Tungsten

GENERAL CHARACTERISTICS

Tungsten — an element of the sixth group of the periodic system of the elements, where it is designated by the symbol W. the Atomic weight 183,92, specific weight 19.3 g/cm3. It is light-grey heavy metal with a steel tint. one of the rare metals. Its share in the earth’s crust less than 0,006%.

HISTORY

European metallurgists 400 years ago was familiar with the tungsten ore. Pure tungsten has managed to melt only at the end of XVIII century, but for a long time it remained a laboratory rarity, while in the middle of the XIX century was not patented getting a tungstate of sodium, based on which started to produce iron-tungsten alloys, which became the basis of modern tool steels. Because of the high cost to apply these developments in mass production was only towards the end of the NINETEENTH century, when there was a pressing need in the tool alloy steels. The first line for the production of tungsten steel was launched in the «Bethlehem Steel company». Samples of such steel in 1900 was presented at the Paris world exhibition,

CHEMICAL PROPERTIES

Tungsten inert in an oxygen atmosphere to 400 °C, hydrogen to 600 °C, ammonia to 700 °C, carbon monoxide to 800 °C, in concentrated solutions of acids, alkalis, Aqua Regia, boiling mercury. He reacts with a mixture of nitric and plasmavol acids, a mixture of hydrogen peroxide and ammonia at t° red heat, with chlorine and hydrogen sulfide at 250 °C, boiling sulfur hot Aqua Regia, nitric acid, melts of salts of alkaline earth metals, bromine, fluorine, iodine.

PHYSICAL advantages

Tungsten steels are wear resistance, hardness, high melting point, high hot hardness. Most metals upon reaching the t° red heat and cooling lose their hardness, in contrast to tungsten steels. Instrumental tungsten steel makes possible the metal with a speed of tens of meters per second. Tungsten has become one of the most durable, heat-resistant materials. It has a very high boiling point, the minimum evaporation rate, the higher the electrical resistance. It has excellent mechanical properties: minimum coefficient of thermal expansion among metals. All known hardness gives it the impurities of oxygen and carbon. Tungsten has a high modulus of tension and compression, exceptional resistance to thermal creep, good thermal conductivity, high coefficient of light output.

DISADVANTAGES

Because of the extreme refractoriness and hardness, tungsten is poorly processed — only to achieve high temperatures. The disadvantage is the complexity of mining and obtaining it in its pure form. Under normal conditions it is hard, brittle, fragile material.

PRODUCTION

The most demanded products of tungsten wire and electrodes. Under normal conditions, technological plasticity of tungsten is minimal, but with increasing temperature — increased without loss of strength. That’s why hiring get hot pressure treatment. First using powder metallurgy to form the workpiece — the so-called Fort. After heating it Raskulinecz on a rotary forging machine — out electrodes (rods) section 2 — 3 mm, of which after drawing in the hot condition pull wire minimum diameter.

USE

High operating temperature — above 2000 °C and high electron emission make the tungsten ribbon and the wire current in electronics, electrical engineering. Exceptional refractoriness allows the use of tungsten filament in electric lighting devices and vacuum tubes, targets for x-ray tubes. Wire is a coil of heating elements of electric furnaces operating in vacuum or inert gas atmosphere up to t° 3000 °C. the Rods are used as fireproof electrodes, and contacts of the ignition timing. Tungsten crucible used for evaporation of metals. Cores, balances and feathered armor-piercing projectiles, high-speed rotors gyroscopes that stabilize the flight of the missile are also produced from heavy-weight tungsten.

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