Tungsten is a dull silvery metal with the highest melting point of any pure metal.
Also known as Tungsten, from which the element takes its symbol, W, tungsten is more resistant to tearing than diamond and much harder than steel. It is the unique properties of refractory metals - its strength and ability to withstand high temperatures - that make it ideal for many commercial and industrial applications.
Tungsten is primarily extracted from two types of minerals: wolframite and scheelite. However, tungsten recycling also accounts for about 30% of global supply. China is the world's largest producer of the metal, providing more than 80% of the world's supply.
After processing and separating the tungsten ore, the chemical form, ammonium paratungstate (APT), is produced. APT can be heated with hydrogen to form tungsten oxide or reacted with carbon at temperatures above 1925 °F (1050 °C) to produce tungsten metal.
Applications:
The primary use of tungsten for over 100 years was as the filament of incandescent lamps. Made in small quantities of potassium aluminum silicate, tungsten powder is sintered at high temperatures to create the wire filament that is at the center of the light bulbs that light millions of homes around the world.
Thanks to tungsten's ability to retain its shape at high temperatures, tungsten filaments are now also used in a variety of household applications, including lamps, spotlights, heating elements in electric ovens, microwave ovens, X-ray tubes, and cathode ray tubes (CRTs) in computer monitors and televisions.
The metal's tolerance to intense heat also makes it ideal for thermocouples and electrical contacts in electric arc furnaces and welding equipment. Applications that require concentrated mass or weight, such as counterweights, fishing weights, and darts, often use tungsten due to its density.
Wolfram carbide:
Tungsten carbide is made by either combining one tungsten atom with one carbon atom (represented by the chemical symbol WC) or two tungsten atoms with one carbon atom (W2C). This is done by heating tungsten powder with carbon at temperatures ranging from 2550 °F to 2900 °F (1400 °C to 1600 °C) in a stream of hydrogen gas.
According to the Moh hardness scale (a measure of one material's ability to scratch another), tungsten carbide has a hardness of 9.5, only slightly lower than diamond. For this reason, this solid compound is sintered, a process that requires pressing and heating a powder mold at high temperatures to produce products used in machining and cutting. This results in materials that can operate under high temperature and stress conditions, such as drills, turning tools, cutters and armor-piercing ammunition.
Cemented carbide is produced using a combination of tungsten carbide and cobalt powder and is used to make wear-resistant tools such as those used in the mining industry.
The tunnel boring machine used to dig the canal tunnel linking the UK to Europe was actually fitted with almost 100 cemented carbide tips.
Tungsten alloys:
Tungsten metal can be combined with other metals to increase their strength and resistance to wear and corrosion. Steel alloys often contain tungsten for these beneficial properties. Many high-speed steels used in cutting and machining tools such as saw blades contain about 18 percent tungsten.
Tungsten steel alloys are also used in the production of rocket engine nozzles, which must have high heat-resistant properties. Other tungsten alloys include Stellite (cobalt, chromium and tungsten), which is used in bearings and pistons for its durability and wear resistance, and Hevimet, which is produced by sintering tungsten alloy powder and is used in ammunition, dart barrels, and golf clubs.
Superalloys of cobalt, iron or nickel, along with tungsten, can be used to make turbine blades for aircraft.
The content of the article
TUNGSTEN(Wolframium), W chemical element 6 (VIb) of the group of the periodic system of D.I. Mendeleev, atomic number 74, atomic mass 183.85. 33 isotopes of tungsten are known: from 158 W to 190 W. Five isotopes have been discovered in nature, three of which are stable: 180 W (share among natural isotopes 0.120%), 182 W (26.498%), 186 W (28.426%), and the other two are weakly radioactive: 183 W (14.314%, T ½ = 1.1 10 17 years), 184 W (30.642%, T ½ = 3 10 17 years). Electron shell configuration 4f 14 5d 4 6s 2. The most typical oxidation state is +6. Compounds with tungsten oxidation states +5, +4, +3, +2 and 0 are known.
Back in the 14th-16th centuries. miners and metallurgists in the Ore Mountains of Saxony noted that some ores interfered with the reduction process of tin stone (cassiterite mineral, SnO 2) and led to slagging of the molten metal. In the professional language of that time, this process was characterized as follows: “These ores tear out the tin and devour it, like a wolf devours a sheep.” The miners gave this “annoying” breed the names “Wolfert” and “Wolfrahm”, which translated means “wolf foam” or “foam in the mouth of an angry wolf.” German chemist and metallurgist Georg Agricola in his fundamental work Twelve books about metals(1556) gives the Latin name for this mineral, Spuma Lupi, or Lupus spuma, which is essentially a tracing of the German folk name.
In 1779, Peter Wulf explored the mineral now called wolframite (FeWO 4 x MnWO 4), and came to the conclusion that it must contain a previously unknown substance. In 1783 in Spain, the d'Elguyar brothers (Juan Jose and Fausto D'Elhuyar de Suvisa), using nitric acid, isolated from this mineral “acid earth” - a yellow precipitate of an oxide of an unknown metal, soluble in ammonia water. Oxides of iron and manganese were also found in the mineral. Juan and Fausto calcined the “earth” with charcoal and obtained a metal, which they proposed to call “tungsten”, and the mineral itself “wolframite”. Thus, the Spanish chemists d'Elguiar were the first to publish information about the discovery of a new element.
Later it became known that for the first time tungsten oxide was discovered not in the “tin eater” wolframite, but in another mineral.
In 1758, Swedish chemist and mineralogist Axel Fredrik Cronstedt discovered and described an unusually heavy mineral (CaWO 4 , later named scheelite), which he named Tung Sten, which means “heavy stone” in Swedish. Kronstedt was convinced that this mineral contained a new, not yet discovered, element.
In 1781, the great Swedish chemist Karl Scheele decomposed the “heavy stone” with nitric acid, discovering, in addition to the calcium salt, “yellow earth”, which was not similar to the white “molybdenum earth”, which he had first isolated three years earlier. It is interesting that one of the d'Elguiar brothers was working in his laboratory at that time. Scheele called the metal “tungsten”, after the name of the mineral from which yellow oxide was first isolated. Thus, two names appeared for the same element.
In 1821, von Leonhard proposed calling the mineral CaWO 4 scheelite.
The name tungsten can be found in Lomonosov; Soloviev and Hess (1824) call it thistle, Dvigubsky (1824) - tungsten.
Back at the beginning of the 20th century. in France, Italy and the Anglo-Saxon countries, the element “tungsten” was designated as Tu (from tungsten). It was only in the middle of the last century that the modern symbol W was established.
Tungsten in nature. Types of deposits.
Tungsten is a rather rare element, its clarke (percentage content in the earth's crust) is 1.3·10 4% (57th place among chemical elements).
Tungsten occurs primarily in the form of iron and manganese or calcium tungstates, and sometimes lead, copper, thorium and rare earth elements.
The most common mineral wolframite is a solid solution of iron and manganese tungstates (Fe, Mn)WO 4 . These are heavy, hard crystals ranging in color from brown to black, depending on which element predominates in their composition. If there is more manganese (Mn:Fe > 4:1), then the crystals are black, but if iron predominates (Fe:Mn > 4:1) they are brown. The first mineral is called hübnerite, the second - ferberite. Wolframite is paramagnetic and conducts electricity well.
Of other tungsten minerals, scheelite calcium tungstate CaWO 4 is of industrial importance. It forms shiny, glass-like crystals that are light yellow, sometimes almost white. Scheelite is not magnetic, but has another characteristic feature - the ability to luminesce. When illuminated with ultraviolet rays, it fluoresces bright blue in the dark. The admixture of molybdenum changes the color of the glow of scheelite: it becomes pale blue, and sometimes even cream. This property of scheelite, used in geological exploration, serves as a search feature to detect mineral deposits.
As a rule, deposits of tungsten ores are associated with areas of granite distribution. Large crystals of wolframite or scheelite are very rare. Usually minerals are only interspersed with ancient granite rocks. The average concentration of tungsten in them is only 12%, so it is quite difficult to extract it. In total, about 15 tungsten minerals are known. Among them are rasoite and stoltsite, which are two different crystalline modifications of lead tungstate PbWO 4 . Other minerals are decomposition products or secondary forms of the common minerals wolframite and scheelite, such as tungsten ocher and hydrotungstite, which is a hydrated tungsten oxide formed from wolframite; Rousselite is a mineral containing oxides of bismuth and tungsten. The only non-oxide tungsten mineral is tungstenite WS 2, the main reserves of which are concentrated in the USA. Typically, the tungsten content in developed deposits ranges from 0.3 to 1.0% WO 3 .
All tungsten deposits are of igneous or hydrothermal origin. As magma cools, differential crystallization occurs, which is why scheelite and wolframite are often found as veins where magma has penetrated cracks in the earth's crust. Most of the tungsten deposits are concentrated in young mountain ranges - the Alps, Himalayas and the Pacific belt. According to the 2003 U.S. Geological Surveys, China contains about 62% of the world's tungsten reserves. Significant deposits of this element have also been explored in the USA (California, Colorado), Canada, Russia, South Korea, Bolivia, Brazil, Australia and Portugal.
World reserves of tungsten ores are estimated at 2.9·106 tons in terms of metal. China has the largest reserves (1.8 106 tons), Canada and Russia share second place (2.6 105 and 2.5 105 tons, respectively). The United States is in third place (1.4·105 tons), but now almost all American deposits are mothballed. Among other countries, Portugal (reserves 25,000 tons), North Korea (35,000 tons), Bolivia (53,000 tons) and Austria (10,000 tons) have significant reserves.
The annual world 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. In Russia 3,400 tons are mined, in Canada 3,000 tons.
At King Island in Australia, 20002400 tons of tungsten ore are mined per year. In Austria, scheelite is mined in the Alps (the provinces of Salzburg and Steyermark). A joint tungsten-gold-bismuth mine is being developed in northeastern Brazil (the Kanung mines and the Calsas deposit in the Yukon) with an estimated gold reserve of 1 million ounces and 30,000 tons of tungsten oxide. The world leader in the development of tungsten raw materials is China (Jianshi deposits (60% of Chinese tungsten production), Hunan (20%), Yunnan (8%), Guandong (6%), Guanzhi and Inner Mongolia (2% each) and others). Annual production volumes in Portugal (Panaschira deposit) are estimated at 720 tons of tungsten per year. In Russia, the main deposits of tungsten ores are located in two regions: in the Far East (Lermontovskoye deposit, 1700 tons of concentrate per year) and in the North Caucasus (Kabardino-Balkaria, Tyrnyauz). The Nalchik plant processes ore into tungsten oxide and ammonium paratungstate.
The largest consumer of tungsten is Western Europe; its share of the world market is 30%. North America and China account for 25% of total consumption each, and Japan accounts for 1213%. The demand for tungsten in the CIS countries is estimated at 3,000 tons of metal per year.
More than half (58%) of all metal consumed is used in the production of tungsten carbide, almost a quarter (23%) in the form of various alloys and steels. The production of tungsten “roll” (filaments for incandescent lamps, electrical contacts, etc.) accounts for 8% of tungsten produced, and the remaining 9% is used in the production of pigments and catalysts.
Processing of tungsten raw materials.
The primary ore contains about 0.5% tungsten oxide. After flotation and separation of non-magnetic components, a rock containing about 70% WO 3 remains. The enriched ore (and oxidized tungsten scrap) is then leached with sodium carbonate or hydroxide:
4FeWO 4 + O 2 + 4Na 2 CO 3 = 4NaWO 4 + 2Fe 2 O 3 + 4CO 2
6MnWO 4 + O 2 + 6Na 2 CO 3 = 6Na 2 WO 4 + 2Mn 3 O 4 + 6CO 2
WO 3 + Na 2 CO 3 = Na 2 WO 4 + CO 2
WO 3 + 2NaOH = Na 2 WO 4 + H 2 O
Na 2 WO 4 + CaCl 2 = 2NaCl + CaWO 4 Ї.
The resulting solution is freed from mechanical impurities and then processed. Initially, calcium tungstate is precipitated, followed by its decomposition with hydrochloric acid and dissolution of the resulting WO 3 in aqueous ammonia. Sometimes purification of primary sodium tungstate is carried out using ion exchange resins. The final product of the process is ammonium paratungstate:
CaWO 4 + 2HCl = H 2 WO 4 Ї + CaCl 2
H 2 WO 4 = WO 3 + H 2 O
WO3 + 2NH3 · H 2 O (conc.) = (NH 4) 2 WO 4 + H 2 O
12(NH 4) 2 WO 4 + 14HCl (highly diluted) = (NH 4) 10 H 2 W 12 O 42 + 14NH 4 Cl + 6H 2 O
Another way to separate tungsten from enriched ore is by treating it with chlorine or hydrogen chloride. This method is based on the relatively low boiling point of tungsten chlorides and oxochlorides (300 ° C). The method is used to obtain especially pure tungsten.
Wolframite concentrate can be fused directly with coal or coke in an electric arc chamber. This produces ferrotungsten, which is used in the manufacture of alloys in the steel industry. Pure scheelite concentrate can also be added to the steel melt.
About 30% of global tungsten consumption is achieved through the processing of secondary raw materials. Contaminated tungsten carbide scrap, shavings, sawdust and tungsten powder residues are oxidized and converted into ammonium paratungstate. Scrap of high-speed steels is utilized in the production of the same steels (up to 60-70% of the total melt). Tungsten scrap from incandescent lamps, electrodes and chemical reagents is practically not recycled.
The main intermediate product in the production of tungsten is ammonium paratungstate (NH 4) 10 W 12 O 41 · 5H 2 O. It is also the main transported tungsten compound. By calcining ammonium paratungstate, tungsten(VI) oxide is obtained, which is then treated with hydrogen at 700–1000 ° C to obtain metal tungsten powder. By sintering it with carbon powder at 900–2200° C (carburization process), tungsten carbide is obtained.
In 2002, the price of ammonium paratungstate, the main commercial tungsten compound, was about $9,000 per ton in terms of metal. Recently, there has been a downward trend in prices for tungsten products due to large supply from China and the countries of the former USSR.
In Russia, tungsten products are produced by: Skopinsky Hydrometallurgical Plant "Metallurg" (Ryazan region, tungsten concentrate and anhydride), Vladikavkaz Plant "Pobedit" (North Ossetia, tungsten powder and ingots), Nalchik Hydrometallurgical Plant (Kabardino-Balkaria, metal tungsten, tungsten carbide ), Kirovgrad Hard Alloy Plant (Sverdlovsk region, tungsten carbide, tungsten powder), Elektrostal (Moscow region, ammonium paratungstate, tungsten carbide), Chelyabinsk Electrometallurgical Plant (ferrotungsten).
Properties of a simple substance.
Tungsten metal has a light gray color. After carbon, it has the highest melting point of all simple substances. Its value is determined within 33873422° C. Tungsten has excellent mechanical properties at high temperatures and the lowest coefficient of expansion among all metals. Boiling point 54005700° C. Tungsten one of the heaviest metals with a density of 19250 kg/m 3. The electrical conductivity of tungsten at 0° C is about 28% of the electrical conductivity of silver, which is the most electrically conductive metal. Pure tungsten is quite easy to process, but it usually contains impurities of carbon and oxygen, which gives the metal its well-known hardness.
Tungsten has a very high tensile and compressive modulus, very high thermal creep resistance, high thermal and electrical conductivity, and a high electron emission coefficient, which can be further improved by alloying tungsten with certain metal oxides.
Tungsten is chemically resistant. Hydrochloric, sulfuric, nitric, hydrofluoric acids, aqua regia, aqueous solution of sodium hydroxide, ammonia (up to 700° C), mercury and mercury vapor, air and oxygen (up to 400° C), water, hydrogen, nitrogen, carbon monoxide (up to 800° C), hydrogen chloride (up to 600° C) have no effect on tungsten. Ammonia mixed with hydrogen peroxide, liquid and boiling sulfur, chlorine (over 250 ° C), hydrogen sulfide at red heat, hot aqua regia, a mixture of hydrofluoric and nitric acids, melts of nitrate, nitrite, potassium chlorate, lead dioxide react with tungsten. , sodium nitrite, hot nitric acid, fluorine, bromine, iodine. Tungsten carbide is formed by the interaction of carbon with tungsten at temperatures above 1400 ° C, oxide by interaction with water vapor and sulfur dioxide (at red heat), carbon dioxide (above 1200 ° C), oxides of aluminum, magnesium and thorium.
Properties of the most important tungsten compounds.
Among the most important compounds of tungsten are its oxide, chloride, carbide and ammonium paratungstate.
Tungsten(VI) oxide WO 3 crystalline substance of light yellow color, when heated it becomes orange, melting point 1473 ° C, boiling point 1800 ° C. The corresponding tungstic acid is unstable, in an aqueous solution a dihydrate precipitates, losing one molecule of water at 70-100 ° C, and the second at 180-350 ° C. When WO 3 reacts with alkalis, tungstates are formed.
Tungstic acid anions tend to form polycompounds. When reacting with concentrated acids, mixed anhydrides are formed:
12WO 3 + H 3 PO 4 (boiling, conc.) = H 3
When tungsten oxide reacts with metallic sodium, non-stoichiometric sodium tungstate is formed, called “tungsten bronze”:
WO 3+ x Na = Na x WO 3
When tungsten oxide is reduced with hydrogen at the moment of separation, hydrated oxides with a mixed oxidation state are formed “tungsten blues” WO 3 n(OH) n , n= 0.50.1.
WO 3 + Zn + HCl ® (“blue”), W 2 O 5 (OH) (brown)
Tungsten(VI) oxide intermediate product in the production of tungsten and its compounds. It is a component of some industrially important hydrogenation catalysts and ceramic pigments.
Higher tungsten chloride WCl 6 is formed by the reaction of tungsten oxide (or tungsten metal) with chlorine (as well as fluorine) or carbon tetrachloride. It differs from other tungsten compounds by its low boiling point (347 ° C). By its chemical nature, chloride is an acid chloride of tungstic acid, therefore, when interacting with water, incomplete acid chlorides are formed, and when interacting with alkalis, salts are formed. As a result of the reduction of tungsten chloride with aluminum in the presence of carbon monoxide, tungsten carbonyl is formed:
WCl 6 + 2Al + 6CO = Ї + 2AlCl 3 (in ether)
Tungsten carbide WC is obtained by reacting powdered tungsten with coal in a reducing atmosphere. Its hardness, comparable to diamond, determines its scope of application.
Ammonium tungstate (NH 4) 2 WO 4 is stable only in ammonia solution. In dilute hydrochloric acid, ammonium paratungstate (NH 4) 10 H 2 W 12 O 42, which is the main tungsten intermediate on the world market, precipitates. Ammonium paratungstate easily decomposes when heated:
(NH 4) 10 H 2 W 12 O 42 = 10NH 3 + 12WO 3 + 6H 2 O (400 500° C)
Application of tungsten.
The use of pure metal and tungsten-containing alloys is based mainly on their refractoriness, hardness and chemical resistance. Pure tungsten is used for the manufacture of filaments of electric incandescent lamps and cathode ray tubes, in the production of crucibles for the evaporation of metals, in the contacts of automobile ignition distributors, in the targets of X-ray tubes; as windings and heating elements of electric furnaces and as a structural material for space and other vehicles operated at high temperatures. High-speed steels (17.5-18.5% tungsten), stellite (cobalt-based with the addition of Cr, W, C), hastalloy (Ni-based stainless steel) and many other alloys contain tungsten. The basis for the production of tool and heat-resistant alloys is ferrotungsten (68-86% W, up to 7% Mo and iron), which is easily obtained by direct reduction of tungsten or scheelite concentrates. “Win” a very hard alloy containing 8087% tungsten, 615% cobalt, 57% carbon, indispensable in metal processing, in the mining and oil industries.
Calcium and magnesium tungstates are widely used in fluorescent devices, and other tungsten salts are used in the chemical and tanning industries. Tungsten disulfide is a dry high-temperature lubricant, stable up to 500° C. Tungsten bronzes and other compounds of the element are used in the manufacture of paints. Many tungsten compounds are excellent catalysts.
For many years after its discovery, tungsten remained a laboratory rarity; only in 1847 did Oxland receive a patent for the production of sodium tungstate, tungstic acid and tungsten from cassiterite (tin stone). The second patent, obtained by Oxland in 1857, described the production of iron-tungsten alloys, which form the basis of modern high-speed steels.
In the middle of the 19th century. The first attempts were made to use tungsten in steel production, but for a long time it was not possible to introduce these developments into industry due to the high price of the metal. The increased demand for alloy and high-strength steels led to the launch of the production of high-speed steels at Bethlehem Steel. Samples of these alloys were first presented in 1900 at the World Exhibition in Paris.
Tungsten filament manufacturing technology and its history.
The production volumes of tungsten wire have a small share among all tungsten applications, but the development of the technology for its production played a key role in the development of powder metallurgy of refractory compounds.
Since 1878, when Swan demonstrated the eight- and sixteen-candle carbon lamps he had invented in Newcastle, a search had been going on for a more suitable material for making incandescent filaments. The first coal lamp had an efficiency of only 1 lumen/watt, which was increased over the next 20 years by modifications in coal processing methods by two and a half times. By 1898, the light output of such bulbs was 3 lumens/watt. In those days, carbon filaments were heated by passing an electric current in an atmosphere of heavy hydrocarbon vapors. During the pyrolysis of the latter, the resulting carbon filled the pores and irregularities of the thread, giving it a bright metallic shine.
At the end of the 19th century. von Welsbach was the first to produce metal filament for incandescent lamps. He made it from osmium (T pl = 2700 ° C). Osmium filaments had an efficiency of 6 lumens/watt, however, osmium is a rare and extremely expensive platinum group element, so it was not widely used in the manufacture of household devices. Tantalum, with a melting point of 2996° C, was widely used in the form of drawn wire from 1903 to 1911 thanks to the work of von Bolton of Siemens and Halske. The efficiency of tantalum lamps was 7 lumens/watt.
Tungsten began to be used in incandescent lamps in 1904 and replaced all other metals in this capacity by 1911. A conventional incandescent lamp with a tungsten filament has a glow of 12 lumens/watt, and lamps operating under high voltage have a luminescence of 22 lumens/watt. Modern tungsten cathode fluorescent lamps have an efficiency of about 50 lumens/watt.
In 1904, Siemens-Halske tried to apply the wire drawing process developed for tantalum to more refractory metals such as tungsten and thorium. The rigidity and lack of malleability of tungsten did not allow the process to proceed smoothly. However, it was later shown in 1913-1914 that molten tungsten could be rolled out and drawn using a partial reduction procedure. An electric arc was passed between a tungsten rod and a partially molten tungsten droplet placed in a graphite crucible coated inside with tungsten powder and located in a hydrogen atmosphere. Thus, small drops of molten tungsten were obtained, about 10 mm in diameter and 20-30 mm in length. Although with difficulty, it was already possible to work with them.
During the same years, Just and Hannaman patented a process for making tungsten filaments. Fine metal powder was mixed with an organic binder, the resulting paste was passed through dies and heated in a special atmosphere to remove the binder, resulting in a thin thread of pure tungsten.
In 1906–1907 the well-known extrusion process was developed and used until the early 1910s. Very finely ground black tungsten powder was mixed with dextrin or starch until a plastic mass was formed. Using hydraulic pressure, this mass was forced through thin diamond sieves. The resulting thread was strong enough to be wound onto spools and dried. Next, the threads were cut into “pins,” which were heated in an inert gas atmosphere to a red-hot temperature to remove residual moisture and light hydrocarbons. Each “pin” was secured in a clamp and heated in a hydrogen atmosphere until it glowed brightly by passing an electric current. This led to the final removal of unwanted impurities. At high temperatures, individual small particles of tungsten fuse and form a homogeneous solid metal filament. These threads are elastic, although fragile.
At the beginning of the 20th century. Yust and Hannaman developed another process that was notable for its originality. A carbon filament with a diameter of 0.02 mm was coated with tungsten by heating in an atmosphere of hydrogen and tungsten hexachloride vapor. The thread coated in this way was heated to a bright glow in hydrogen at reduced pressure. In this case, the tungsten shell and the carbon core were completely fused with each other, forming tungsten carbide. The resulting thread was white and brittle. The filament was then heated in a stream of hydrogen, which reacted with the carbon, leaving a compact filament of pure tungsten. The threads had the same characteristics as those obtained during the extrusion process.
In 1909, the American Coolidge managed to obtain malleable tungsten without the use of fillers, but only with the help of reasonable temperature and mechanical processing. The main problem in producing tungsten wire was the rapid oxidation of tungsten at high temperatures and the presence of a grain structure in the resulting tungsten, which led to its brittleness.
Modern production of tungsten wire is a complex and precise technological process. The starting material is powdered tungsten obtained by reducing ammonium paratungstate.
Tungsten powder used for wire production must be of high purity. Typically, tungsten powders of different origins are mixed to homogenize the quality of the metal. They are mixed in mills and, to avoid oxidation of the metal heated by friction, a stream of nitrogen is passed into the chamber. Then the powder is pressed in steel molds using hydraulic or pneumatic presses (525 kg/mm 2). When contaminated powders are used, the compact becomes brittle and a fully oxidizable organic binder is added to eliminate this effect. At the next stage, preliminary sintering of the bars is carried out. When heating and cooling compacts in a hydrogen flow, their mechanical properties improve. The compacts still remain quite fragile, and their density is 60-70% of the density of tungsten, so the bars are subjected to high-temperature sintering. The rod is clamped between contacts cooled by water, and in an atmosphere of dry hydrogen, a current is passed through it to heat it almost to the melting point. Due to heating, tungsten is sintered and its density increases to 85–95% of the crystalline value, at the same time the grain sizes increase and tungsten crystals grow. This is followed by forging at high (12001500° C) temperatures. In a special apparatus, the rods are passed through a chamber, which is compressed with a hammer. During one pass, the diameter of the rod decreases by 12%. When forged, tungsten crystals elongate, creating a fibrillar structure. After forging, wire drawing follows. The rods are lubricated and passed through diamond or tungsten carbide screens. The degree of drawing depends on the purpose of the resulting products. The diameter of the resulting wire is about 13 microns.
Biological role of tungsten
limited. Its neighbor in the group, molybdenum, is indispensable in enzymes that ensure the fixation of atmospheric nitrogen. Previously, tungsten was used in biochemical studies only as an antagonist of molybdenum, i.e. replacing molybdenum with tungsten in the active site of the enzyme led to its deactivation. On the contrary, enzymes that are deactivated when replacing tungsten with molybdenum are found in thermophilic microorganisms. Among them are formate dehydrogenases, aldehyde ferredoxin oxidoreductases; formaldehyde ferredo-xyn oxidoreductase; acetylene hydratase; carboxylic acid reductase. The structures of some of these enzymes, such as aldehyde ferredoxin oxidoreductase, have now been determined.
Severe consequences of exposure to tungsten and its compounds on humans have not been identified. Long-term exposure to large doses of tungsten dust can cause pneumoconiosis, a disease caused by all heavy powders entering the lungs. The most common symptoms of this syndrome are cough, breathing problems, atopic asthma, changes in the lungs, the manifestation of which decreases after cessation of contact with metal.
Materials on the Internet: http://minerals.usgs.gov/minerals/pubs/commodity/tungsten/
Yuri Krutyakov
Literature:
Colin J. Smithells Tungsten, M., Metallurgizdat, 1958
Agte K., Vacek I. Tungsten and molybdenum, M., Energy, 1964
Figurovsky N.A. The discovery of elements and their origin is named yy. M., Nauka, 1970
Popular library of chemical elements. M., Nauka, 1983
US Geological Survey Minerals Yearbook 2002
Lvov N.P., Nosikov A.N., Antipov A.N. Tungsten enzymes, vol. 6, 7. Biochemistry, 2002
The article covers the process of tungsten production from the stage of ore enrichment to the stage of obtaining blanks in the form of bars and ingots. The characteristic features of each stage are noted.
Particular attention in the article is paid to products (wire, rods, sheets, etc.). The processes for manufacturing certain tungsten products, their characteristic features and areas of application are described.
Chapter 1. Tungsten. Properties and applications of tungsten
Tungsten (denoted W) is a chemical element of group VI of the 6th period of the D.I. table. Mendeleev, has number 74; light gray transition metal. The most refractory metal, has a melting point t pl = 3380 °C. From the point of view of the use of the metal tungsten, its most important properties are density, melting point, electrical resistance, and coefficient of linear expansion.§1. Properties of tungsten
| Property | Meaning |
|---|---|
| Physical properties | |
| Atomic number | 74 |
| Atomic mass, a.m.u. (g/mol) | 183,84 |
| Atomic diameter, nm | 0,274 |
| Density, g/cm 3 | 19,3 |
| Melting point, °C | 3380 |
| Boiling point, °C | 5900 |
| Specific heat capacity, J/(g K) | 0,147 |
| Thermal conductivity, W/(m K) | 129 |
| Electrical resistance, µOhm cm | 5,5 |
| Coefficient of linear thermal expansion, 10 -6 m/mK | 4,32 |
| Mechanical properties | |
| Young's modulus, GPa | 415,0 |
| Shear modulus, GPa | 151,0 |
| Poisson's ratio | 0,29 |
| Tensile strength σ B, MPa | 800-1100 |
| Relative elongation δ, % | 0 |
The metal has a very high boiling point (5900 °C) and a very low evaporation rate even at a temperature of 2000 °C. The electrical conductivity of tungsten is almost three times lower than the electrical conductivity of copper. Properties that limit the scope of tungsten application include high density, high tendency to brittleness at low temperatures, and low oxidation resistance at low temperatures.
Tungsten is similar in appearance to steel. Used to create alloys with high strength. Tungsten can be processed (forging, rolling and drawing) only when heated. The heating temperature depends on the type of processing. For example, forging rods is carried out by heating the workpiece to 1450-1500 °C.
§2. Tungsten grades
| Tungsten grade | Brand characteristics | Purpose of introducing the additive |
|---|---|---|
| HF | Tungsten pure (without additives) | - |
| VA | Tungsten with silicon-alkali and aluminum additives | Increasing the temperature of primary recrystallization, strength after annealing, dimensional stability at high temperatures |
| VM | Tungsten with silicon-alkali and thorium additives | Increasing the recrystallization temperature and increasing the strength of tungsten at high temperatures |
| VT | Tungsten with thorium oxide additive | |
| IN AND | Tungsten with yttrium oxide additive | Increasing the emissive properties of tungsten |
| VL | Tungsten with lanthanum oxide additive | Increasing the emissive properties of tungsten |
| VR | Tungsten-rhenium alloy | An increase in the ductility of tungsten after high-temperature treatment, an increase in the temperature of primary recrystallization, strength at high temperatures, electrical resistivity, and e.m.f. |
| VRN | Tungsten without additives, in which a high content of impurities is allowed | - |
| MV | Molybdenum and tungsten alloys | Increasing the strength of molybdenum while maintaining ductility after annealing |
§3. Applications of tungsten
Tungsten is widely used due to its unique properties. In industry, tungsten is used as a pure metal and in a number of alloys.Main areas of application of tungsten
1. Special steels
Tungsten is used as one of the main components or alloying element in the production of high-speed steels (contain 9-24% tungsten W), as well as tool steels (0.8-1.2% tungsten W - tungsten tool steels; 2-2.7 % tungsten W - chrome-tungsten tool steels (also contain chromium Cr and silicon Si); 2-9% tungsten W - chrome-tungsten tool steels (also contain chrome Cr); 0.5-1.6% tungsten W - chrome-tungsten manganese tool steels (also contain chromium Cr and manganese Mn). Drills, cutters, punches, dies, etc. are made from the listed steels. Examples of high-speed steels include R6M5, R6M5K5, R6M5F3. The letter “P” means that the steel is high-speed, the letters “M” and “K” - that the steel is alloyed with molybdenum and cobalt, respectively. Tungsten is also part of magnetic steels, which are divided into tungsten and tungsten-cobalt.
2. Hard alloys based on tungsten carbide
Tungsten carbide (WC, W 2 C) - a compound of tungsten with carbon (see). It has high hardness, wear resistance and refractoriness. On its basis, the most productive tool hard alloys have been created, which contain 85-95% WC and 5-14% Co. Working parts of cutting and drilling tools are made from hard alloys.
3. Heat-resistant and wear-resistant alloys
These alloys take advantage of the refractoriness of tungsten. Alloys of tungsten with cobalt and chromium - stellites (3-5% W, 25-35% Cr, 45-65% Co) have become widespread. They are usually applied using surfacing to the surfaces of heavily worn machine parts.
4. Contact alloys and “heavy alloys”
These alloys include tungsten-copper and tungsten-silver alloys. These are quite effective contact materials for the manufacture of working parts of switches, switches, electrodes for spot welding, etc.
5. Electrovacuum and electric lighting equipment
Tungsten in the form of wire, strip and various forged parts is used in the production of electric lamps, radio electronics and x-ray technology. Tungsten is the best material for filaments and filaments. Tungsten wire and rods serve as electric heaters for high-temperature furnaces (up to ~3000 °C). Tungsten heaters operate in an atmosphere of hydrogen, inert gas or vacuum.
6. Welding electrodes
A very important application of tungsten is welding. Electrodes for arc welding are made from tungsten (see). Tungsten electrodes are non-consumable.
Chapter 2. Tungsten production
§1. The process of obtaining the refractory metal tungsten
Tungsten is usually classified as a broad group of rare metals. In addition to this metal, this group includes molybdenum, rubidium and others. Rare metals are characterized by relatively small scales of production and consumption, as well as low abundance in the earth's crust. No rare metal is obtained by direct reduction from raw materials. First, the raw materials are processed into chemical compounds. In addition, all rare metal ores undergo additional enrichment before processing.In the process of obtaining a rare metal, three main stages can be distinguished:
- Decomposition of ore material is the separation of the extracted metal from the bulk of the processed raw material and its concentration in a solution or sediment.
- Obtaining pure chemical compounds - isolating and purifying a chemical compound.
- Isolation of metal from the resulting compound is the production of pure rare metals.
- Tungsten ore beneficiation. It is produced using gravity, flotation, magnetic or electrostatic separation. As a result of enrichment, a tungsten concentrate is obtained containing 55 - 65% tungsten anhydride (trioxide) WO 3. The content of impurities in tungsten concentrates is controlled - phosphorus, sulfur, arsenic, tin, copper, antimony and bismuth.
- Preparation of tungsten trioxide (anhydride) WO 3, which serves as the feedstock for the production of metal tungsten or its carbide. To do this, it is necessary to perform a number of actions, such as decomposition of concentrates, leaching of the alloy or sinter, obtaining technical tungstic acid, etc. The result should be a product containing 99.90 - 99.95% WO 3.
- Preparation of tungsten powder. Pure metal in powder form can be obtained from tungsten anhydride WO 3 . To do this, a process of anhydride reduction with hydrogen or carbon is carried out. Carbon reduction is used less frequently, since in this process WO 3 is saturated with carbides, which makes the metal more brittle and impairs machinability. When obtaining tungsten powder, special methods are used to control its chemical composition, grain size and shape, and granulometric composition. For example, a rapid increase in temperature and a low rate of hydrogen supply contribute to an increase in the size of powder particles.
- Production of compact tungsten. Compact tungsten, usually in the form of bars or ingots, is a blank for the production of semi-finished products such as wire, rod, strip, and so on.
§2. Production of compact tungsten
There are two ways to produce compact tungsten. The first is to use powder metallurgy methods. The second is by melting in electric arc furnaces with a consumable electrode.Powder metallurgy methods
This method of producing malleable tungsten is the most common, as it allows for a more even distribution of additives that give tungsten special properties (heat resistance, emissive properties, etc.).
The process of producing compact tungsten using this method consists of several stages:
- pressing bars from metal powder;
- low-temperature (preliminary) sintering of workpieces;
- sintering (welding) of workpieces;
- processing of workpieces in order to obtain semi-finished products - tungsten wire, tape, tungsten rods; Usually the workpieces are processed by pressure (forging) or subjected to mechanical cutting (for example, grinding, polishing).
Using the described powder metallurgy method, tungsten rods with a square cross-section from 8x8 to 40x40 mm and a length of 280-650 mm are obtained. At room temperature they have good strength, but are very brittle. It is worth noting that strength and fragility (the opposite property - plasticity) belong to different groups of properties. Strength is a mechanical property of a material, plasticity is a technological property. Ductility determines the suitability of a material for forging. If a material is difficult to forge, then it is brittle. To improve ductility, tungsten rods are forged in a heated state.
However, the method described above cannot produce large-sized workpieces of large mass, which is a significant limitation. To obtain large-sized workpieces, the mass of which reaches several hundred kilograms, hydrostatic pressing is used. This method makes it possible to produce blanks of cylindrical and rectangular cross-sections, pipes and other products of complex shape. At the same time, they have a uniform density and do not contain cracks or other defects.
Fuse
Melting is used to produce compact tungsten in the form of large-sized billets (from 200 to 3000 kg), intended for rolling, pipe drawing, and production of casting products. Melting is carried out in electric arc furnaces with a consumable electrode and/or electron beam melting.
In arc melting, packages of sintered rods or sintered billets of hydrostatic pressing serve as electrodes. Melting is carried out in a vacuum or rarefied atmosphere of hydrogen. The result is tungsten ingots. Tungsten ingots have a coarse-crystalline structure and increased fragility, which is caused by a high content of impurities.
To reduce the impurity content, tungsten is initially melted in an electron beam furnace. But after this type of smelting, tungsten also has a coarse-crystalline structure. Therefore, in order to reduce the grain size, the resulting ingots are melted in an electric arc furnace, adding small amounts of zirconium or niobium carbides, as well as alloying elements to impart special properties.
To produce fine-grained tungsten ingots, as well as to manufacture parts by casting, arc skull melting is used with metal casting into a mold.
Chapter 3. Tungsten products. Rods, wire, strips, powder
§1. Tungsten rods
ProductionTungsten rods are one of the most common types of products made from the refractory metal tungsten. The starting material for the production of rods is rod.
To obtain tungsten rods, the rod is forged on a rotary forging machine. Forging is carried out in a heated state, since tungsten is very brittle at room temperature. Several stages of forging can be distinguished. At each subsequent stage, rods of smaller diameter are obtained than at the previous one.
During the first forging, you can obtain tungsten rods with a diameter of up to 7 mm (provided that the rod has a side length of 10-15 cm). Forging is carried out at a workpiece temperature of 1450-1500 °C. Molybdenum is usually used as the heater material. After the second forging, rods with a diameter of up to 4.5 mm are obtained. It is produced at a temperature of 1300-1250 °C. With further forging, tungsten rods with a diameter of up to 2.75 mm are obtained. It is worth noting that tungsten rods of the VT, VL and VI brands are produced at a higher temperature than rods of the VA and VC brands.
If tungsten ingots, which are obtained by melting, are used as the initial workpiece, then hot forging is not carried out. This is due to the fact that these ingots have a coarse, coarse-crystalline structure, and their hot forging can lead to cracking and destruction.
In this case, tungsten ingots are subjected to double hot pressing (the degree of deformation is about 90%). The first pressing is carried out at a temperature of 1800-1900 °C, the second - 1350-1500 °C. The blanks are then hot forged to produce tungsten rods.
Application
Tungsten rods are widely used in various industries. One of the most common applications is non-consumable welding electrodes. Tungsten rods of brands VT, VI, VL are suitable for such purposes. Also, tungsten rods of the VA, VR, MV brands are used as heaters. Tungsten heaters operate in furnaces up to 3000 °C in an atmosphere of hydrogen, inert gas or vacuum. Tungsten rods can serve as cathodes for radio tubes, electronic and gas-discharge devices.
§2. Tungsten electrodes
Arc weldingWelding electrodes are one of the most important components required for welding. They are most widely used in arc welding. It belongs to the thermal class of welding, in which melting is carried out due to thermal energy. Arc welding (manual, semi-automatic and automatic) is the most common welding process. Thermal energy is created by a voltaic arc that burns between the electrode and the product (part, workpiece). An arc is a powerful, stable electrical discharge in an ionized atmosphere of gases and metal vapors. The electrode applies electrical current to the welding site to create an arc.
Welding electrodes
A welding electrode is a wire rod with a coating applied to it (or without coating). There is a large variety of electrodes for welding. They differ in chemical composition, length, diameter, a certain type of electrodes is suitable for welding certain metals and alloys, etc. etc. The division of welding electrodes into consumable and non-consumable is one of the most important types of their classification.
Consumable welding electrodes are melted during the welding process; their metal, together with the molten metal of the part being welded, is used to replenish the weld pool. Such electrodes are made of steel and copper.
Non-consumable electrodes do not melt during welding. This type includes carbon and tungsten electrodes. When welding using non-consumable tungsten electrodes, it is necessary to supply a filler material (usually a welding wire or rod), which melts and, together with the molten material of the part being welded, forms a weld pool.
Also, welding electrodes can be coated or uncoated. Coverage is important. Its components can ensure the production of weld metal of the specified composition and properties, stable arc burning, and protection of the molten metal from exposure to air. Accordingly, the components of the coating can be alloying, stabilizing, gas-forming, slag-forming, deoxidizing, and the coating itself can be acidic, rutile, basic or cellulose.
Tungsten Welding Electrodes
As noted earlier, tungsten electrodes are non-consumable and are used together with filler wire during welding. These electrodes are mainly used for welding non-ferrous metals and their alloys (tungsten electrode with zirconium additive), high-alloy steels (tungsten electrode with thorium EVT additive), and the tungsten electrode is well suited for obtaining a weld of increased strength, and the parts being welded can be of different chemical composition.
Welding using tungsten electrodes in an argon environment is quite common. This environment has a positive effect on the welding process and the quality of the weld. Tungsten electrodes can be made from pure tungsten or contain various additives that improve the quality of the welding process and weld. A feature of non-consumable welding electrodes made of pure tungsten (for example, an EHF tungsten electrode) is that the arc ignitability is not very good.
Ignition of the arc takes place in three stages:
- short circuit of the electrode to the workpiece;
- removal of the electrode to a small distance;
- occurrence of a stable arc discharge.
Argon arc welding (Arc welding with a non-consumable tungsten electrode in an argon environment) This type of welding has proven itself in welding non-ferrous metals such as molybdenum, titanium, nickel, as well as high-alloy steels. This is a type of arc welding where the source of high temperature required to create a weld pool is an electric current. In this type of argon arc welding, the main elements are a tungsten electrode and the inert gas argon. During welding, argon is supplied to the tungsten electrode and protects it, the arc zone and the weld pool from the atmospheric gas mixture (nitrogen, hydrogen, carbon dioxide). This protection greatly improves the quality characteristics of the weld and also protects tungsten welding electrodes from rapid combustion in air. Argon gas can be used when welding a large number of metals and alloys, since it is inert.
Standards for Tungsten Electrodes
In Russia, non-consumable tungsten electrodes are produced in accordance with the requirements of standards and technical specifications. Among them: GOST 23949-80“Tungsten welding electrodes are non-consumable. Technical conditions”; TU 48-19-27-88“Lanthanum tungsten in the form of rods. Technical conditions”; TU 48-19-221-83“Rods made of itrated tungsten grade SVI-1. Technical conditions”; TU 48-19-527-83“Tungsten welding electrodes, non-consumable EVCh and EVL-2. Technical conditions".
§3. Tungsten wire
ProductionTungsten wire is one of the most common types of products made from this refractory metal. The starting material for its manufacture is forged tungsten rods with a diameter of 2.75 mm.
Wire drawing is carried out at a temperature of 1000 °C at the beginning of the process and 400-600 °C at the end. In this case, not only the wire, but also the die is heated. Heating is carried out by a gas burner flame or an electric heater.
Drawing of wire with a diameter of up to 1.26 mm is carried out on a straight chain drawing mill, within a diameter of 1.25-0.5 mm - on a block mill with a coil diameter of ~1000 mm, with a diameter of 0.5-0.25 - on single drawing machines .
As a result of forging and drawing, the structure of the workpiece turns into a fibrous one, which consists of crystal fragments elongated along the processing axis. This structure leads to a sharp increase in the strength of tungsten wire.
After drawing, the tungsten wire is coated with graphite lubricant. The surface of the wire must be cleaned. Cleaning is carried out using annealing, chemical or electrolytic etching, and electrolytic polishing. Polishing can increase the mechanical strength of tungsten wire by 20-25%.
Application
Tungsten wire is used for the manufacture of resistance elements in heating furnaces operating in an atmosphere of hydrogen, neutral gas or vacuum at temperatures up to 3000 °C. Tungsten wire is also used for the production of thermocouples. For this purpose, tungsten-rhenium alloy with 5% rhenium and tungsten-rhenium alloy with 20% rhenium are used ( VR 5/20).
IN GOST 18903-73“The wire is tungsten. Assortment” indicates the areas of application of wire grades VA, VM, VRN, VT-7, VT-10, VT-15. Tungsten wire VA, depending on the group, surface and metal condition, diameter, is used for the manufacture of spirals of incandescent lamps and other light sources, spiral cathodes and heaters of electronic devices, springs of semiconductor devices, loop heaters, non-spiral cathodes, grids, springs of electronic devices. VRN brand wire is used to produce bushings, traverses and other parts of devices that do not require the use of tungsten with special additives.
§4. Tungsten powder
Pure tungsten powder serves as the raw material for the production of compact tungsten (see). Tungsten carbide WC, which is also a powder in appearance, is used for the manufacture of hard alloys.Depending on the purpose, tungsten powders are distinguished by the average particle size, the set of grains and other parameters.
The main impurity in tungsten powders is oxygen (0.05 - 0.3%). Metal impurities are contained in tungsten powders in very small quantities. Often, additives from other metals are added to tungsten powders, which improve certain properties of the final product. Aluminum, thorium, lanthanum and others are often used as additives.
Tungsten powder VA, which is used for the manufacture of wire, contains evenly distributed silicon-alkali and aluminum additives (0.32% K 2 O; 0.45% SiO 2; 0.03% Al 2 O 3), powder made of refractory metal tungsten grade VT - thorium oxide additive (0.7 - 5%), VL - lanthanum oxide additive (~1% La 2 O 3), VI - yttrium oxide additive (~3% Y 2 O 3), VM - silica-alkali and thorium additives ( 0.32% K 2 O; 0.45% SiO 2; 0.25% ThO 2).
§5. Tungsten strips (sheets, tapes, foil, plates)
ProductionAs a rule, flat rolled products from tungsten - sheets, strips, plates, foil - are produced using two operations - flat forging and rolling. Tungsten rods of various sizes are used as a workpiece.
First, the tungsten bars are flat forged using a pneumatic hammer. Forging is carried out at a temperature of 1500-1700 °C, which decreases to 1200-1300 °C as deformation occurs. The forging operation continues until a forging is obtained with a thickness of 8-10 mm (with a cross-section of the bar 25x25 mm) or 4-5 mm (with a cross-section of the bar 12x12 mm).
The resulting forgings are then rolled in rolling mills. At the beginning of the rolling process, the workpieces are heated to 1300-1400 °C, then the temperature is lowered to 1000-1200 °C. Hot rolling produces tungsten sheets, strips and plates up to 0.6 mm thick. To obtain sheets, strips and plates of smaller sizes, cold rolling is carried out. To obtain thin sheets of tungsten up to 0.125 mm thick and strips (foil) 0.02-0.03 mm thick, rolling in packages is used. The stack consists of several tungsten strips of equal thickness and thicker molybdenum plates that lie on top of the tungsten strips. Molybdenum plates are more ductile and deform faster than tungsten plates. As a result, during rolling they become thinner than tungsten strips. After one or more transitions, the molybdenum plates have to be replaced with new ones so that the thickness of the package remains approximately constant. It is worth noting that the purpose of this process is to produce exactly thin tungsten tape (foil). Molybdenum plates here are a consumable material that is necessary for rolling in packages.
Tungsten ingots, which are obtained by smelting (see). The ingots are pre-pressed. From ingots with a diameter of 70-80 mm, rectangular blanks with a thickness of 20-25 mm and a width of 50-60 mm are obtained by pressing. Then the blanks are deformed on two-roll presses.
Tungsten sheets V-MP
V-MP tungsten sheets are widely used in industry. They are made from tungsten powder of grades PV1 and PV2, containing 99.98% W. V-MP sheets and plates must have a thickness of 0.5-45 mm, cut edges. The sheets can be machined according to customer requirements. GOST 23922-79“V-MP tungsten sheets. Technical conditions".
Application
Due to their high heat resistance, tungsten sheets, like other products made from this refractory metal, are used in conditions of extremely high temperatures. Various equipment for high-temperature furnaces is made from tungsten sheets - heat shields, stands and other fastening elements. Sputtered tungsten targets, which are made in the form of wafers, are used for thin barrier films in the metallization of semiconductor components of integrated circuits. In nuclear power, tungsten sheets are used as shields to attenuate the flow of radioactive radiation.
§6. Tungsten-rhenium alloys
Tungsten-rhenium alloys and products made from these alloys should be included in a separate paragraph. Alloys of the VR5 and VR20 grades will be considered in more detail here.Alloys of these two metals are heat-resistant. Alloying tungsten with other metals lowers its melting point. But when alloying with a refractory metal, the melting point of the alloy does not decrease so significantly. Tungsten (W) and rhenium (Re) are refractory metals.
When rhenium is used as an additive, a “rhenium effect” is observed. 5% rhenium increases the heat resistance and ductility of tungsten. At 20-30% rhenium content, an optimal combination of strength and ductility with high manufacturability is observed. Also, the advantages of tungsten-rhenium alloys include a low evaporation rate at operating temperatures and high electrical resistance.
Tungsten-rhenium alloys, like compact tungsten, are produced by powder metallurgy and smelting.
An interesting area of application for these alloys is temperature measurement. Tungsten-rhenium wire VR5 (5% Re, the rest is W) and BP20 (20% Re, the rest is W) are used for the manufacture of high-temperature thermocouples.
The main advantage of such thermocouples is the range of measured temperatures. Because the alloys VR 5/20 are heat-resistant, then using thermocouples made from appropriate wire, temperatures above 2000 °C can be measured. However, thermocouples of this type must be in an inert environment.
Most often, tungsten-rhenium thermoelectrode wire VR5, VR20 Ø 0.2 is used for the manufacture of thermocouples; 0.35; 0.5 mm.
§7. Tungsten carbides
Very important from a practical point of view are compounds of tungsten with carbon - tungsten carbides. Tungsten forms two carbides - W 2 C and WC. These carbides differ in solubility in carbides of other refractory metals and chemical behavior in various acids. Tungsten carbides, like carbides of other refractory metals, have metallic conductivity and a positive electrical resistivity coefficient. The refractoriness and high hardness of carbides are due to strong interatomic bonds in their crystals. Moreover, the high hardness of WC carbide is maintained at elevated temperatures.The most common method for producing tungsten carbides WC and W 2 C is calcination of a mixture of powdered tungsten with soot in the temperature range of 1000-1500 °C.
Tungsten carbides WC and W 2 C are used mainly for the manufacture of hard alloys.
Hard alloys
There are 2 groups of tungsten carbide-based hard alloys:
- cast carbide (often called cast tungsten carbides);
- sintered hard alloys.
Sintered carbide combine tungsten monocarbide WC and a cementing binder metal, which is usually cobalt, less often nickel. Such alloys can only be produced by powder metallurgy. Tungsten carbide powder and cobalt or nickel powder are mixed, pressed into products of the required shape, and then sintered at temperatures close to the melting point of the cementing metal. In addition to high hardness and wear resistance, these alloys have good strength. Sintered carbide alloys are the most productive modern tool materials for metal cutting. They are also used for the manufacture of dies, dies, and drilling tools. Among the hard alloys for the production of which tungsten carbide is used, it is worth highlighting the alloys of the VK group - tungsten-cobalt hard alloys. Widespread in industry VK8 alloys and VK6. They are used to make cutters, drills, milling cutters, as well as other cutting and drilling tools.
Conclusion
This article discusses various aspects related to the refractory metal TUNGSTEN - properties, applications, production, products.As described in the article, the process of obtaining this metal consists of many stages and is quite labor-intensive. The authors tried to highlight the most significant stages of tungsten production and draw attention to important features.
A review of the properties and applications of tungsten shows that it is a very important material, which in some industries is simply impossible to do without. It has unique properties that in some situations cannot be obtained by using other materials.
A review of industrial tungsten products - wire, rods, sheets, powder - allows you to better understand their features, important properties and specific applications.
Chemistry
Element No. 74 tungsten is usually classified as a rare metal: its content in the earth’s crust is estimated at 0.0055%; it is not found in seawater and could not be detected in the solar spectrum. However, in terms of popularity it can compete with many not at all rare metals, and its minerals were known long before the discovery of the element itself. So, back in the 17th century. in many European countries they knew “tungsten” and “tungsten” - this was the name then for the most common tungsten minerals - wolframite and scheelite. A elementary tungsten was discovered in the last quarter of the 18th century.
Tungsten Ore
Very soon this metal gained practical importance - as an alloying additive. And after the 1900 World Exhibition in Paris, at which samples of high-speed tungsten steel were demonstrated, element No. 74 began to be used by metallurgists in all more or less industrialized countries. The main feature of tungsten as an alloying additive is that it gives steel red resistance - it allows it to maintain hardness and strength at high temperatures. Moreover, when cooled in air (after exposure at temperatures close to red heat), most steels lose their hardness. But tungsten ones do not.
The tool, made of tungsten steel, withstands the enormous speeds of the most intense metalworking processes. The cutting speed of such a tool is measured in tens of meters per second.
Modern high-speed steels contain up to 18% tungsten (or tungsten with molybdenum), 2-7% chromium and a small amount of cobalt. They retain hardness at 700-800° C, while ordinary steel begins to soften when heated to just 200° C. “Stellites” - alloys - have even greater hardness
tungsten and with chromium and cobalt (without iron) and especially tungsten carbides - its compounds with carbon. The “visible” alloy (tungsten carbide, 5-15% cobalt and a small admixture of titanium carbide) is 1.3 times harder than ordinary tungsten steel and retains hardness up to 1000-1100 ° C. Cutters from this alloy can be cut in a minute up to 1500-2000 m of iron filings. They can quickly and accurately process “capricious” materials: bronze and porcelain, glass and ebonite; At the same time, the tool itself wears out very little.
At the beginning of the 20th century. tungsten filament began to be used in light bulbs: it allows the heat to be raised to 2200 ° C and has a high luminous efficiency. And in this capacity, tungsten is absolutely indispensable to this day. Obviously, this is why the electric light bulb is called a “tungsten eye” in one popular song.
Tungsten minerals and ores
Tungsten occurs in nature mainly in the form of oxidized complex compounds formed by tungsten trioxide WO 3 and oxides of iron and manganese or calcium, and sometimes lead, copper, thorium and rare earth elements. The most common mineral, wolframite, is a solid solution of tungstates (tungstic acid salts) of iron and manganese (mFeW0 4 *nMnW0 4). This solution is heavy and hard crystals of brown or black color, depending on which compound predominates in their composition. If there is more pobnerite (manganese compound), the crystals are black, but if iron-containing ferberite predominates, they are brown. Wolframite is paramagnetic and conducts electricity well.
Of other tungsten minerals, scheelite, calcium tungstate CaW04, is of industrial importance. It forms shiny, glass-like crystals that are light yellow, sometimes almost white. Scheelite is non-magnetic, but it has another characteristic feature - the ability to luminesce. When illuminated with ultraviolet rays, it fluoresces bright blue in the dark. The admixture of molybdenum changes the color of the glow of scheelite: it becomes pale blue, and sometimes even cream. This property of scheelite, used in geological exploration, serves as a search feature to detect mineral deposits.
Deposits of tungsten ores are theologically related to the areas of granite distribution. The largest foreign deposits of wolframite and scheelite are located in China, Burma, the USA, Bolivia and Portugal. Our country also has significant reserves of tungsten minerals, their main deposits are located in the Urals, the Caucasus and Transbaikalia.
Large crystals of wolframite or scheelite are very rare. Typically, tungsten minerals are only disseminated into ancient granite rocks - the average tungsten concentration ends up being 1-2% at best. Therefore, it is very difficult to extract tungsten from ores.
How is tungsten obtained?
The first stage is ore enrichment, separating valuable components from the main mass - waste rock. Enrichment methods are common for heavy ores and metals: grinding and flotation with subsequent operations - magnetic separation (for tungsten ores) and oxidative roasting.
The resulting concentrate is most often sintered with an excess of soda to convert tungsten into a soluble compound - sodium tungstate. Another method of obtaining this substance is leaching; tungsten is extracted with a soda solution under pressure and at elevated temperatures (the process takes place in an autoclave), followed by neutralization and precipitation in the form of artificial scheelite, i.e. calcium tungstate. The desire to obtain tungstate is explained by the fact that it is relatively simple to produce, in just two stages:
CaW0 4 → H 2 W0 4 or (NH 4) 2 W0 4 → WO 3, tungsten oxide purified from most of the impurities can be isolated.
There is another way to obtain tungsten oxide - through chlorides. Tungsten concentrate is treated with chlorine gas at elevated temperatures. The resulting tungsten chlorides are quite easily separated from the chlorides of other metals by sublimation, using the temperature difference at which these substances transform into a vapor state. The resulting tungsten chlorides can be converted into oxide, or they can be processed directly into elemental metal.
Converting oxides or chlorides into metal is the next stage in tungsten production. The best reducing agent for tungsten oxide is hydrogen. Reduction with hydrogen produces the purest tungsten metal. The reduction process takes place in tube furnaces, heated in such a way that as it moves through the tube, the “boat” of W0 3 passes through several temperature zones. A stream of dry hydrogen comes towards it. Recovery occurs in both “cold” (450-600° C) and “hot” (750-1100° C) zones; in “cold” ones - to the lower oxide W0 2, then to the elemental metal. Depending on the temperature and duration of the reaction in the “hot” zone, the purity and grain size of the powdered tungsten released on the walls of the “boat” change.
Reduction can occur not only under the influence of hydrogen. In practice, coal is often used. The use of a solid reducing agent somewhat simplifies production, but in this case a higher temperature is required - up to 1300-1400 ° C. In addition, coal and the impurities it always contains react with tungsten, forming carbides and other compounds. This leads to metal contamination. Meanwhile, electrical engineering needs very pure tungsten. Just 0.1% iron makes tungsten brittle and unsuitable for making the finest wire.
The production of tungsten from chlorides is based on the process of pyrolysis. Tungsten forms several compounds with chlorine. With the help of excess chlorine, all of them can be converted into higher chloride - WCl 6, which decomposes into tungsten and chlorine at 1600 ° C. In the presence of hydrogen, this process occurs already at 1000 ° C.
This is how metal tungsten is obtained, but not compact, but in the form of a powder, which is then pressed in a stream of hydrogen at high temperature. At the first stage of pressing (when heated to 1100-1300° C), a porous, brittle ingot is formed. Pressing continues at an even higher temperature, almost reaching the melting point of tungsten at the end. Under these conditions, the metal gradually becomes solid, acquires a fibrous structure, and with it ductility and malleability.
Main properties
Tungsten differs from all other metals in its special heaviness, hardness and refractoriness. The expression “heavy as lead” has long been known. It would be more correct to say: “Heavy as tungsten.” The density of tungsten is almost twice that of lead, more precisely - 1.7 times. At the same time, its atomic mass is slightly lower: 184 versus 207.
In terms of refractoriness and hardness, tungsten and its alloys occupy the highest places among metals. Technically pure tungsten melts at 3410° C, but boils only at 6690° C. This is the temperature on the surface of the Sun!
And the “king of refractoriness” looks rather ordinary. The color of tungsten largely depends on the production method. Fused tungsten is a shiny gray metal that most closely resembles platinum. Tungsten powder is gray, dark gray and even black (the finer the grain, the darker).
Chemical activity
Natural tungsten consists of five stable isotopes with mass numbers from 180 to 186. In addition, in nuclear reactors, as a result of various nuclear reactions, another 8 radioactive isotopes of tungsten are formed with mass numbers from 176 to 188; all of them are relatively short-lived: their half-lives range from several hours to several months.
The seventy-four electrons of the tungsten atom are arranged around the nucleus in such a way that six of them are in outer orbits and can be separated relatively easily. Therefore, the maximum valence of tungsten is six. However, the structure of these outer orbits is special - they consist of two “tiers”: four electrons belong to the penultimate level -d, which is thus less than half filled. (The number of electrons in a filled d level is known to be ten.) These four electrons (obviously unpaired) can easily form a chemical bond. As for the two “outermost” electrons, it is quite easy to tear them off.
It is the structural features of the electron shell that explain the high chemical activity of tungsten. In compounds it is not only hexavalent, but also penta-, tetra-, tri-, bi- and zero-valent. (Only monovalent tungsten compounds are unknown).
The activity of tungsten is manifested in the fact that it reacts with the overwhelming majority of elements, forming many simple and complex compounds. Even in alloys, tungsten is often chemically bonded. And it interacts with oxygen and other oxidizing agents more easily than most heavy metals.
The reaction of tungsten with oxygen occurs when heated, especially easily in the presence of water vapor. If tungsten is heated in air, then at 400-500 ° C a stable lower oxide W0 2 is formed on the metal surface; the entire surface is covered with a brown film. At a higher temperature, the blue intermediate oxide W 4 O 11 is first obtained, and then lemon-yellow tungsten trioxide W0 3, which sublimes at 923 ° C.
Dry fluorine combines with finely ground tungsten even with slight heating. This produces hexafluoride WF6 - a substance that melts at 2.5 ° C and boils at 19.5 ° C. A similar compound - WCl 6 - is obtained by reaction with chlorine, but only at 600 ° C. WCl crystals are blue-steel in color 6 melt at 275° C and boil at 347° C. With bromine and iodine, tungsten forms unstable compounds: penta- and dibromide, tetra- and diiodine.
At high temperatures, tungsten combines with sulfur, selenium and tellurium, with nitrogen and boron, with carbon and silicon. Some of these compounds are distinguished by great hardness and other remarkable properties.
Carbonyl W(CO) 6 is very interesting. Here, tungsten is combined with carbon monoxide and therefore has zero valence. Tungsten carbonyl is unstable; it is obtained under special conditions. At 0°C it is released from the corresponding solution in the form of colorless crystals, at 50°C it sublimes, and at 100°C it completely decomposes. But it is this connection that makes it possible to obtain thin and dense coatings from pure tungsten.
Not only tungsten itself, but also many of its compounds are very active. In particular, tungsten oxide WO 3 is capable of polymerization. As a result, so-called isopolycompounds and heteropolycompounds are formed: the molecules of the latter can contain more than 50 atoms.
Alloys
Tungsten forms alloys with almost all metals, but obtaining them is not so easy. The fact is that generally accepted fusion methods are, as a rule, inapplicable in this case. At the melting point of tungsten, most other metals have already turned into gases or highly volatile liquids. Therefore, alloys containing tungsten are usually produced by powder metallurgy methods.
To avoid oxidation, all operations are carried out in a vacuum or in an argon atmosphere. It's done like this. First, the mixture of metal powders is pressed, then sintered and subjected to arc melting in electric furnaces. Sometimes one tungsten powder is pressed and sintered, and the porous workpiece obtained in this way is impregnated with a liquid melt of another metal: so-called pseudo-alloys are obtained. This method is used when it is necessary to obtain an alloy of tungsten with copper and silver.
With chromium and molybdenum, niobium and tantalum, tungsten produces conventional (homogeneous) alloys in any ratio. Even small additions of tungsten increase the hardness of these metals and their resistance to oxidation.
Alloys with iron, nickel and cobalt are more complex. Here, depending on the ratio of the components, either solid solutions or intermetallic compounds (chemical compounds of metals) are formed, and in the presence of carbon (which is always present in steel), mixed tungsten and iron carbides are formed, giving the metal even greater hardness.
Very complex compounds are formed by alloying tungsten with aluminum, beryllium and titanium: in them there are from 2 to 12 atoms of light metal per one atom of tungsten. These alloys are characterized by heat resistance and resistance to oxidation at high temperatures.
In practice, tungsten alloys are most often used not with one particular metal, but with several. These are, in particular, acid-resistant alloys of tungsten with chromium and cobalt or nickel (amala); They are used to make surgical instruments. The best grades of magnetic steel contain tungsten, iron and cobalt. And in special heat-resistant alloys, in addition to tungsten, there are chromium, nickel and aluminum.
Of all tungsten alloys, tungsten-containing steels have acquired the greatest importance. They are resistant to abrasion, do not crack, and remain hard up to red-hot temperatures. Tools made from them not only allow you to dramatically intensify metalworking processes (the processing speed of metal products increases by 10-15 times), but also last much longer than the same tool made from other steel.
Tungsten alloys are not only heat-resistant, but also heat-resistant. They do not corrode at high temperatures under the influence of air, moisture and various chemical reagents. In particular, 10% tungsten introduced into nickel is enough to increase the corrosion resistance of the latter by 12 times! And tungsten carbides with the addition of tantalum and titanium carbides, cemented with cobalt, are resistant to the action of many acids - nitric, sulfuric and hydrochloric - even when boiling. Only a mixture of hydrofluoric and nitric acids is dangerous to them.
Tungsten has not found practical use for a long time. It was only at the end of the 19th century that the remarkable properties of this metal began to be used in industry. Currently, about 80 percent of mined tungsten is used in tungsten steels, and about 15 percent of tungsten is used to produce hard alloys. An important area of application for pure tungsten and pure alloys made from it is the electrical industry, where it is used in the manufacture of incandescent filaments of electric lamps, for parts of radio tubes and X-ray tubes, automotive and tractor electrical equipment, electrodes for resistance, atomic-hydrogen and argon-arc welding, heaters for electric furnaces, etc. Tungsten compounds have found application in the production of fire-resistant, water-resistant and weighted fabrics, as catalysts in the chemical industry.
The value of tungsten is especially enhanced by its ability to form alloys with various metals: iron, nickel, chromium, cobalt, molybdenum, which are included in steel in varying quantities. Tungsten, added in small quantities to steel, reacts with the harmful impurities of sulfur, phosphorus, and arsenic contained in it and neutralizes their negative effects. As a result, steel with the addition of tungsten obtains high hardness, refractoriness, elasticity and resistance to acids. Everyone knows the high quality of blades made of Damascus steel, which contains several percent of tungsten impurities. Also in. In 1882, tungsten began to be used in the manufacture of bullets. Gun steel and armor-piercing shells also contain tungsten. Steel with tungsten additives is used to make durable springs for cars and railway cars, springs and critical parts of various mechanisms. Rails made from tungsten steel can withstand much greater loads and have a significantly longer service life than rails made from conventional steel. A remarkable property of steel with the addition of 918 percent tungsten is its ability to self-harden, that is, with increasing loads and temperature, 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 made from it made it possible at one time to increase the processing speed of parts on metal-cutting machines several times.
And yet, tools made from high-speed steel are 35 times slower than tools made from carbide alloys. These include compounds of tungsten with carbon (carbides) and boron (borides). These alloys are close in hardness to diamonds. If the conditional hardness of the hardest of all substances, diamond, is expressed as 10 points, then the hardness of tungsten carbide (vokar) is 9.8. These alloys include the well-known win alloy of carbon with tungsten and the addition of cobalt. Pobedit itself fell out of use, but this name was preserved in relation to a whole group of hard alloys. In the mechanical engineering industry, dies for forging presses are also made from hard alloys. They wear out about a thousand times slower than steel ones.
A particularly important and interesting area of application for tungsten is the manufacture of filaments (filaments) of electric incandescent lamps. Pure tungsten is used to make electric lamp 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 with filaments made of other metals (octium, tantalum). The light emission (luminous efficiency) of electric lamps with tungsten filament is 10 times higher than that of previously used lamps with carbon filament. The brightness of the glow, durability, efficiency in energy consumption, low metal costs and ease of manufacture of electric lamps with tungsten filament have ensured their 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 the tungsten filament from the end part of the cathode tube of his design continued even after the electrodes were disconnected from the battery. This amazed his contemporaries so much that R. Wood began to be called a sorcerer. Research has shown that thermal dissociation of hydrogen molecules occurs around a heated tungsten filament; they disintegrate into individual atoms. After turning off the power, the hydrogen atoms recombine into molecules, and this releases a large amount of thermal energy, enough to heat a thin tungsten filament and cause it to glow. Based on this effect, a new type of atomic-hydrogen welding of metals was developed, which made it possible to weld various steels, aluminum, copper, brass in thin sheets, obtaining a clean and even seam. Metal 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 very resistant to acids and alkalis, is used to make meshes for various filters. Tungsten has also found application as a catalyst; it helps change the rate of chemical reactions in a technological process. A group of tungsten compounds is used in industry and laboratory conditions as reagents for the determination of protein and other organic and inorganic compounds.
Tungsten compounds are also used in the printing industry as paints (saffron, tungsten blue, tungsten yellow). Pyrotechnicians add tungsten compounds to combustible mixtures and produce multi-colored lights from rockets and fireworks. Light printing uses paper treated with sodium tungsten. In the textile industry, the salt of tungstic acid, sodium tungstate, is used to etch fabrics during dyeing. Such fabrics are waterproof and not afraid of fire. Wood also becomes fire resistant if treated with this substance.
Tungsten ditelluride WTe 2 is used to convert thermal energy into electrical energy (thermo-emf about 57 μV/K).
The coefficient of thermal expansion of tungsten is close to that of silicon, so silicon crystals of powerful transistors are soldered onto tungsten substrates to avoid cracking of these crystals when heated.
Even an incomplete list of the uses of tungsten and its compounds in industry gives an idea of the high value of this element. Now it is difficult to imagine how any of us could manage even in everyday life without tungsten. And of course, the possibilities of its use will continue to emerge.
Almost the entire world tungsten industry during the First World War was concentrated in Germany. But the raw materials for it, tungsten concentrates, were supplied from other countries. Therefore, isolated from suppliers of raw materials, the Germans were forced to process the slag accumulated near the tin smelters (remember the “wolfsfoam”!) and obtained from them about 100 tons of tungsten per year.
At the same time, the military industry's need for tungsten caused a "tungsten rush" in many countries. In Russia, the Urals and Transbaikalia became suppliers of tungsten ores. Trying to profit from the “tungsten rush,” entrepreneurs did not really take into account the interests of the state. Thus, industrialist Tolmachev, who owned the Transbaikalian fields of Bukuka and Olandu, decided to lease them to a Swedish company. And only the timely intervention of the Geological Committee prevented this. During wartime conditions, the mines of this businessman were requisitioned.
The artificial radionuclide 185 W is used as a radioactive tracer in substance research. Stable 184 W is used as a component of alloys with uranium-235 used in solid-phase nuclear rocket engines, since it is the only common tungsten isotope that has a low thermal neutron capture cross section (about 2 barn).
Before the outbreak of the First World War in 1913, the world produced 8,123 tons of tungsten concentrate (containing 60 percent tungsten trioxide). Before World War II, its production increased rapidly and in 1940 amounted to 44,013 tons (excluding the Soviet Union). According to the US Bureau of Mines, in 1972, global tungsten production was about 38,400 tons.
Applications of tungsten alloysTungsten alloys have many remarkable properties. The so-called heavy metal (from tungsten, nickel and copper) is used to make containers in which radioactive substances are stored. Its protective effect is 40% higher than that of lead. This alloy is also used in radiotherapy, since it provides sufficient protection with a relatively small screen thickness.
An alloy of tungsten carbide with 16% cobalt is so hard that it can partially replace diamond when drilling wells.
Tungsten-copper-silver pseudo-alloys are excellent materials for switches and high-voltage electrical switches: they last six times longer than conventional copper contacts.
The use of tungsten in electric lamp strands was discussed at the beginning of the article. The indispensability of tungsten in this area is explained not only by its refractoriness, but also by its ductility. From one kilogram of tungsten a wire 3.5 km long is drawn, i.e. This kilogram is enough to make the filaments of 23 thousand 60-watt light bulbs. It is thanks to this property that the global electrical industry consumes only about 100 tons of tungsten per year.
In recent years, chemical compounds of tungsten have acquired important practical importance. In particular, phosphotungstic heteropolyacid is used for the production of varnishes and bright, light-resistant paints. A solution of sodium tungstate Na 2 WO 4 gives fabrics fire resistance and water resistance, and tungstates of alkaline earth metals, cadmium and rare earth elements are used in the manufacture of lasers and luminous paints.