Valence of tungsten. Properties and applications of tungsten

Familiarization with the article will allow you to familiarize yourself with the physical and chemical properties of tungsten, to know the features of its location in nature, the place of extraction, the history of discovery and much more.

Tungsten (W)

Tungsten is an element of the Periodic Table of DI Mendeleev, it has the seventy-fourth atomic number, corresponds to the Latin symbol W. Under normal conditions it has a gray-silver color, shines, solid. Of all the known metals, tungsten is considered to be the most refractory. Higher than in W, the melting point is only for nonmetal - carbon. Has high chemical resistance. The valence of tungsten is variable.

History of the discovery

A chemist from Sweden Karl Wilhelm Scheele in 1781, working on scheelite treatment with nitric acid, was able to extract tungsten trioxide - a "heavy stone" of yellow color. Two years later, as early as 1783, two Eluard brothers, chemists from Spain, informed the public that they were able to obtain a new metal and tungsten oxide from wolframite.

Modern USA, France and Great Britain use the name tungsten for tungsten, which translates from Swedish as "heavy stone". Originally the word wolframium denoted a mineral wolframite. Later it passed to the metal itself.

Tungsten in nature

According to Vinogradov's calculations, the clarke number of tungsten in the earth's crust is approximately 1.3 g / t. The average index in the rocks of mountain massifs, g / t: acid rocks - 1.9, averages - 1.2, main - 0.7, ultrabasic - 0.1.

The largest reserves of this metal are concentrated in China, the USA, Canada and Kazakhstan, and countries such as Bolivia, Portugal, Uzbekistan, Russia and South Korea have smaller reserves in comparison with the above-mentioned states. About 49-50 thousand tons are produced per year, 41 of them are extracted by China, the share of Russia corresponds to 3.5 tons, Kazakhstan - 0.7 and Australia - 0.5 tons.

In industry, the main role is given to wolframite and scheelite. Minerals of wolframite are most often concentrated in granitic rocks, and their average concentration corresponds to one to two percent. Most of the producing countries export tungsten. . The price of this metal is quite high and can vary depending on its brand and the type in which it is sold (from 2,172 to 6,250,560 rubles) . The main exporters of tungsten are the UK, China and Australia. It is imported in large quantities by the United States of America, Germany, England and Japan.

Methods of obtaining

Obtaining tungsten is a process consisting of several phased stages. First, trioxide WO _{3 is} recovered from the ore concentrates with the subsequent recovery process to metal powder using hydrogen at about 700 ° C. Due to the extremely high melting point, the best way to produce this metal is powder metallurgy. In the first stage, the tungsten powder is compressed, then placed in a hydrogen atmosphere and sintered at about 1200-1300 ° C. Further exposed to an electric current and accelerating the heating temperature to three thousand degrees, this process is accompanied by sintering, and the metal turns into a monolith. Subsequent production of tungsten and its purification from the obtained monolithic materials proceed under zone melting conditions. However, tungsten powder is not the only form of obtaining this metal. When obtaining W by pyrolysis from chlorides it is possible to obtain it already in metallic form, rather than in a compact and powdery one.

Chemical quality characteristics

The valence of tungsten is variable in character, from two to six. The most stable form takes at the sixth valence. The two- and trivalent forms of the compounds are unstable and have no special significance, in practice they are not applied. Tungsten is very resistant against corrosion of metals. Room temperature allows it to maintain a constant position without being corroded; After reaching the temperature of burning begins to oxidize, forming tungsten oxide (VI). It takes the second place in the series of stresses and stands behind hydrogen. Virtually nerastvorim in hydrofluoric and dilute sulfuric acid. Nitric acid and royal vodka cause the oxidation of the surface. Dissolution is possible in hydrogen peroxide.

A mixture of hydrofluoric and nitric acid dissolves the tungsten well:

2W + 4HNO ₃ + 10HF à WF ₆ + WOF ₄ + 4NO (gas evolution) + 7H ₂ O.

In the presence of oxidants can react with molten alkali:

2W + 4NaOH ₃ + 3O ₂ à 2Na ₂ WO ₄ + 2H ₂ O.

The above examples of reactions proceed very slowly, but after reaching a temperature of 400 ° C, tungsten is self-heating and the reaction process accelerates, simultaneously generating a large amount of heat. Reactions involving oxygen require reaching a mark of 500 ° C in order for the metal to begin to heat itself.

Dissolution in a mixture of hydrofluoric and nitric acids leads to the formation of hexafluorotungstic acid - H ₂ [WF ₆ ]. Of all known tungsten compounds, the most important are tungsten anhydride or tungsten trioxide, tungstate, a peroxide compound with Me ₂ WO _X , substances formed with S, C and elements of the halogen group.

Properties of a physical nature

Tungsten is a light gray shiny metal. The temperature of tungsten during melting and boiling reaches the highest levels of Celsius in comparison with other metals. There is an assumption that the syborgy has even greater temperatures of melting and boiling, but because it "lives" very little, this can not be asserted with certainty, since this has not been proved experimentally. The tungsten melts at 3695 K, but boils, reaching 5828 K. The pure W in density is close to gold - 19.25 grams per centimeter cubic. He is characterized by paramagnetic qualities. In accordance with the Brinell measurement parameters, the hardness is 488 kg / mm ² . At twenty degrees Celsius has an UES of 55 * 10 ^-9 Ohm * m, and at a temperature of 2700 ° C the indicator of the power plant increases to 904 * 10 ^-9 Ohm * m. The sound reflected from the tungsten moves at a speed of 4290 m / s.

One of the heaviest metals with a high hardness index and a huge melting point is rightly tungsten. Properties that are inherent in it, determine its value in the world market and allow widespread use. The ability to withstand high temperatures allows large-scale application of tungsten. Wire, sheets and much more allow the creation of mechanisms that serve for many years. Externally similar to platinum. In its pure form, when heated to 1600 ° C, it can be well forged.

The use of pure metal

The main method of using tungsten is the base as a refractory material in the metallurgical industry.

Plastic and refractory properties - this is what is famous for tungsten. A wire made of this metal is indispensable in devices designed for lighting. Kinescopes and other tubes with vacuum are also widely used W.

Argon arc welding can not do without electrodes made with the participation of tungsten. Vacuum resistance furnaces also use it as a heating element, and an alloy of this metal with rhenium is used as a thermocouple.

Its high density allows it to be used as a basis for heavy-weight alloys used as a counterweight, armor-piercing core for a sub-caliber and arrow-shaped projectile shell, a core for armor-piercing cartridges and even gyroscopes that stabilize the flight of a ballistic missile.

Tungsten can serve as an excellent remedy for radiation of ionizing type. Although it has a high density, especially in comparison with traditional lead, in weight, with an equal level of protection, clothes or appliances with its use come out easier. The properties of refractoriness and hardness complicate the processing process, and therefore more often in such cases use alloys of tungsten and nickel, as well as iron, copper and other metals.

In industry, tungsten is used to create a variety of strong products. Sheet, tungsten powder, electrodes and barbell - one of the most common forms of output from W.

Application of compounds

Mechanical processing of a variety of metals, as well as materials that form part of non-metallic engineering structures, the process of drilling a well and the mining industry use strong alloys and composite materials based on tungsten carbide, titanium carbide mixtures, tantalum carbide and tungsten carbide. Tungsten grades made from these materials are divided into T30K4, T5K10, VK25, VK8, VK15, T15K4, VK2, VK6 and VK4. The brands of the TT group are used only for very complex processing in conditions of increased complexity. A striking example is the shock-rotary process of drilling a durable material with a perforator or the manufacture of forgings from steel with high heat resistance. W is used as an alloying element for steel and in alloys based on iron. "High-speed" steel with lettering marking starting with P, in more than 90% of cases, contains a share of tungsten.

Sometimes various compounds of tungsten are used as catalysts or pigments, high-temperature lubricant, for the conversion of the thermal form of energy into electrical energy.

Tungsten and Biology

Tungsten is not considered a significant metal in biology, but some bacteria and arhebacteria in their enzymes have this component located in the active center. Near the deep-water sources of the hydrothermal type, there are archebacteria-hyperthermophiles, which are considered obligate-dependent on tungsten. The presence of this metal in the enzymatic composition is considered as an archaean relic of the early period, in other words, it can allow one to assume that the early occurrence of life on earth took place with the participation of W.

Like the predominant part of other metals, the dust of tungsten causes irritation of the respiratory system.

Forms of isotopes

¹⁸² W (26,41 %), ¹⁸³ W (14,4 %), ¹⁸⁴ W (30,64 %) и ¹⁸⁶ W (28,41 %) . Tungsten of natural origin includes a mixture of five different forms of isotopes, namely ¹⁸⁰ W (0.135 wt%), ¹⁸² W (26.41%), ¹⁸³ W (14.4%), ¹⁸⁴ W (30.64%) And ¹⁸⁶ W (28.41%) . The valence of tungsten is variable and always corresponds to a number from 2 to 6 in any isotope form.

By 2016, thirty-six man-made artificial forms of identified tungsten radionuclides with mass numbers have been known: 157 ... 179, 181, 185, 187 ... 197. The radioactivity of tungsten of natural origin was discovered in 2003, but its value is extremely small, which corresponds approximately Two decays per gram per year, and the condition of this decay is the α-activity of the metal.

Finally

The most refractory of the currently existing metals is tungsten. Properties inherent in it, can find their place in a wide range of human industrial activities, starting with engineering and ending with protection from exposure. The metal was opened, roughly speaking, twice, with a difference of two years, but neither Scheele nor the Eluard brothers particularly deserved credit for his discovery. The valence of tungsten is variable and takes a value from two to six, but, as mentioned earlier, the most stable form has a sixth valence. Very resistant to corrosion, can react with alkalis and dissolve in a mixture of hydrofluoric and nitric acids.

Tungsten grades are divided into a large number of species in accordance with the method of execution, the form in which the metal is located, and the area of its application. There are many forms of its isotope, and the element in nature has a weakly expressed radioactive property and extremely slowly decays. The basis for a lot of parts and spare parts, the most diverse equipment and equipment used by man, is precisely tungsten. The price even for a kilogram of metal is quite high, but nevertheless it does not reduce the demand for it, because its qualities correspond to the cost that it is asked for.