Tungsten - chemical element, atomic numberwhich is equal to 74. This heavy metal from steel-gray to white, characterized by high strength, which makes it in many cases simply indispensable. Its melting point is higher than that of any other metal, and therefore it is used as filaments in incandescent lamps and heating elements in electric furnaces (for example, zirconium-tungsten alloy). Element chemistry allows its use as a catalyst. Exceptional hardness makes it suitable for use in “high-speed steel”, which allows cutting materials at a higher rate than carbon steels and in high-temperature alloys. Tungsten carbide, an element bonding with carbon, is one of the hardest known substances and is used to make milling and turning tools. Calcium and magnesium tungstates are widely used in fluorescent lamps, and tungsten oxides in paints and ceramic glazes.
The assumption of the existence of this chemicalThe element was first expressed in 1779 by Peter Wolfe when he explored the mineral wolframite and concluded that it must contain a new substance. In 1781, Karl Wilhelm Scheele established that a new acid could be obtained from tungsthenite. Scheele and Thorburn Bergman proposed to consider the possibility of obtaining a new metal by reducing this acid, called tungstenovoy. In 1783, two brothers, José and Fausto Elguyar, found in tungstic acid, which was identical to tungstenovoy. In the same year, the brothers managed to extract tungsten from it using charcoal.
During World War II, this chemicalelement played a huge role. The resistance of the metal to high temperatures, as well as the extreme strength of its alloys, have made tungsten the most important raw material for the military industry. The warring parties put pressure on Portugal as the main source of wolframite in Europe.
In nature, the element is found in tungsten (FeWO4/ MnWO4) scheelite (CaWO4), ferberite and hubnerite.Important deposits of these minerals are found in the USA in California and Colorado, in Bolivia, China, South Korea, Russia and Portugal. About 75% of the world production of tungsten is concentrated in China. The metal is obtained by reducing its oxide with hydrogen or carbon.
World reserves are estimated at 7 million tons.It is assumed that 30% of them - deposits of wolframite and 70% - scheelite. At this time, their development is not economically viable. With the current level of consumption of these stocks will last only 140 years. Another valuable source of tungsten is the recycling of scrap metal.
Tungsten is a chemical element thatclassified as a transition metal. Its symbol W comes from the Latin word wolframium. In the periodic table, it is in group VI between tantalum and rhenium.
Pure tungsten is a solid materialwhose color varies from gray steel to tin white. With metal impurities it becomes fragile and it is difficult to work with it, but if they are not there, then it can be cut with a hacksaw. In addition, it can be forged, rolled and pulled.
Tungsten - chemical element, temperaturemelting of which is the highest among all metals (3422 ° C). It also has the lowest vapor pressure. The tensile strength at T> 1650 ° C is also greatest. The element is extremely resistant to corrosion and only slightly exposed to mineral acids. Upon contact with air, a protective oxide layer forms on the surface of the metal, but completely tungsten is oxidized at high temperature. When it is added in small amounts to steel, its hardness increases dramatically.
In nature, tungsten consists of five radioactiveisotopes, but they have such a long half-life that they can be considered stable. All of them break up into hafnium-72 with the emission of alpha particles (corresponding to helium-4 nuclei). Alpha decay is observed only in 180W, the lightest and rarest of these isotopes. On average, two alpha decays occur in 1 g of natural tungsten per year. 180AT.
In addition, 27 artificial radioactive isotopes of tungsten are described. The most stable of them is 181W with a half-life of 121.2 days, 185W (75.1 days), 188W (69.4 days) and 178W (21.6 days).All other artificial isotopes have a half-life of less than a day, and most of them are less than 8 minutes. Tungsten also has four “metastable” states, of which the most stable is 179mW (6.4 min).
In chemical compounds, tungsten degreeoxidation varies from +2 to +6, of which the most common is +6. The element tends to bond with oxygen to form yellow trioxide (WO3), which is soluble in aqueous alkaline solutions in the form of tungstate ions (WO42−).
Since tungsten has a very highmelting point and plastic (can be drawn out into a wire), it is widely used as filament and vacuum tube filaments, as well as in heating elements of electric furnaces. In addition, the material withstands extreme conditions. One of its known applications is arc welding with a tungsten electrode in shielding gas.
Exceptionally hard tungsten is perfect.component of heavy weapon alloys. High density is used in weights, counterweights and ballast keels for yachts, as well as in darts (80–97%). High-speed steel, which can cut material at higher speeds than carbon, contains up to 18% of this substance. Turbine blades, wear-resistant parts and coatings use “superalloys” containing tungsten. These are heat-resistant high-resistant alloys, which operate at elevated temperatures.
Thermal expansion of a chemical elementborosilicate glass, so it is used for the manufacture of glass-to-metal seals. Composites containing tungsten are an excellent substitute for lead in bullets and shot. In alloys with nickel, iron or cobalt, shells of percussion are made of it. Like a bullet, its kinetic energy is used to hit a target. In tungsten integrated circuits make connections with transistors. Some types of strings for musical instruments are made from tungsten wire.
Exceptional hardness of tungsten carbide (W2C, WC) makes it the most commonmaterial for the manufacture of milling and turning tools. It is used in the metallurgical, mining, oil and construction industries. Tungsten carbide is also used to create jewelry, as it is hypoallergenic and not prone to lose its luster.
From its oxides make glaze.Tungsten "bronze" (so called because of the color of oxides) are used in paints. Magnesium and calcium tungstates are used in fluorescent lamps. Crystal tungstate serves as a scintillation detector in nuclear medicine and physics. Salts are used in the chemical and leather industry. Tungsten disulfide is a high-temperature lubricant that can withstand 500 ° C. Some compounds containing tungsten are used as catalysts in chemistry.
The basic physical properties of W are as follows:
