The rolled tungsten
Tungsten is a chemical element denoted by the symbol W, of the 6th group of the periodic system of elements, the atomic weight 183,92, density 19.3 g/cm3. Belongs to the group of rare metals, its share in the lithosphere of about 0,0055%. Is a light gray metal that looks like steel.
European metallurgists of the XVII century were familiar scheelite, wolframite — the most common tungsten minerals. But pure tungsten has been allocated only to the end of the eighteenth century, although for a long time remained a laboratory rarity as long as Oxland in 1847 did not patent the receipt of tungstate of sodium from the cassiterite (tin stone). He, ten years later patented the production of iron-tungsten alloys, which became the basis of modern high speed steels. But another 40 years because of the high cost to implement these developments failed. Russian tungsten steel was first smelted in the Urals in 1865 To the end of the NINETEENTH century an urgent need in the tool stainless steels, led to the start of the production line of high speed steel «Bethlehem Steel». Samples of these alloys in 1900 at the Paris world exhibition, was struck by the almost all metallurgists developed countries. A proposal to use Edison tungsten filament for incandescent lamps marked the beginning of modern electrical engineering.
The main advantages of tungsten alloy are strength, hardness, significant melting point. Many metals after holding at t° red heat and cooling in air lose their hardness, but tungsten alloys — no. This quality is called the red hardness. Alloy tungsten tool steel makes possible the most intense metal at a rate of tens of meters per second. This metal is due to refractoriness (t° melting = 3395 + 15°C), is the basis for the most durable, heat-resistant alloys. Higher melting temperature has only carbon. W has a very high boiling point (5500°C), very low evaporation rate even at about 2000 °C, a significant electric resistance: higher than that of silver five times. It has excellent mechanical properties: hardness, wear resistance — despite the intense heat, the lowest thermal expansion coefficient among metals. Pure W is easily processed, but the admixture of oxygen and carbon give it all the well-known high hardness. He also has a very high modulus of compression-stretching, very high resistance to temperature creep, good thermal conductivity, high coefficient of electron emission.
|The temperature at which the obtained data the features of t°C||20°C|
|The linear thermal expansion coefficient α [1/Deg]||43x10-6|
|The density of the alloy [g/cm3]||19,3|
|Tensile strength tensile kg/mm2||35|
|Specific heat at 20 °C [kJ/(kg·deg)]||0,134|
|The thermal conductivity K [W/(m·K)]||300,173|
|Electrical resistivity R, Mhmm2/m||0,054|
It is a chemically resistant metal. He does not react to concentrated solutions of alkalis and acids up to 400 °C in oxygen for Aqua Regia, to 600 °C in hydrogen chloride, hydrogen 700 °C for ammonia to 800 °C in carbon monoxide, nitrogen boiling mercury the presence of moisture. He reacts with a mixture of nitric and hydrofluoric acids, a mixture of hydrogen peroxide and ammonia at t° red heat, and hydrogen sulfide and chlorine — about 250 °C, boiling sulfur hot Aqua Regia, nitric acid, melts nitrite, potassium chlorate and nitrate, lead dioxide, sodium nitrite, bromine, iodine, fluorine. Carbide WC is obtained by reaction with carbon at 1400 °C and oxide WO2 — by reacting with sulfur dioxide, water vapor (at t° red heat), or oxides of Mg, Th, Al, carbon dioxide (t° 1200 °C and above).
Because of its exceptional properties W poorly to treatment (rolling, drawing, forging) — only after significant heating. The drawbacks include the difficulty of obtaining it in its pure form, a large proportion (like gold). At ordinary temperatures it is hard, brittle, not enough plastic.
Electrodes, wire are the most demanded products of tungsten. Its technological plasticity is very small, but with increasing temperature — increases while maintaining high strength. That’s why hiring get hot pressure treatment. First manufactured (to rod) — using powder metallurgy to form a Fort. Next, it is heated and Raskulinecz on a rotary forging machine — out electrodes (rods) with a diameter of 2 — 3 mm, of which after drawing in hot condition to get a wire of minimum diameter.
Tape, wire demand in electronics, electrical engineering due to the low elasticity of tungsten vapors at high working temperatures of 2500 °C. refractoriness Property allows the use of W in incandescent lamps, in the manufacture of television tubes and other vacuum tubes, for example, targets for x-ray tubes. Wire is made by winding heating elements for high temperature furnaces operating in a vacuum, hydrogen atmosphere, inert gas when heated to 3000 °C. the Rods are used as fireproof electrodes and contacts for automotive distributor.
Made from W crucibles designed for evaporation of metals. The heaviness makes it suitable for armor-piercing core bullets, cores and balances swept feathered armor-piercing and sub-caliber artillery shells, high-speed rotors gyroscopes that stabilize the flight of a ballistic missile.
Necessary for the production of tank armor, high-temperature parts of engines of space rockets, shells, shells, torpedoes, containers for storage of radioactive isotopes. Surgical instruments are made from alloy amalloy. With the help of tungsten lagerbuchse best brands of heat-resistant tool steels. The basis of this alloy as ferrotungsten (W 70−86%, Fe and Mo to 7%), obtained by recovery of scheelite or wolframite concentrates.
Modern high speed steels contain W or W+Mo to 18.5%, chromium 7% and a minor amount of cobalt. Their hardness is maintained at t° 800 °C. Ordinary steel softens at 200 °C. Most are solid «stellites» is an alloy based on cobalt and additions of Cr, W, S. For example, the alloy can be «seen» (15% of cobalt, carbide WC, a small admixture of titanium carbide) is harder than 30% tungsten steel at 1100 °C. the Cutters of this alloy is capable of shooting 1.5−2 km iron filings in a minute, to quickly process «capricious» porcelain, ebonite, glass, bronze. Wear of cutters at the same time — the most insignificant.
Used in tanning and chemical industry as catalysts and pigments. Disulphide WS2 is used as the heat-resistant lubricant at t° to 500 °C. the Tungstate of calcium and magnesium are filled with fluorescent devices. Tungsten bronze, as other salts of tungsten are involved in the production of paints. Of WO3 is made of a solid electrolyte fuel-resistant elements.
Such single crystals of tungstates, like tungstates of cadmium, lead, calcium is used as scintillation detectors of ionizing radiation in medical radiology, nuclear power. Ditelluride WTe2 is used as a Converter of thermal energy into electrical energy (thermoelectric power = 57 mV/K).
185 W — an artificial isotope used as a radioactive tracer in studies of the substances. Stable 184 W with an alloy of uranium-235 is used in nuclear solid-phase boilers, as it has a narrow (about 2 barn) capture cross section for thermal neutrons.
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