Tungsten alloys
Characteristics
Tungsten - translated from German as "wolfsbane", element of group VI of the table of
| W atomic number. | Atomic (molar) mass g/mol | Oxidation state | Density [g/cm3] | Melting point t°C | Boiling point t°C | Melting point kJ/kg |
|---|---|---|---|---|---|---|
| № 74 | 183,84 | 0, 2, 3, 4, 5, 6 | 19,25 | 3422°С | 5500°С | 191 |
Advantages
Tungsten has a melting point of 3395 °C. Only carbon has a higher melting point. Due to its refractoriness this metal has become the basis for the most heat-resistant alloys. W boils at t° > 5500 ° C, has a minimum evaporation rate at t ° 1500 - 2500 ° C and a significant electrical resistance: almost 3 times higher than that of copper. Tungsten has excellent mechanical properties: abrasion resistance, hardness under severe heat, minimal thermal expansion coefficient and redshift resistance. This means that tungsten steels retain their hardness and strength at high temperatures in contrast to most steels, which lose their hardness after reaching t° red heat and cooling in air. Tool tungsten steel is used for metalworking at tens of meters per second. Chemically pure W is quite ductile and only an admixture of carbon and oxygen give it a certain hardness. It has a very high temperature creep resistance, high compression and tensile modulus, excellent thermal conductivity and a high electron emission coefficient, which increases even more when alloyed with other metal oxides. Today, tungsten has taken a firm place in everyday life. It can be bought at the most reasonable prices.
Chemical Properties
Tungsten is chemically resistant in contact with moisture, concentrated solutions of alkali and acids, aqua regia, hydrogen, O2 (to 400 ° C), hydrogen chloride (to 600 ° C), NH3 (to 700 ° C), boiling mercury, N2 and CO (to 800 ° C). W reacts with NH3 + H2 O2, a mixture of hydrofluoric and nitric acids, with boiling sulphur and chlorine (over 250°C), with H2 S, at t° red glow, with hot HNO3 and hot aqua regia, with melts of chlorate, potassium nitrite and nitrate, sodium nitrite, lead dioxide, bromine, fluorine, iodine. WC carbide is obtained by interaction with carbon above 1400 ° C, the oxide - by interaction with water vapor and SO2 (at t ° red glow),CO2 (above 1200 ° C), oxides of Mg, Al, Th.
Disadvantages of tungsten
It is difficult to receive in its pure form, brittleness at standard temperature, high specific weight, rigidity, low plasticity. Tungsten can be forged, rolled and drawn only if it is strongly heated.
Rolled steel production
The technological plasticity of this metal is not enough, but it improves as the temperature rises. Therefore, tungsten rolls are produced by hot working under pressure. Billet (to obtain bars or wires), the so-called stack, is formed by methods of powder metallurgy. It is then heated and forged on a rotary forging machine to bars of Ø 2 - 3 mm. They are supplied in straight sections or coiled. After hot drawing they are processed into thin wire in accordance with
Application
- Wire and tape are in demand in electrical engineering and electronics due to the low elasticity of tungsten vapor at high operating temperatures up to 2500 °C. The refractoriness makes the metal indispensable in incandescent lamps, kinescopes and other vacuum tubes such as X-ray tube targets.
- These wires are used for the winding of heating elements and for the insulation of high-temperature electric furnaces operating in vacuum or under hydrogen or inert gas atmosphere at t° up to 3000 °C.
- The rods are used as incombustible electrodes.
- Tungsten is used to make crucibles for evaporation of metals.
- W is used in the contacts of automobile ignition distributors.
- Due to its heavy weight, it is used to make counterweights for armor-piercing and cores of sub-caliber and arrow-shaped finned artillery shells, armor-piercing cores of bullets, super high-speed (160 thousand rpm) rotors of ballistic missile flight stabilizing gyroscopes.
Tungsten alloys
- Production of tank armor, torpedo and shell casings, heat-resistant parts of aircraft and space rocket engines, and containers for storing radioactive isotopes.
- Amaloy alloy is used to make surgical instruments.
- Alloying of tool and heat-resistant steels. Ferrovolfram (70-86% W, up to 7% Mo and Fe) for such alloys is obtained by the reduction of scheelite or wolframite concentrates. The best high-speed steels retain their hardness at.800°C. They contain up to 18.5% W (or W+Mo), 7% Cr and small amounts of Co. Hastalloy is a stainless nickel alloy alloy alloyed with tungsten. Even harder "stellites" are cobalt-based alloys with the addition of W, Cr, C. The hardest are tungsten carbides. Alloy "Vidna" (WC + 15% Co and a small admixture of titanium carbide) is 30% harder than the usual tungsten steel even at 1100°C. Cutters made of this alloy remove up to 2 kilometers of iron chips for a minute, can process "capricious" ebonite, glass, porcelain while wearing themselves insignificantly. "Pobedit" - consists of WC carbide crystals in a cobalt matrix - a very hard alloy, contains 80-87% W, up to 16% Co, 5-7% carbon. Titanium carbide as a filler can be used instead of tungsten carbide in superhard alloys - cermets.
- "Pobedit" is indispensable for machining metals and nonmetals by turning, milling, drilling, chiselling. It is represented by such grades as: BK2, BK4, BK6, BK8, BK15, BK25, T5K10, T15K6, T30K4 as well as WC, TiC, TaC alloys (TT grades for particularly difficult processing conditions: planing and chiselling of forgings of heat-resistant steels, perforating percussive and rotary drilling in mining and oil-producing industry).
- For the production of thermocouples tungsten-rhenium wire with 5% of rhenium and wire with 20% of rhenium (BP 5/20) are used.
Wires of VA, BM, VRN, VT-7, VT-10 and VT-15 grades are used according to
- Depending on the diameter and the surface condition, VA grade wire is used for filaments of incandescent lamps, spiral and non-spiral cathodes, grids, springs and loop heaters of electronic devices, springs of semiconductor devices.
- BPH wire is used to make bushings, traverses and those parts of devices that do not require the use of tungsten alloys.
Tungsten Salts
- These salts are used in the chemical and tanning industry as catalysts and pigments.
- Tungsten disulfide is used as a heat-resistant lubricant at t° up to 500 °C.
- Tungsten bronze and other tungsten salts are used to make paints.
- Magnesium and calcium tungstate fill fluorescent devices.
- WO3 is used to make a solid electrolyte for heat-resistant fuel cells.
- Monocrystals of tungstate (lead, cadmium, calcium tungstate) are used as scintillation detectors of ionizing radiation in nuclear power and medical radiology.
- WTe2 diteluride tungsten is used as converter of thermal energy to electrical energy (thermal EMF about 57 μV/K).
- The artificial isotope 185W is used as a radioactive tag in the study of substances. In alloy with uranium-235 stable 184W is used in solid-phase nuclear boilers, because it has a narrow thermal neutron capture cross-section (about 2 barns).
At Evek GmbH "at a discount.
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