Tungsten is what? The degree of oxidation of tungsten. Sphere of application of tungsten

Tungsten is a chemical element whose atomic number is 74. This heavy metal is from gray-steel 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 makes it possible to use it as a catalyst. Exceptional hardness makes it suitable for use in "high-speed steel", which allows cutting materials at a higher speed than carbon steels, and in high-temperature alloys. Tungsten carbide, the connection of the element with carbon, is one of the hardest known substances and is used for making milling and turning tools. Calcium and magnesium tungstates are widely used in fluorescent lamps, and tungsten oxides are used in paints and ceramic glazes.

History of the discovery

The assumption of the existence of this chemical element was first expressed in 1779 by Peter Woolf, when he investigated the mineral wolframite and came to the conclusion that he must contain a new substance. In 1781 Karl Wilhelm Scheele established that a new acid can be obtained from tungstenite. Scheele and Thorburn Bergman proposed to consider the possibility of obtaining a new metal by reconstituting this acid, called tungsten. In 1783 two brothers, Jose and Fausto Elguyar, were found in tungsten acid, which was identical to tungsten. In the same year, the brothers managed to extract tungsten from it, using charcoal.

During the Second World War this chemical element played a huge role. The stability 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 belligerents exerted pressure on Portugal as the main source of wolframite in Europe.

Being in nature

In nature, the element is found in tungsten (FeWO ₄ / MnWO ₄ ), scheelite (CaWO ₄ ), ferret and guebnerite. Important deposits of these minerals have been found in the USA in California and Colorado, in Bolivia, China, South Korea, Russia and Portugal. In China, about 75% of world production of tungsten is concentrated. The metal is produced 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. At the moment, their development is not economically profitable. At the current level of consumption, these reserves will last only 140 years. Another valuable source of tungsten is the recycling of scrap metal.

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 stretched.

Tungsten is a chemical element whose melting point is the highest among all metals (3422 ° C). Also, it has the lowest vapor pressure. The tensile strength at T> 1650 ° C is also the largest. The element is extremely resistant to corrosion and only slightly susceptible to mineral acids. Upon contact with air, a protective oxide layer is formed on the metal surface, but completely tungsten oxidizes at high temperature. When it is added in small amounts to steel, its hardness increases dramatically.

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 decay into hafnium-72 with the emission of alpha particles (corresponding to helium-4 nuclei). Alpha decay is observed only in ¹⁸⁰ W, the lightest and sparse of these isotopes. On average, in 1 g of natural tungsten, two alpha decays of ¹⁸⁰ W per year occur.

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 a day, 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 of tungsten, the degree of oxidation varies from +2 to +6, of which +6 is the most common. The 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 plastic (can be pulled into the wire), it is widely used as filaments of incandescent lamps and vacuum lamps, 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 shielding gas.

Extremely hard tungsten is the ideal component of heavy weapon alloys. A large 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 material. In the turbine blades, wear-resistant parts and coatings, "superalloys" containing tungsten are used. These are high-temperature, 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 a glass-to-metal seal. Composites containing tungsten are an excellent substitute for lead in bullets and shot. In alloys with nickel, iron or cobalt, impact shells are made from it. Like a bullet, its kinetic energy is used to defeat the target. In the integrated circuits of tungsten make connections with transistors. Some types of strings for musical instruments are made of tungsten wire.

Using Connections

Exceptional hardness of tungsten carbide (W ₂ C, WC) makes it the most common material for making milling and turning tools. It is used in the metallurgical, mining, oil and construction industries. Tungsten carbide is also used in making jewelry, since it is hypoallergenic and is not inclined to lose its luster.

Of its oxides make the glaze. Tungsten "bronze" (called so because of the color of the oxides) are used in paints. Tungstates of magnesium and calcium 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 that can withstand 500 ° C. Some compounds containing tungsten are used as catalysts in chemistry.

Properties

The basic physical properties of W are as follows:

• Atomic number: 74.
• Atomic weight: 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 .