Tungsten - what is it? The degree of oxidation of tungsten. The scope of tungsten

Tungsten-a chemical element, atomic number of which is equal to 74. This heavy metal from steel-gray to white, featuring high strength, making it in many cases is simply irreplaceable. The melting point of he is higher than any other metal and therefore it is used as filaments in incandescent lamps and heating elements in electric furnaces (for example, alloy of zirconium-tungsten). Chemistry of the element allows it to be used as a catalyst. The exceptional hardness makes it suitable for use in “high-speed steel”, which allows you to cut materials with more speed than carbon steel, and in superalloys. Tungsten carbide, a compound of the element carbon, is one of the hardest known substances and is used for the manufacture of milling and turning tools. The tungstates of calcium and magnesium are widely used in fluorescent lamps and tungsten oxides – in paints and ceramic glazes.

History

The assumption of the existence of this chemical element was first made in 1779 by Peter wolf, when he examined the mineral wolframite and concluded that it must contain a new substance. In 1781 Carl Wilhelm Scheele found that from tungstenite can be obtained a new acid. Thorburn Scheele and Bergman suggested the possibility of obtaining a new metal by recovering this acid, called tungsteno. In 1783, two brothers, Jose and Fausto Elhuyar, found in wolframite acid, which was identical tungsteno. In the same year the brothers managed to extract the tungsten, using charcoal.

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During world war II, this chemical element has played a huge role. The resistance of the metal to high temperatures and extreme strength of its alloys done tungsten is the most important raw materials for the military industry. The warring parties have put pressure on Portugal as the main source of wolframite in Europe.

Finding in nature

In nature the element is found in wolframite (FeWO₄/MnWO₄), scheelite (CaWO₄), ferberite and hubnerite. Important deposits of these minerals are found in the U.S. in California and Colorado, Bolivia, China, South Korea, Russia and Portugal. China accounts for about 75 % of world production of tungsten. The metal is obtained by the restoration of its oxide with hydrogen or carbon.

Global reserves are estimated at 7 million t. it is Assumed that 30% of them – the deposits of wolframite and 70 % – scheelite. At this time their development is not economically profitable. At current consumption levels these reserves will only last for 140 years. Another valuable source of tungsten is the recycling of scrap metal.

Key features

Tungsten-a chemical element that is classified as a transitional metal. Its symbol W comes from the Latin word wolframium. In the periodic table, it is in the VI group between tantalum and rhenium.

Pure tungsten – it is a solid material whose color varies from steel gray to tin-white. With impurities the metal becomes fragile and tough to work with, but if not, then it can be cut with a hacksaw. In addition, it can be forging, laminating and pull.

Tungsten-a chemical element, which has a melting point is the highest among all metals (3422 °C). Also he has the lowest vapor pressure. Tensile strength at T> 1650 °C it is also the biggest. Element highly resistant to corrosion and only a little susceptible to influence of mineral acids. In contact with air on the metal surface forms a protective oxide layer, but all the tungsten is oxidized at high temperature. When adding it in small amounts in steel, its hardness increases dramatically.

Isotopes

The nature of tungsten consists of five isotopes are radioactive but have such long half-life, that they can be considered stable. All of them fall into the hafnium-72 with the emission of alpha particles (corresponding to the nuclei of helium-4). Alpha decay is only observed at the ¹⁸⁰W, the most easy and few of these isotopes. On average, 1 gram of natural tungsten per year there are two alpha-decay of ¹⁸⁰W.

In addition, as described 27 artificial radioisotopes of tungsten. The most stable of them is ¹⁸¹W with a half-life of 121.2. ¹⁸⁵W (75.1 day), ¹⁸⁸W (69,4 days) and ¹⁷⁸W (21.6 days). All other artificial isotopes half-life is less than a day, and most of them – less than 8 min. Tungsten also has four ‘meta-stable" condition, of which the most sustainable – ^179mW (6,4 min).

Connections

In chemical compounds tungsten oxidation state changes from +2 to +6, of which the most common is +6. The item generally comes into contact with oxygen, forming the yellow trioxide (WO₃), which is soluble in aqueous alkaline solutions to form tungstate ions (WO₄²⁻).

Usage

Since tungsten has a very high melting point andductile (can be stretched into wire), it is widely used as filaments of incandescent lamps and vacuum tubes, the heating elements of electric furnaces. In addition, the material can withstand extreme conditions. One of its known applications-arc welding with tungsten electrode in a protective gas.

The extremely hard tungsten – is a popular component of heavy weapons alloys. The greater density of used weights, counterweights, and ballast keels for yachts, as well as Darts (80–97 %). High-speed steel, which can cut material at higher speeds than carbon contains 18% of this substance. In turbine blades, wear-resistant parts and coatings are used "superalloys", containing tungsten. It is highly resistant heat-resistant alloys that operate at elevated temperatures.

Thermal expansion of a chemical element like borosilicate glass, so it is used for the manufacture of sealing glass to metal. Composites containing tungsten, – this is a great substitute for lead in bullets and shot. In alloys with Nickel, iron or cobalt from the shells impact. Like the bullet hitting the target uses its kinetic energy. In integrated circuits tungsten make connections with the transistors. Some types of strings for musical instruments are made from tungsten wire.

Using joins

The extreme hardness of tungsten carbide (W₂C, WC) is the most common material for the manufacture of milling and turning tools. It applies in the metallurgical, mining, petroleum and construction industries. Tungsten carbide is also used when creating jewelry as it is hypoallergenic and not prone to lose its luster.

From its oxides make a glaze. Tungsten “bronze” (so called because of the color of the oxides) are used in paints. The tungstates of magnesium and calcium are used in fluorescent lamps. Crystal tungstate serves as a scintillation detector in nuclear medicine and physics. Salts find application in the chemical and tanning industries. Tungsten disulfide is a high temperature grease to withstand 500 °C. Some of the compounds containing tungsten are used in chemistry as catalysts.

Properties

The Main physical properties of W the following:

• Atomic number: 74.
• Atomic weight: 183,85.
• Melting point: 3410 °C.
• Boiling Point: 5660 °C.
• Density: 19.3 g/cm³ at 20 °C.
• The state of oxidation: +2, +3, +4, +5, +6.
• Electronic configuration: [Xe]4F¹⁴5D⁴And 6S².