \u003d (NH 4) 10 H 2 W 12 O 42 + 14NH 4 CL + 6H 2 O
Another method of isolating the tungsten from enriched ore is the processing of chlorine or chloride. This method is based on a relatively low boiling point of chloride and tungsten oxochlorides (300 ° C). The method is used to obtain a particularly pure tungsten.
The tungsten concentrate can be fused directly with coal or coke in a chamber with an electric arc. In this case, ferrololphram is obtained, which is used in the manufacture of alloys in the steel industry. The pure concentrate of Sheelita can also be added to the melt of steel.
About 30% of world consumption of tungsten is provided by recycling secondary raw materials. The polluted scrap of tungsten carbide, chips, sawdust and residues of powder tungsten are oxidized and ammonium is transferred to the ammonium paralolphramate. Scrap of high-sighted steels is disposed of in the production of these same steels (up to 60-70% of the entire melt). Volframa scrap of incandescent lamps, electrodes and chemical reagents is practically not processed.
The main intermediate product in the production of tungsten is the ammonium paravolframate (NH 4) 10 W 12 O 41 · 5H 2 O. It is the main transported tungsten compound. The calcination of ammonium paravolframate is obtained by tungsten oxide (VI), which is then treated with hydrogen at 700-1000 ° C and a metal tungsten powder is obtained. His sintering with carbon powder at 900-2200 ° C (cement process) is obtained by tungsten carbide.
In 2002, the price of ammonium paralolframate is the main commercial connection of tungsten - accounted for about $ 9,000 per ton in terms of metal. IN lately There was a tendency to reduce prices for tungsten products due to a large proposal from China and the countries of the former USSR.
In Russia, tungsten products produce: Skopinsky hydrometallurgical plant "Metallurg" ( Ryazan Oblast, Tungsten Concentrate and Anhydride), Vladikavkaz Plant "Win" (North Ossetia, Tungsten Powder and Bulls), Nalchik Hydrometellurgical Plant (Kabardino-Balkaria, Metal Tungsten, Tungsten Carbide), Kirovgrad Solid Alloy Carbide (Sverdlovsk Region, Tungsten Carbide, Wolframe Powder ), Elektrostal (Moscow region, Paraolframat Ammonium, Tolframa carbide), Chelyabinsk Electrometallurgical Plant (Ferrovolfram).
Properties of a simple substance.
Metal tungsten has a light gray color. After carbon, he has the highest melting point among all simple substances. Its value is determined in the range of 3387-3422 ° C. At tungsten - excellent mechanical qualities at high temperatures and the smallest expansion coefficient among all metals. Boiling point 5400-5700 ° C. Wolfram is one of the most heavy metals with a density of 19250 kg / m 3. Volframa electrical conductivity at 0 ° C - the value of about 28% of the electrical conductivity of silver, which is the most electrically conductive metal. Pure tungsten is fairly easy to process, but it usually contains carbon and oxygen impurities, which gives the metal known to all the hardness.
Wolfram has a very high stretching and compression module, a very high resistance of the temperature creep, high heat and electrical conductivity, a high coefficient of electron emission, which can still be improved by the fusion of tungsten with some oxides of metals.
Tungsten chemically racks. Salt, sulfuric, nitrogen, fluoride hydrochloric acid, royal vodka, aqueous sodium hydroxide solution, ammonia (up to 700 ° C), mercury and mercury pairs, air and oxygen (up to 400 ° C), water, hydrogen, nitrogen, carbon monoxide (up to 800 ° C), chloride (up to 600 ° C) on tungsten do not work. Ammonia react with a tungsten ammonia in a mixture with hydrogen peroxide, liquid and boiling sulfur, chlorine (over 250 ° C), hydrogen sulfide under the conditions of red caginee, hot tsarist vodka, a mixture of hydrothestheaster and nitric acids, nitrate melts, nitrite, potassium chlorate, lead dioxide , sodium nitrite, hot nitric acid, fluorine, bromine, iodine. Tungsten carbide is formed when carbon interacts with tungsten at temperatures above 1400 ° C, oxide - when interacting with water vapor and sulfur dioxide (at a red dip), carbon dioxide (above 1200 ° C), aluminum, magnesium and thorium oxides.
Properties of essential tungsten compounds.
Among the most important tungsten compounds are its oxide, chloride, carbide and ammonium paralolphramate.
Tungsten Oxide (VI) WO 3 is a light yellow crystalline substance, when heated becomes orange, melting point 1473 ° C, boiling - 1800 ° C. The corresponding tungsten acid is unstable, in aqueous solution The precipitate drops dihydrate, losing one water molecule at 70-100 ° C, and the second - at 180-350 ° C. When WO 3 reaction, tungstenates are formed with alkalis.
Anions of tungsten acids are prone to the formation of polisogencies. When reactions with concentrated acids, mixed anhydrides are formed:
12WO 3 + H 3 PO 4 (kip., Conc.) \u003d H 3
In the interaction of tungsten oxide with metallic sodium, nonstociometric sodium tungsten is formed, the name "Tungsten Bronze" is formed:
WO 3 +. x.Na \u003d Na. x. WO 3.
In the restoration of tungsten oxide with hydrogen at the time of release, hydrated oxides with a mixed degree of oxidation are formed - "Tungsten Blue" WO 3- n. (OH) n. , n. \u003d 0.5-0.1.
WO 3 + Zn + HCl ® ("Xin"), W 2 O 5 (OH) (brown.)
Tungsten Oxide (VI) Semiproduct in the production of tungsten and its connections. It is a component of some industrially important hydrogenation catalysts and pigments for ceramics.
Higher Tungsten chloride WCL 6 is formed in the interaction of tungsten oxide (or metal tungsten) with chlorine (as well as with fluorine) or carbon tetrachloride. It differs from other tungsten compounds of low boiling point (347 ° C). According to chemical nature Chloride is a tungsten acid chloride, so incomplete chloranhydrides are formed when interacting with water, when interacting with alkalis - salts. As a result of the recovery of tungsten chloride by aluminum in the presence of carbon monoxide, tungsten carbonyl is formed:
WCL 6 + 2AL + 6CO \u003d ї + 2AlCl 3 (on the air)
WC tungsten carbide is obtained by reacting powder tungsten with coal in the reducing atmosphere. The hardness, comparable with the diamond, determines the scope of its application.
Ammonium tungsten (NH 4) 2 WO 4 is stable only in ammonium solution. In dilute hydrochloric acid The ammonium (NH 4) 10 H 2 W 12 O 42 (NH 4) 10 H 2 W 12 O 42, which is the main semi-product of tungsten in the global market falls into the precipitate. Ammonium paralolframate is easily decomposed when heated:
(NH 4) 10 H 2 W 12 O 42 \u003d 10NH 3 + 12WO 3 + 6H 2 O (400 - 500 ° C)
The use of tungsten.
The use of pure metal and tungsten-containing alloys is based mainly on their refractory, hardness and chemical resistance. Pure tungsten used for the manufacture of filaments of electric lamps of incandescent and electron-ray tubes, in the production of crucibles for evaporation of metals, in the contacts of automotive ignition distributors, in the targets of X-ray tubes; As windings and heating elements of electric furnaces and as a design material for cosmic and other devices operated at high temperatures. Film steel (17.5-18.5% tungsten), stelite (based on cobalt with the addition of CR, W, C), hastalian (Ni-based stainless steel) and many other alloys contain tungsten. The basis for the production of instrumental and heat-resistant alloys is ferrololphram (68-86% W, up to 7% Mo and iron), which is easily obtained by direct reduction of tungsten or shellite concentrates. "Win" is a very solid alloy containing 80-87% tungsten, 6-15% cobalt, 5-7% of carbon, irreplaceable in the processing of metals, in the mountain and oil industry.
Calcium and magnesium tungsten are widely used in fluorescent devices, other tungsten salts are used in the chemical and tanning industry. Tungsten Disulfide is a dry high-temperature lubricant, a stable up to 500 ° C. Wolfram bronze and other element connections are used in the manufacture of paints. Many tungsten compounds are excellent catalysts.
For many years, from the moment of opening, tungsten remained laboratory rarity, only in 1847 Oxland received a patent for the production of sodium tungsten, tungstenic acid and tungsten from cassiterite (tin stone). The second patent obtained by Oxland in 1857 described the production of iron-tungsten alloys, which constitute the basis of modern high-speed steels.
In the middle of the 19th century The first attempts were made to use tungsten in the production of steel, but for a long time I could not implement these developments in the industry due to the high price of metal. The increased need for alloyed and high-strength steel has led to the launch of the production of high-speed steels at the company "Bethlehem Steel" (Bethlehem Steel). Samples of these alloys were first represented in 1900 at the World Exhibition in Paris.
Technology manufacturing tungsten threads and its history.
Production volumes of tungsten wire have a small proportion among all branches of tungsten use, but the development of technology for its receipt has played a key role in the development of powder metallurgy of refractory compounds.
From 1878, when Svon demonstrated in Newcastle invented by it eight and sixteen-centurous coal lamps, it was a search for a more suitable material for the manufacture of incandescent threads. The first coal lamp had the effectiveness of only 1 lumen / watt, which was increased in the next 20 years modification of coal processing methods in two and a half times. By 1898, the light statement of such light bulbs was 3 lumens / watts. Coal threads in those times were heated by passing the electric current in the atmosphere of heavy hydrocarbon vapors. With the porolysis of the latter, the resulting carbon filled the pores and irregularity of the thread, giving it a bright metal glitter.
At the end of the 19th century Velsbach background for the first time made a metal thread for incandescent bulbs. He made it from Osmia (T pl \u003d 2700 ° C). Osmisy threads have an effectiveness of 6 lumens / watts, however, the osmium is a rare and extremely expensive element of the platinum group, therefore there was no wide use in the manufacture of household devices. Tantalum with a melting point of 2996 ° C was widely used in the form of an elongated wire from 1903 to 1911 due to the works of Bolton von Siemens and Chalkk. The effectiveness of tantalum lamps was 7 lumens / watts.
Tungsten began to be used in incandescent lamps in 1904 and displaced all other metals to 1911 in this capacity. The usual incandescent lamp with tungsten thread has a lumen 12 lumen / watt, and high-voltage lamps are 22 lumens / watts. Modern fluorescent lamps with tungsten cathode have the effectiveness of about 50 lumens / watts.
In 1904, at Siemens-Halsk, they tried to apply the process of wire dragging for more refractory metals, such as tungsten and thorium. The rigidity and lack of tungsten tungsten did not allow a smooth process. However, later, in 1913-1914, it was shown that melted tungsten can be rolled and stretched using a partial recovery procedure. The electric arc was passed between a tungsten rod and partially molten tungsten droplet placed in a graphite crucible, coated from inside tungsten powder and in atmosphere of hydrogen. Thus, small drops of molten tungsten were obtained, about 10 mm in diameter and 20-30 mm in length. Although with difficulty, but you could already work with them.
In the same years, Yust and Hannaman patented the process of manufacturing tungsten threads. The thin metal powder was mixed with the organic binder, the resulting paste was passed through the filters and heated in a special atmosphere to remove the binder, and the fine thread of pure tungsten was obtained.
In 1906-1907, a well-known extrusion process was developed, used before the early 1910s. The black tungsten powder of a very thin grinding was mixed with dextrin or starch before the formation of a plastic mass. With hydraulic pressure, this mass is melted through thin diamond sieves. The thread thus obtained turned out to be sufficiently strong in order to be wound on the coil and dried. Next, the threads were cut on "studs", which were heated in an atmosphere of inert gas to the temperature of red kayage to remove moisture residues and light hydrocarbons. Each "hairpin" was fixed in the clamp and heated in the atmosphere of hydrogen to a bright glow by passing the electric current. This led to the final removal of unwanted impurities. At high temperatures, individual tungsten particles are splashing and form a homogeneous solid metal thread. These threads are elastic, although fragile.
At the beginning of the 20th century Yust and Hannaman developed another process that is characterized by its originality. The coal thread with a diameter of 0.02 mm was covered with tungsten by incandescent in the atmosphere of hydrogen and vapors of tungsten hexachloride. The thread coated thus heated to a bright glow in hydrogen under reduced pressure. At the same time, the tungsten sheath and carbon core completely melted with each other, forming tungsten carbide. The resulting thread was white and was fragile. Next, the thread was heated in a stream of hydrogen, which interacts with carbon, leaving a compact thread of pure tungsten. The threads possessed the same characteristics as the extrusion obtained in the process.
In 1909, the American Kulija managed to get a macked tungsten without the use of fillers, but only with the help of reasonable temperature and machining. The main problem in obtaining tungsten wire was to the rapid oxidation of tungsten at high temperatures and the presence of a grainy structure in the resulting tungsten, which led to its fragility.
Modern production of tungsten wire is a complex and accurate technological process. The feedstock serves powder tungsten, obtained by the recovery of ammonium paravolframate.
Wolframe powder used for the production of wire must have a high purity. Usually mix tungsten powders of various origins to averaged the quality of the metal. They are mixed in the mills and to avoid oxidation of the metal heated by friction in the chamber skip the stream of nitrogen. Then the powder is pressed in steel molds on hydraulic or pneumatic presses (5-25 kg / mm 2). In the case of using contaminated powders, the press is obtained by fragile, and a fully oxidized organic binder is added to eliminate this effect. At the next stage, there is a preliminary sintering of the headacs. When heating and cooling the press in the stream of hydrogen, their mechanical properties are improved. Presses still remain fragile enough, and their density is 60-70% of the tungsten density, so the headacters are subjected to high-temperature sintering. The headaccus is clamped between the contacts cooled by water, and in the atmosphere of dry hydrogen, the current is passed through it to heating it almost to the melting point. Due to the heating, tungsten sinters and its density increases to 85-95% of the crystalline, while the grains are increasing, tungsten crystals grow. Then the forging with high (1200-1500 ° C) temperature. In the special apparatus, the headacters are passed through the chamber, which is squeezed with a hammer. For one transmission, the diameter of the headacter decreases by 12%. When forging, tungsten crystals are lengthened, a fibrillar structure is created. After the forging, the wire broach. The rods are lubricated and skipped through sieves from diamond or tungsten carbide. The degree of exhaust depends on the purpose of the obtained products. The diameter of the obtained wire is about 13 microns.
Biological role of tungsten
limited. His neighbor in the Molybdenum group is indispensable in enzymes that ensure the binding of atmospheric nitrogen. Previously, tungsten was used in biochemical studies only as molybdenia antagonist, i.e. Replacing molybdenum on tungsten in the active center of the enzyme led to its deactivation. The enzymes, on the contrary, deactivating when replacing tungsten on molybdenum, found in thermophilic microorganisms. Among them formate dehydrogenases, aldehyde-ferredoxin-oxidoreductase; Formaldehyde-ferred-xin-oxidoreductase; acetylenehydrate; Reduccataz carboxylic acid. The structures of some of these enzymes, for example, Aldehyde-ferredoxin-oxidoreductase are now defined.
The severe consequences of the effects of tungsten and its compounds per person are not identified. With long-term exposure of large doses of tungsten dust, pneumoconiosis may occur, the disease caused by all heavy powders falling into the lungs. The most frequent symptoms of this syndrome - cough, respiratory disorders, atopic asthma, changes in the lungs, whose manifestation decreases after the cessation of contact with the metal.
Internet materials: http://miners.usgs.gov/miners/pubs/commodity/tungsten/
Yuri Krutyakov
Literature:
Colin J. Smitelles TungstenM., Metallurgizdat, 1958
Agte K., Witzek I. Tungsten and Molybdenum, M., Energy, 1964
Figurovsky N.A. The opening of the elements and the origin of them is callediy. M., Science, 1970
Popular Library of Chemical Elements. M., Science, 1983
US Geological Survey Minerals Yearbook 2002
Lviv N.P., Kraist A.N., Antipov A.N. Tungsten-containing enzymes, vol. 6, 7. Biochemistry, 2002
Tungsten - metal with unique properties. It has the highest boiling point (5555 ° C - the same temperature in the photoosphere of the Sun) and melting (3422 ° C) among metals, while the lowest thermal expansion coefficient.
In addition, it is one of the highest, heavy, stable and dense metals: tungsten density is comparable with density and uranium and 1, 7 times higher than lead.
Its electrical conductivity is almost 3 times lower than that of copper, but quite high. In purified form, tungsten - silver-white, resembles steel or platinum in appearance, with significant heating - up to 1600 ° C - perfectly goes.
Opening and Application History
Metal received its name from tungsten - mineral, whose name from Latin is translated as "wolf foam", and from German - like "Wolf Cream". Such a strange name is associated with the behavior of the mineral: he interpreted to pay tin when he was accompanied by the mined ore, turning the material in the middle ages in the slag foam. The then said about him: "Eats tin, like a wolf sheep."
The opening of pure tungsten occurred in two places at the same time. In 1781, Chemik Sherle (Sweden) receives a "heavy stone", affecting nitric acid on the shelit. And in 1783, the Elir Chemists (Spain) also report the allocation of pure tungsten. 
The main reserves of the metal were in Kazakhstan, Canada, China, USA.
The use of tungsten. Wolfram carbide.
Approximately 50% tungsten used to produce solid materials, in particular - tungsten carbide with a melting point of 2770 ° C.
Tungsten carbide - chemical compound equal in the number of tungsten and carbon atoms. It is 2 times hard than steel, has a stiffness coefficient 9 on the Moos scale (coefficient 10).
Tungsten carbide is used for manufacture:
- cutting tools, extremely resistant to abrasion and exposure to high temperatures;
- armor-piercing ammunition;
- tank armor; 
- parts of airplanes and engines;
- details spacecraft and missiles;
- equipment for the nuclear industry;
- ballasts, commercial aircraft, racing cars;
- surgical instruments intended for open (strip) surgery and laparoscopic (scissors, tweezers, grippers, cutters and others) - they are more expensive than medical steel, but have better performance;
- jewelry, especially wedding rings: the popularity of tungsten in engagement rings is caused physical properties Metal (durability, refractory, as if symbolizing the same strength of relationships) and its appearance - polished, tungsten remains indefinitely a shorter, mirror appearance, since it is impossible to scratch it in everyday life;
- balls in expensive ballpoint handles;
- Calibration blocks used, in turn, for the production of precision lengths in the size of metrology.
Other cases of tungsten use
Tungsten are used in the production of heating elements for high-temperature vacuum furnaces, incandescent threads in a variety of lighting devices. 
Tungsten Sulfide found an application as high-temperature lubricant, withstanding heating to 500 ° C. Wolframatov single crystals are used in nuclear physics and medicine.
One of the most common chemical elements is tungsten. It is indicated by the symbol W and has a nuclear number - 74. Tungsten refers to a group of metals having high resistance to wear and melting point. In the periodic Mendeleev system, it is in the 6th group, has similar properties with "neighbors" - molybdenum, chrome.
Opening and History
Back in the XVI century, such a mineral was known as tungsten. He was interesting because when smelting tin from ore, his foam turned into a slag and, of course, it hurt the production. Since then, tungsten began to call the "Wolf Pen" (with it. Wolf Rahm). The name of the mineral passed onto the metal itself.
Swedish chemist in 1781 processed with nitric acid Metal Sheelit. In the process of experiment, it turned out the yellow heavy stone - Tungsten Oxide (VI). Two years later, the brothers EloR (Spanish chemists) received from the Saxon mineral to tungsten in its pure form.
It is mined this element and its ores in Portugal, Bolivia, South Korea, Russia, Uzbekistan, and the greatest reserves were found in Canada, the United States, Kazakhstan and China. A total of 50 tons of this element are mined per year, so it costs expensive. Consider in more detail that for metal tungsten.
Properties of element
As mentioned earlier, tungsten is one of the most refractory metals. It has a shiny light gray color. Its melting point is 3422 ° C, and boiling - 5555 ° C, density in pure form - 19.25 g / cm 3, and a hardness of 488 kg / mm². This is one of the heaviest metals with high corrosion resistance. It is practically not soluble in sulfur, hydrochloric and hydrofluoric acids, but quickly reacts with hydrogen peroxide. What kind of metal tungsten, if it does not react with molten alkalis? When reacting with sodium hydroxide and oxygen, it forms two compounds - sodium tungsten and conventional water N 2 O. It is interesting that when the temperature is raised, tungsten self-dishes it, then the process is much more active.
Getting tungsten
On the question of which group of metals are tungsten, it is possible to answer that it is included in the category of rare elements, like Rubidium and Molybdenum. And this, in turn, means that it is characterized by a small scale of production. In addition, such a metal is not obtained by recovery from raw materials, first it is processed on chemical compounds. How is the receipt of rare metal?
- From the ore material, the necessary element is isolated and concentrated in solution or precipitate.
- The next step is obtained by a pure chemical connection by cleaning.
- From the resulting substance, pure rare metal - tungsten.
To enrich ores, gravity, flotation, magnetic or electrostatic separation are used. As a result, a concentrate is obtained, which contains 55-65% WO 3 anhydride. It is restored to obtain a powder with hydrogen or carbon. For some products, this process of obtaining an element ends. So, tungsten powder is used to prepare solid alloys.
Manufacture of headaccles
We have already found out that for metal tungsten, and now we will find out what kind of zoom is manufactured. Compact ingots are made of powder compounds - headaccations. For this, only powder is used, which has been restored by hydrogen. They are manufactured by pressing and sintering. It turns out quite durable, but fragile bars. In other words, they are poorly forging. To improve this technological property, the headacters are subjected to high temperature processing. From this product make another sorting.
Tungsten rods
Of course, this is one of the most common types of products from this metal. What kind of tungsten is used for making them? These are the above-described headaccles that are subjected to forging on a rotary forging machine. It is important to note that the process occurs in the heated state (1450-1500 ° C). The obtained rods are used in a wide variety of industries. For example, for the manufacture of welding electrodes. In addition, tungsten rods were widely used in heaters. They work in furnaces at temperatures up to 3000 ° C in vacuo, inert gas or hydrogen. The rods can also be used as cathodes of electronic and gas-discharge devices, radiolmp.
Interestingly, the electrodes themselves are uncomplicated, and therefore during welding, a feeding material is required (wire, rod). When melting with a weldable material, it creates a welding bath. These electrodes are usually used for welding non-ferrous metals.
Tungsten and wire
Here is another type of widespread products. Tungsten wire is made from forged rods discussed by us earlier. Fitting is made with a gradual decrease in temperature from 1000 ° C to 400 ° C. Then the product is purified by annealing, electrolytic polishing or electrolytic etching. Since tungsten - refractory metal, wire is used in resistance elements in heating ovens at temperatures up to 3000 ° C. The thermoelectric transducers are made of it, as well as the spiral of incandescent lamps, loop heaters and much more.
Tungsten compounds with carbon
Tungsten carbides are considered very important from a practical point of view. They are used for the manufacture of solid alloys. Compounds with carbon have a positive electrical resistivity coefficient and good metal conductivity. Tungsten carbides are formed by two types: WC and W 2 C. They differ in their behaviors in acids, as well as solubility in other compounds with carbon.
Based on tungsten carbides, two types of solid alloys are manufactured: sintered and cast. The latter are obtained from a powdered compound and carbide with a disadvantage of (less than 3%) by casting. The second type is made from WC Tungsten Monocarbide and cementing metal-bundles, which can be nickel or cobalt. Sintered alloys are obtained only by powder metallurgy. The powder of cementing metal and tungsten carbide is mixed, pressed and sin. Such alloys have high strength, hardness of wear resistance.
In the modern metallurgical industry, they are used to process metal cutting and for the manufacture of drilling instruments. One of the most common alloys are VK6 and VK8. They are used for the manufacture of cutters, cutters, drills and other cutting tools.
The scope of tungsten carbides is sufficiently volumetric. So, they are used for manufacture:
- armor-piercing supplies;
- parts of engines, airplanes, spacecraft and missiles;
- equipment in the nuclear industry;
- surgical instruments.
In the West, tungsten carbides in jewelry, especially for the manufacture of wedding rings, are particularly widely used. Metal looks beautiful, aesthetically, it is easy to handle it.
This is explained by the fact that they are incredibly wear-resistant. To scratch such a product, you have to make a lot of effort. Even in a few years, the ring will look like new. It does not hide, the relief pattern will damage, and the polished part will not lose its gloss.
Tungsten and rhenium
The alloy of these two elements is quite widely used for the manufacture of high-temperature thermocouples. Wolfram - what metal? Like rhenium, it is a heat-resistant metal, and the doping of elements reduces this property. But what if you take two almost the same substances? Then the temperature of their melting will not decrease.
If you use rhenium as a additive, an increase in heat resistance and plasticity of tungsten will be observed. This alloy is obtained by smelting in powder metallurgy. Thermocouples manufactured from these materials are heat-resistant and can measure the temperature greater than 2000 ° C, but only in an inert medium. Of course, such products are expensive, because in one year there are only 40 tons of rhenium and only 51 ton of tungsten.
Tungsten. Chemical element, symbolW (lat. Wolframium, English. Tungsten, Franz. Tungstene, it. Wolfram, from him. Wolf Rahm - wolf saliva, foam). It has a sequence number74, atomic weight 183, 85, density 19, 30 g / cm 3, melting temperature3380 ° C, boiling point5680 ° C.
Tungsten - metal light gray, at room temperature has a high corrosion resistance in water and in air, as well as in acids and alkalis. It begins to oxidize a little in air when400-500 ° C (at a red casting temperature) and intensively oxidized at higher temperatures. Tungsten forms two stable oxides:WO 3 and WO 2 . With hydrogen, tungsten does not interact in almost the melting itself, and with nitrogen begins to enter into the reaction only at temperatures more2000 ° S. with chlorine tungsten forms chloridesWCL 2, WCl 4, WCl 5, WCl 6. Solid carbon and some gases containing it1100-1200 ° C react with tungsten, forming carbidesWC and W 2 C.
Tungsten dissolves in the mixtures of the smelting andnitric acids Also dissolved in molten alkalis when accessing air and especially oxidizing agents. Separate acids on tungsten are not valid.
Wolfram is very high purity plastic at room temperature. For strength at high temperatures, tungsten exceeds all other metals. On themechanical properties Wolframa is severely influenced by impurities. The content in the metal of small amounts of impurities makes it very fragile (cold). Most bad influence Oxygen, nitrogen, carbon, iron, phosphorus, silicon are applied to the properties of tungsten.
Tungsten are widely used in the radiolampic, radiotechnical and electron-vacuum industry for the manufacture of filaments of incandescent, heaters and screens of high-temperature vacuum furnaces, electrical contacts, x-ray cathodes.
In metallurgy, tungsten dop steel and used in the manufacture of solid alloys (for example, a metal-ceramic alloy based on tungsten carbide will win), in the chemical industry, paints and catalysts are made, in rocket techniques - products working at very high temperatures in the nuclear industry - Tigli for storing radioactive materials, because protective action at alloy tungsten,nickel and copper higher than lead . Metal alloys are obtained by sintering, and not pressure because at the melting point of tungsten, many metals are converted to steam.
Tungsten are also used to apply coatings: on parts operating at very high temperatures in reducing and neutral environments; on foundry forms frommolybdenum used to obtain rods strongly radioactive metals; On the details working for friction.
Also widespread alloys based on tungsten with rhenium. Adding (up20-25%) reduces tungsten transition temperature into a fragile state, dramatically increases its plastic at normal temperature and improves technological properties. Alloys are obtained by powder metallurgy and melting in electric arc vacuum furnaces. From these alloys produce thermocouples, electrical contacts.
Tungsten Alloys S.molybdenum suitable for working at temperatures3000 ° C, apply them for the nozzles of jet engines.
When heated tungsten above400 ° With on its surface, powdered oxide of yellow color is formed, which evaporates noticeably at temperatures800 ° C. Therefore, tungsten can be used as high-strength material at high temperatures only with the reliable protection of the surface of the product from the exposure of an oxidizing medium or when working in a neutral environment or in vacuo. For short-term protection of tungsten from oxidation with2000-3000 ° C is used ceramic enhaid coatings containing refractory compounds as the main aggregate to them a refractory binder glass.
