Tungsten, also referred to as Wolfram, is a metallic chemical element classified under the transition metals of the periodic table. Its symbol is 'W' and has an atomic number 74. Tungsten metal is well-known for its strength and durability, and in the pure form is steel gray to tin white in color, and is easy to work with.
However, in the impure form it's hard and brittle, and quite difficult to work with. It has the highest melting point (3410°C) of all 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.
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).
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 to 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 tons of tungsten is produced every year and the metal's reserves are said to have over 5 million tons. It can also be recycled, with the recycled metal serving 30% of the metal's demand.
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, with minimal corrosion on exposure to most 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
Its most famous application 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 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 compounds find their use in paints, and calcium and magnesium tungstates are used in fluorescent 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 effects of 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 mucous membrane irritation. Just as it is not known to be hazardous to human beings, so also it's not known to be harmful to the environment. Specific data with its eco-toxicity details are not yet known.
Tungsten's properties make it best suited for various uses in industries today. However, we still do not know if it is really low in toxicity. Recent studies say that tungsten may not be as harmless as we have believed it to be. Thus, it is advisable to wear protective equipment while handling this metal or its compounds.