Chemical element, tungsten, is in the sixth group of the periodic system, has an atomic mass of 183.84. Is one of the most heavy metals. Was obtained from tungsten anhydride, by restoring its carbon. Has a light gray color with metallic luster. In nature, occurs only in mixtures with multiple stable isotopes, with mass numbers from 180 to 186.
|The atomic number of W||Atomic (molar) mass, g/mol||The degree of oxidation||Density [g/cm3]||The melting temperature t°C||The boiling point of t°C||The heat of fusion kJ/kg|
|No. 74||Of 183.84||0, 2, 3, 4, 5, 6||19,25||3422°C||5500°C||191|
Even in the 17th century, Europeans knew wolframite and scheelite — the most common tungsten minerals. Pure tungsten was made in the late eighteenth century, but long remained a laboratory rarity, until in 1847, Oxland not patented getting a tungsten acid, sodium tungstate and tungsten from cassiterite. 10 years later, Oxland patented the production of iron-tungsten alloys that formed the basis of modern high speed steels. However, almost half a century failed to implement these designs into production due to high cost. In Russia tungsten steel was first smelted in the Urals in 1865 At the end of the NINETEENTH century an acute need for alloyed and tool steels led to the launch of the line high-speed steels at the company «Bethlehem Steel». In 1900 samples of these alloys were presented at the world exhibition in Paris, hitting all of metallurgists developed countries. In the early XX century Edison had thought to use in incandescent lamps the tungsten filament. This was the beginning of the use of tungsten in electrical engineering. Today, tungsten has ceased to be a rarity and has occupied a firm place in everyday life. You can buy it at the most affordable prices.
W refers to the group of refractory metals. All the items that are in this group are characterized by high melting temperature (over 2500°K) and high density (above 8 g/m3). Along with this, tungsten has high hardness — 3430 MPa, also, this metal, in comparison with the other refractory elements in the same group of the periodic system, has the highest boiling point of 5828°K (5555°C). Among the metals of this group tungsten is one of the most expensive.
Typically, tungsten is used in two forms. The first porous metal impregnated with copper or silver. Thanks to impregnation, the metal is easier to cut at a speed which can reach 600 m/min. when compared with the second type of tungsten is ductile and alloy, the latter maximum cutting speed is 90 m/min.
In addition, tungsten alloys are divided into: single-phase and heterophase. Monophasic alloys are considered to be alloys, alloy in certain chemical elements (molybdenum, chromium, rhenium, and etc). The most stable is the alloy, which contains 15% molybdenum. The plastic alloy obtained by alloying rhenium, its percentage content in the alloy is about 26%. Regarding the price of tungsten this type, it is slightly lower compared to porous metals.
To heterophase alloys include those containing carbon and zirconium (niobium), as a percentage of 0.20 to 0.60 and 0.2 to 0.6 respectively. At temperatures below 2300 °C of these alloys is a selection of fine carbide particles, which improves the high temperature strength, these alloys are also called dispersion-strengthened.
Often alloys, which consists of carbide of WC, refers to the group B. since They are different brands (VK6, VK8, ВК6М, ВК8М). In this case, the content of tungsten carbide — cobalt. Some of the markings found in the letter M — fine-grained alloy has improved wear resistance, but because of malosernistoj lowered resistance to shocks. Alloys of group VK is used for the treatment of non-metallic materials, non-ferrous metals and their alloys, and cast iron. Buy tungsten alloy can be in any specialized outlets.
Along with this, there are still a few groups, such as TTK and TK. TTC — the composition of the alloy contained carbides of titanium and tantalum. They are used for heat resistant steels and titanium alloys.
Alloy group of TC differs from the TTC to the fact that it includes only the titanium carbide. These alloys are used when working with carbon steels, by using turning and milling.
Because of the high cost of tungsten, often used without tungsten alloys, their composition includes carbides of titanium and other refractory metals (Nickel, molybdenum, etc.)
More than 60% of the tungsten mined is used for making stainless and alloy steels, special tool steels. Often for these purposes is a scrap of tungsten. Tungsten non-consumable electrodes used for welding all types of steels AC and DC. Thanks to the special colouring of electrodes (Golden, red, blue, gray, etc.) can be distinguished for what type of alloys they are, and what kind of current you can use.
For many years heat-resistant tungsten alloys are used for heat-resistant coatings of parts of equipment. Exceptional refractoriness and minimum surface evaporation give the possibility to use this metal for the filaments of light bulbs. Some chemical companies use it as a catalyst in organic synthesis. Along with this, compounds of tungsten are used as heat-resistant grease, as dyes fabrics, enhancing water resistance and fire resistance.
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