Tungsten: The Element

Tungsten, also referred to as Wolfram, is a metallic chemical element classified under the transition metals of the periodic table and is well known for its strength and durability. Its symbol is 'W' and has an atomic number 74. Tungsten metal in the pure form is steel gray to tin white in color and can be cut by a hacksaw, spun, drawn, forged or extruded. However, in the impure form it's quite hard and brittle and quite difficult to work with. Tungsten has the highest melting point (3410° C) of all the non-alloyed metals and the second-highest melting point of all elements after Carbon. Further, at temperatures beyond (1650° C), tungsten features the highest tensile strength than that of any element.

History

In 1781, a Swedish chemist named Carl Wilhelm Scheele discovered that by using a calcium tungstate mineral called Scheelite, a new acid called Tungstic acid could be formed. Later in 1783, two Spanish chemists, Juan José and Fausto Elhuyar encountered Wolframite acid which was identical to Tungstic acid. They reduced this acid by using charcoal and were the first ones to isolate the metal tungsten from samples of the mineral Wolframite (Fe, Mn)WO₄. And this is where this element got its name. The name 'tungsten' has been derived from the Swedish word tung sten, meaning heavy metal, and is used in mostly in England and the US. However, in Germany and other European regions, this heavy metal is referred to by the name 'Wolfram' (Since the element was first isolated from the mineral wolframite).

Occurrence

The element tungsten does not occur as a free metal and occurs in the Earth's crust in the form of tungstenite, tungsten disulfide, scheelite (calcium tungstate), stolzite (lead tungstate) and wolframite. Around 20 minerals are known today which contain tungsten, however, only wolframite and scheelite are of industrial and commercial importance. It is estimated that approximately 1.5 grams of tungsten is present per ton of rock in the Earth's crust. China is reported to have 75% of the world's tungsten resources. Other significant deposits of this metal are found in Colorado, California, Russia, Portugal, Bolivia and South Korea. Today, 40,000 tonnes of tungsten is produced every year and the metal's reserves are said to have over 5 million tonnes. Tungsten can be recycled and this recycled metal serves 30% of the metal's demand.

Properties

Besides being the element with the highest melting point and highest tensile strength, some of the other properties of this metal are as follows:

• Tungsten is inert to oxygen at normal temperatures, but is seen to combine with it and form trioxides at red heat.
• Corrosion resistant and gets only slightly corroded by most of the mineral acids, except for mixtures of hydrofluoric acid and concentrated nitric acid.
• It has the lowest coefficient of linear thermal expansion, that is 4.43 × 10-6 per ° C at 20° C. Tungsten's thermal expansion is the same as that of borosilicate glass, thereby facilitating glass-metal seals.
• When attacked with fluorine at room temperature, it forms hexafluorides.
• Natural tungsten comprises five stable isotopes and 21 known unstable isotopes. The five stable isotopes are tungsten-180 (0.12 percent), tungsten-182 (26.3 percent), tungsten-183 (14.28 percent), tungsten-184 (30.7 percent), and tungsten-186 (28.6 percent).
• Tungsten consists of small amounts of carbon and oxygen, which is what gives the metal its durability and strength.

Applications of Tungsten

The most famous application of tungsten is as a filament in light bulbs. Besides this, it is also used in electric contacts, arc welding electrodes, electron and television tubes and several spacecraft and high temperature applications (since it has a high melting point). This metal is also used also for bringing about glass-metal seals due to its thermal expansion being the same as that of borosilicate glass. When used in alloys like steel (18% tungsten), tungsten employs strength to it. Further, high density alloys of tungsten are used to make darts and fishing lures. Since the density of tungsten is similar to that of gold, it can replace gold and platinum in jewelry. Tungsten rings are quite popular, since the hardness of the metal makes the ring scratch-resistant and future polishing is also not needed. Tungsten bronzes and some other tungsten compounds find their use in paints, and calcium and magnesium tungstates are used in florescent lighting. Various other salts of tungsten are used in chemical and tanning industries.

Effects of Tungsten on Health and Environment

Industrial workers who have been exposed to tungsten alone or its insoluble compounds have not shown any signs of pneumoconiosis. This metal is not known to have any chronic effects, and even prolonged exposure to tungsten has not aggravated any medical conditions by far. The acute affects of tungsten exposure can be irritation to the eyes (watering and redness) and skin irritation (reddening, itching and scaling). Inhalation of the metal particles can result in lung and mucus membrane irritation. Just as it's not known to be hazardous to human beings, similarly it's also not known to be harmful to the environment. Specific data with its eco-toxicity details are still not yet known.

Tungsten's properties make it best suited for various uses in many industries today. However, we still do not know if tungsten is really low in toxicity. Recent studies say that tungsten may not be as harmless as we have believed it to be. Though, it is always advisable to wear protective equipment while handling this metal and its compounds.