Tungsten is a chemical element whose atomic number is 74. This heavy metal from steel-gray to white is highly durable, which makes it simply irreplaceable in many cases. 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 it to be used as a catalyst. Its exceptional hardness makes it suitable for use in "high speed steels" which allow materials to be cut at higher speeds than carbon steels and in high temperature alloys. Tungsten carbide, a compound of the element with carbon, is one of the hardest substances known and is used to make milling and turning tools. Calcium and magnesium tungstates are widely used in fluorescent lamps, and tungsten oxides are widely used in paints and ceramic glazes.
Discovery history
The existence of this chemical element was first suggested in 1779 by Peter Woolf, when he investigated the mineral wolframite and came tothe conclusion that it must contain a new substance. In 1781, Carl Wilhelm Scheele established that a new acid could be obtained from tungstenite. Scheele and Thorburn Bergman proposed to consider the possibility of obtaining a new metal by reducing this acid, called tungsthenic acid. In 1783, two brothers, José and Fausto Elguiar, found an acid in wolframite that was identical to tungsthenic acid. 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, has made tungsten the most important raw material for the military industry. The belligerents put pressure on Portugal as the main source of wolframite in Europe.
Being in nature
In nature, the element occurs in wolframite (FeWO4/MnWO4), scheelite (CaWO4), ferberite and hübnerite. 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. 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 are deposits of wolframite and 70% of scheelite. Currently, their development is not economically viable. At the current level of consumption, these reserves will last only 140 years. Another valuable sourcetungsten is a scrap metal recycling.
Key Features
Tungsten is a chemical element that is classified as a transition metal. Its W symbol comes from the Latin word wolframium. In the periodic table, it is in group VI between tantalum and rhenium.
In its purest form, tungsten is a hard material that ranges in color from steel gray to pewter white. With impurities, the metal becomes brittle and difficult to work with, but if there are none, then it can be cut with a hacksaw. In addition, it can be forged, rolled and drawn.
Tungsten is a chemical element whose melting point is the highest among all metals (3422 °C). It also has the lowest vapor pressure. It also has the highest tensile strength at T> 1650 °C. The element is extremely resistant to corrosion and is only slightly attacked by mineral acids. Upon contact with air, a protective oxide layer forms on the metal surface, but tungsten is completely oxidized at high temperatures. When it is added in small amounts to steel, its hardness increases dramatically.
Isotopes
In nature, tungsten is made up of five radioactive isotopes, but they have such a long half-life that they can be considered stable. All of them decay 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 theseisotopes. On average, two alpha decays occur in 1 g of natural tungsten per year 180W.
In addition, 27 artificial radioactive isotopes of tungsten have been described. The most stable of these is 181W with a half-life of 121.2 days, 185W (75.1 days), 188 W (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).
Connections
In chemical compounds, tungsten oxidation state changes from +2 to +6, of which +6 is the most common. The element typically bonds with oxygen to form yellow trioxide (WO3), which dissolves in aqueous alkaline solutions as tungstate ions (WO4 2−).
Application
Because tungsten has a very high melting point and is ductile (can be drawn into wire), it is widely used as the filament of incandescent lamps and vacuum lamps, as well as in the heating elements of electric furnaces. In addition, the material withstands extreme conditions. One of its known applications is gas-shielded tungsten arc welding.
Exceptionally hard, tungsten is an ideal component for heavy weapon alloys. High density is used in kettlebells,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 steel, contains up to 18% of this substance. Turbine blades, wear parts and coatings use "superalloys" containing tungsten. These are heat-resistant, highly resistant alloys that function at elevated temperatures.
The thermal expansion of a chemical element is similar to borosilicate glass, so it is used to make glass-to-metal seals. Composites containing tungsten are an excellent substitute for lead in bullets and shot. In alloys with nickel, iron or cob alt, impact projectiles are made from it. Like a bullet, 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 (W2C, WC) makes it the most common material for milling and turning tools. It is applied in 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) is used in paints. Magnesium and calcium tungstates are used in fluorescentlamps. Crystalline tungstate serves as a scintillation detector in nuclear medicine and physics. S alts are used in the chemical and leather industries. Tungsten disulfide is a high temperature grease that can withstand 500°C. Some compounds containing tungsten are used in chemistry as catalysts.
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/cm3 at 20°C.
- Oxidation states: +2, +3, +4, +5, +6.
- Electronic Configuration: [Xe]4 f 145 d 46 s 2.
