Tungsten has a long and storied history dating back to the Middle Ages, when tin miners in Germany reporting finding an annoying mineral that often came along with tin ore and reduced the yield of tin during smelting. The miners nicknamed the mineral wolfram for its tendency to “devour” tin “like a wolf.”
Tungsten was first identified as an element in 1781, by the Swedish chemist Carl Wilhelm Scheele, who discovered that a new acid, which he called tungstic acid, could be made from a mineral now known as scheelite. Scheele and Torbern Bergman, a professor in Uppsala, Sweden, developed the idea of using charcoal reduction of that acid to obtain a metal.
Tungsten as we know it today was finally isolated as a metal in 1783 by two Spanish chemists, brothers Juan Jose and Fausto Elhuyar, in samples of the mineral called wolframite, which was identical to tungstic acid and which gives us tungsten’s chemical symbol (W). In the first decades after the discovery scientists explored various possible applications for the element and its compounds, but the high cost of tungsten made it still impractical for industrial use.
In 1847, an engineer named Robert Oxland was granted a patent to prepare, form, and reduce tungsten to its metallic format, making industrial applications more cost-effective and therefore, more feasible. Steels that contain tungsten began to be patented in 1858, leading to the first self-hardening steels in 1868. New forms of steels with up to 20% tungsten were displayed at the 1900 World Exhibition in Paris, France, and helped to expand the metal work and construction industries; these steel alloys are still widely used in machine shops and construction today.
In 1904, the first tungsten filament light bulbs were patented, taking the place of carbon filament lamps that were less efficient and burned out more quickly. Filaments used in incandescent light bulbs have been made from tungsten ever since, making it essential to the growth and ubiquity of modern artificial lighting.
In the tooling industry, the need for drawing dies with diamondlike hardness and maximum durability drove the development of cemented tungsten carbides in the 1920s. With the economic and industrial growth after the World War II, the market for cemented carbides used for tool materials and canst「uction parts also grew. Today, tungsten is the most widely used of the refractory metals, and it is still extracted primarily from wolframite and another mineral, scheelite, using the same basic method developed by the Elhuyar brothers.
Tungsten is often alloyed with steel to form tough metals that are stable at high temperatures and used to make products such as high-speed cuttlng tools and rocket engine nozzles, as well as the large volume application of ferro-tungsten as the prows of ships, especially ice breakers. Metallic tungsten and tungsten alloy mill products are in demand for applications in which a high-density material (19.3 g/cm3) is required, such as kinetic energy penetrators, counterweights, flywheels, and governors Other applications include radiation shields and x-ray targets.
Tungsten also forms compounds – for example, with calcium and magnesium, producing phosphorescent properties that are useful in fluorescent light bulbs. Tungsten carbide is an extremely hard compound that accounts for about 65% of tungsten consumption and is used in applications such as the tips of drill bits, high-speed cutting tools, and mining machinery Tungsten carbide is famous for its wear resistance; in fact, it can only be cut using diamond tools. Tungsten carbide also exhibits electrical and thermal conductivity, and high stability. However, it brittleness is an issue in highly stressed structural applications and led to the development of metal-bonded composites, such as the additional of cobalt to form a cemented carbide .
Commercially, tungsten and its shaped products – such as heavy alloys, copper tungsten, and electrodes – are made through pressing and sintering in near net shape. For wire and rod wrought products, tungsten is pressed and sintered, followed by swaging and repeated drawing and annealing, to produce a characteristic elongated grain structure that carries over in finished products ranging from large rods to very thin wires.
Post time: Jul-05-2019