Familiarization with the article will allow you to get acquainted with the physical and chemical properties of tungsten, find out the features of its presence in nature, the place of extraction, the history of discovery and much more.
Tungsten (W)
Tungsten is an element of the periodic table of D. I. Mendeleev, has a seventy-fourth atomic number, corresponds to the Latin symbol W. Under ordinary conditions, it has a gray-silver color, glistens, and is solid. Of all the known metals, tungsten is considered the most refractory. Higher than W, the melting point of only non-metal - carbon. It has high chemical resistance. Tungsten valency is variable.
Discovery story
A chemist from Sweden, Karl Wilhelm Scheele, in 1781, engaged in the treatment of scheelite with nitric acid, was able to produce tungsten trioxide - the "heavy stone" of yellow color. Two years later, already in 1783, the two brothers Eluard, chemists from Spain, informed the public that they were able to get new metal from tungsten and its oxide - tungsten.
Modern USA, France and Great Britain use the name tungsten for tungsten, which translates from Swedish as "heavy stone". Initially, the word wolframium denoted the 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 content in mountain rocks, g / t: acidic rocks - 1.9, medium - 1.2, basic - 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 aforementioned states. About 49-50 thousand tons are produced per year, of which 41 are produced by China, the share of Russia corresponds to 3.5 tons, Kazakhstan - 0.7 and Australia - 0.5 tons.
In industry, the main roles are given to tungsten and scheelite. Tungsten minerals are most often concentrated in granite rocks, and their average concentration corresponds to one to two percent. Most mining 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 2172 to 6,250,560 rubles) . The main exporters of tungsten are South Kazakhstan, China and Australia. The United States, Germany, England and Japan import it in large quantities.
Production methods
Obtaining tungsten is a process consisting of several stages. First, WO 3 trioxide is isolated from ore concentrates followed by a reduction process to a metal powder with hydrogen under conditions of about 700 ° C. Due to the extremely high melting point, the best way to obtain this metal is by means of powder metallurgy. In the first stage, tungsten powder is pressed, then placed in a hydrogen atmosphere and sintered under conditions of about 1200-1300 ° C. Then they are exposed to electric current and the heating temperature is accelerated 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 conditions of zone melting. However, tungsten powder is not the only form of obtaining this metal. When W is produced by pyrolysis from chlorides, it can already be obtained in metallic form, and not in compact and powder form.
Chemical quality characteristics
Tungsten valency is variable, from two to six. It takes the most stable form at the sixth valency. The bivalent and trivalent forms of the compounds are unstable and do not have special significance; they are not used in practice. Tungsten is very resistant to metal corrosion. Room temperature allows him to maintain a constant position without corrosion; upon reaching the temperature, the heat starts to oxidize, forming tungsten oxide (VI). It takes the second place in the series of voltages and follows hydrogen. It is practically insoluble in hydrofluoric and dilute sulfuric acid. Nitric acid and aqua regia cause a surface oxidation process. Dissolution is possible in hydrogen peroxide.
A mixture of hydrofluoric and nitric acid dissolves tungsten well:
2W + 4HNO 3 + 10HF à WF 6 + WOF 4 + 4NO (gas evolution) + 7H 2 O.
In the presence of oxidizing agents, it 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 when they reach 400 ° C, tungsten self-heats up and the reaction process accelerates, simultaneously generating a large amount of heat. Reactions with the participation of oxygen require reaching a mark of 500 ° C, so that the metal begins to heat up on its own.
Dissolution in a mixture of hydrofluoric and nitric acids leads to the formation of hexafluorotungsten 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.
Physical properties
Tungsten is a light gray shiny metal. The temperature of tungsten during melting and boiling reaches the highest marks in Celsius in comparison with other metals. There is an assumption that siborgium has even higher melting and boiling points, but due to the fact that it "lives" very little, this cannot be confirmed with certainty, since this has not been experimentally proven. Tungsten begins to melt at 3695 K, and boils, reaching the level of 5828 K. Pure W is close in density to gold - 19.25 grams per centimeter cubic. Paramagnetic qualities are characteristic of it. According to the Brinell measurement parameters, the hardness is 488 kg / mm 2 . At twenty degrees Celsius it has a resistivity of 55 * 10 -9 Ohm * m, and at a temperature of 2700 ° C, the resistivity index increases to 904 * 10 -9 Ohm * m. The sound reflected from tungsten moves at a speed of 4290 m / s.
One of the heaviest metals with a high hardness and a huge melting point is considered to be tungsten. The properties that are inherent in it determine its value in the world market and allow it to be widely used. The ability to withstand high temperatures allows the widespread use of tungsten. Wire, sheets and much more allow you to create mechanisms that serve for many years. Outwardly similar to platinum. In its pure form, it can be forged well when heated to 1600 ° C.
Pure metal application
The main method of using tungsten is the basis as a refractory material in the metallurgical industry.
Plastic and refractory properties are what tungsten is famous for. The wire of this metal is indispensable in devices designed for lighting. Picture tubes and other vacuum tubes are also widely used by W.
Argon-arc welding cannot do without electrodes made with tungsten. Vacuum resistance furnaces also use it as a heating element, and the alloy of this metal with rhenium is used as a thermocouple.
High density allows it to be used as a basis for heavy alloys used as a counterweight, an armor-piercing core for a sub-caliber and arrow-shaped shell of an artillery gun, a core for armor-piercing cartridges and even gyroscopes stabilizing the flight of a ballistic missile.
Tungsten can be an excellent remedy for radiation of the ionizing type. Although it has a high density, especially in comparison with traditional lead, by weight with an equal level of protection, clothes or devices with its use come out easier. The properties of refractoriness and hardness complicate the processing process, and therefore more often in such cases they use alloys of tungsten and nickel, as well as iron, copper and other metals.
In industry, tungsten is used to create a variety of durable products. Sheet, tungsten powder, electrodes and stick are one of the most common forms of production from W.
Use of compounds
The mechanical treatment of a variety of metals, as well as materials that are part of non-metallic engineering structures, well drilling and mining use durable alloys and composite materials based on tungsten carbide, a mixture of
titanium carbide, tantalum carbide and tungsten carbide. Tungsten grades made from these materials are divided into T30K4, T5K10, VK25, VK8, VK 15, T15K4, VK2, VK6 and VK4. Brands of the TT group are used only for very complex processing in conditions of increased complexity. A striking example is the rotary shock process of drilling strong 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 letter marking starting with P in more than 90% of cases contains a fraction of tungsten.
Sometimes various tungsten compounds are used as catalysts or pigments, high-temperature lubricants, for the conversion of thermal energy into electrical energy.
Tungsten and biology
Tungsten is not considered a significant metal in biology, however, some bacteria and archaebacteria as part of their enzymes have this component located in the active center. Near the deep-water sources of the hydrothermal type, archebacteria-hyperthermophiles live, which are considered obligate-dependent on tungsten. The presence of this metal in the enzymatic composition is considered as a relic of the Archean of the early period, in other words, this may suggest that the early emergence of life on earth took place with the participation of W.
Like the predominant part of other metals, tungsten dust causes respiratory irritation.
Isotope Forms
Natural tungsten 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%) . Tungsten valency is variable and always corresponds to a number from 2 to 6 in any form of isotope.
By 2016, thirty-six man-made artificial forms of identified tungsten radionuclides with mass numbers were already known: 157 ... 179, 181, 185, 187 ... 197. The radioactivity of natural tungsten was discovered in 2003, but its rate is extremely small, which corresponds to approximately two decays per gram per year, and the condition for this decay is the α-activity of the metal.
Finally
The most refractory of the existing metals is tungsten. The properties inherent in it make it possible to find its place in a wide range of industrial activities of a person, starting with mechanical engineering and ending with protection against radiation. The metal was discovered, roughly speaking, twice, with a difference of two years, but neither Scheele nor the Eluard brothers claimed much credit for his discovery. Tungsten valency is variable and takes a value from two to six, but, as mentioned earlier, the most stable form has a sixth valency. Very resistant to corrosion, can react with alkalis and dissolve in a mixture of hydrofluoric and nitric acids.
Tungsten brands are divided into a huge number of types in accordance with the method of execution, the form in which the metal is located, and the scope of its application. There are many forms of its isotope, and the element itself in nature has a weakly pronounced radioactive property and decays extremely slowly. It is tungsten that serves as the basis for many parts and spare parts, the most diverse equipment and equipment used by man. The price even per kilogram of metal is quite high, but nevertheless this does not reduce the demand for it, because its qualities correspond to the cost that is being asked for.