Tungsten is a chemical element with an atomic number of 74. This heavy metal is from steel-gray to white, characterized by high strength, which makes it in many cases simply irreplaceable. 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). The chemistry of the element allows its use as a catalyst. Its exceptional hardness makes it suitable for use in “high-speed steel”, which allows cutting materials at a higher speed than carbon steels, and in heat-resistant alloys. Tungsten carbide, a compound of an element with carbon, is one of the hardest materials known and is used for the manufacture of milling and turning tools. Calcium and magnesium tungstates are widely used in fluorescent lamps, and tungsten oxides in paints and ceramic glazes.
Discovery story
The assumption of the existence of this chemical element was first made in 1779 by Peter Wolfe, when he studied the mineral tungsten and came to the conclusion that it should contain a new substance. In 1781, Karl Wilhelm Scheele established that new acid can be obtained from tungstenite. Scheele and Thorburn Bergman proposed to consider the possibility of obtaining a new metal by reducing this acid, called tungstenic. In 1783, two brothers, Jose and Fausto Elguyar, found acid in tungsten that was identical to tungsten. In the same year, the brothers managed to isolate tungsten from it using charcoal.
During the Second World War, this chemical element played a huge role. The resistance of the metal to high temperatures, as well as the extreme strength of its alloys, made tungsten the most important raw material for the military industry. The warring parties put pressure on Portugal as the main source of tungsten in Europe.
Being in nature
In nature, the element is found in tungsten (FeWO 4 / MnWO 4 ), Scheelite (CaWO 4 ), Ferberite and Huberner. 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's tungsten production is concentrated in China. A metal is obtained by reducing its oxide with hydrogen or carbon.
World reserves are estimated at 7 million tons. It is estimated that 30% of them are tungsten deposits and 70% are scheelite. At present, their development is not economically viable. At the current level of consumption, these stocks will last only 140 years. Another valuable source of tungsten is scrap processing.
Main characteristics
Tungsten is a chemical element that is classified 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.
In its pure form, tungsten is a solid material, the color of which varies from gray-steel to tin-white. With impurities, the metal becomes brittle and difficult to work with, but if they are not, then it can be cut with a hacksaw. In addition, it can be forged, rolled and pulled.
Tungsten is a chemical element whose melting point is the highest among all metals (3422 ° C). He also has the lowest vapor pressure. The tensile strength at T> 1650 ° C is also the highest. The element is extremely resistant to corrosion and only slightly susceptible to the effects of mineral acids. Upon contact with air, a protective oxide layer forms on the metal surface, but tungsten is completely oxidized at high temperature. When it is added in small quantities to steel, its hardness increases sharply.
Isotopes
In nature, tungsten consists of five radioactive isotopes, but they have such a long half-life that they can be considered stable. All of them decompose into hafnium-72 with the emission of alpha particles (corresponding to helium-4 nuclei). Alpha decay is observed only at 180 W, the lightest and rarest of these isotopes. On average, in 1 g of natural tungsten per year, two alpha decays of 180 W.
In addition, 27 artificial radioactive isotopes of tungsten are described. The most stable of these is 181 W with a half-life of 121.2 days, 185 W (75.1 days), 188 W (69.4 days) and 178 W (21.6 days). For all other artificial isotopes, the half-life does not exceed 24 hours, and most of them are less than 8 minutes. Tungsten also has four “metastable” states, of which the most stable is 179m W (6.4 min).
Connections
In chemical compounds, tungsten oxidation state changes from +2 to +6, of which +6 is the most common. An element, as a rule, comes into contact with oxygen, forming a yellow trioxide (WO 3 ), which dissolves in aqueous alkaline solutions in the form of tungstate ions (WO 4 2− ).
Application
Since tungsten has a very high melting point and is ductile (can be extended into a wire), it is widely used as filament and vacuum lamp 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 a protective gas.
Extremely hard tungsten is an ideal component of heavy weapon alloys. High density is used in weights, balances and ballast keels for yachts, as well as in darts (80–97%). High-speed steel, which can cut material at higher speeds than carbon steel, contains up to 18% of this substance. In turbine blades, wear-resistant parts and coatings, “superalloys” containing tungsten are used. These are heat-resistant, highly resistant alloys that function at elevated temperatures.
The thermal expansion of a chemical element is similar to borosilicate glass; therefore, it is used for the manufacture of glass-metal seals. Tungsten composites are an excellent substitute for lead in bullets and shots. In alloys with nickel, iron or cobalt, shock shells are made of it. Like a pool, its kinetic energy is used to hit a target. In integrated circuits, tungsten is used to make connections to transistors. Some types of musical instrument strings are made from tungsten wire.
Using Connections
The exceptional hardness of tungsten carbide (W 2 C, WC) makes it the most common material for the manufacture of milling and turning tools. It is used in the metallurgical, mining, oil and construction industries. Tungsten carbide is also used in jewelry making, as it is hypoallergenic and does not tend to lose its luster.
Glaze is made from its oxides. Tungsten "bronze" (so called because of the color of the oxides) are used in paints. Magnesium and calcium tungstates are used in fluorescent lamps. Crystalline tungstate serves as a scintillation detector in nuclear medicine and physics. Salts are used in the chemical and leather industries. Tungsten disulfide is a high temperature grease withstanding 500 ° C. Some compounds containing tungsten are used as catalysts in chemistry.
The properties
The main physical properties of W are as follows:
- Atomic number: 74.
- Atomic mass: 183.85.
- Melting point: 3410 ° C.
- Boiling point: 5660 ° C.
- Density: 19.3 g / cm 3 at 20 ° C.
- Oxidation states: +2, +3, +4, +5, +6.
- Electronic configuration: [Xe] 4 f 14 5 d 4 6 s 2 .