Aluminium
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English
Pronunciation
Noun
aluminium, symbol Al
- A light, silvery metal made from bauxite, and a chemical element (symbol Al) with an atomic number of 13. Spelled aluminum in the United States. (Read more at Wikipedia)
Aluminium is a soft and lightweight but strong metal with a dull silver-gray appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air and which prevents further corrosion. Aluminium is about one-third as dense as steel or copper; is malleable, ductile, and easily machined and cast; and has excellent corrosion resistance and durability. It is also nonmagnetic and nonsparking and is the second most malleable metal (behind gold) and the sixth most ductile.
Applications
Whether measured in terms of quantity or value, the use of aluminium exceeds that of any other metal except iron, and it is important in virtually all segments of the world economy. Pure aluminium is soft and weak, but it can form alloys with small amounts of copper, magnesium, manganese, silicon, and other elements to make alloys having a variety of useful properties.
These alloys form vital components of aircraft and rockets. When aluminium is evaporated in a vacuum it forms a coating that reflects both visible light and radiant heat. These coatings form a thin layer of protective aluminium oxide that does not deteriorate as silver coatings do. Coating telescope mirrors is another use of this metal.
Some of the many uses for aluminium are in
- Transportation (automobiles, airplanes, trucks, railcars, marine vessels, etc.)
- Packaging (cans, foil, etc.)
- Water treatment
- Construction (windows, doors, siding, etc.; however it has fallen out of favor for end-user wiring[1])
- Consumer durable goods (appliances, cooking utensils, etc.)
- Electrical transmission lines (although its electrical conductivity is only 60% that of copper, it's lighter in weight and lower in price[2])
- Machinery.
- Despite its usual magnetically resistant nature, it is used in MKM steel and Alnico magnets.
- Super Purity Aluminium (SPA, 99.980%-99.999% Al) is used in electronics and CDs.
Its oxide, alumina, is found naturally as corundum, emery, ruby, and sapphire and is used in glass making. Synthetic ruby and sapphire are used in lasers for the production of coherent light.
Aluminium oxidizes very energetically and as a result has found use in solid rocket fuels and thermite.
History
The oldest suspected (although unprovable) reference to aluminium is in Pliny the Elder's Naturalis Historia:
One day a goldsmith in Rome was allowed to show the Emperor Tiberius a dinner plate of a new metal. The plate was very light, and almost as bright as silver. The goldsmith told the Emperor that he had made the metal from plain clay. He also assured the Emperor that only he, himself, and the Gods knew how to produce this metal from clay. The Emperor became very interested, and as a financial expert he was also a little concerned. The Emperor felt immediately, however, that all his treasures of gold and silver would fall in value if people started to produce this bright metal of clay. Therefore, instead of giving the goldsmith the regard expected, he ordered him to be beheaded.
Ancient Greeks and Romans used salts of this metal as dyeing mordants and as astringents to bind wounds, and alum is still used as a styptic. In 1761 Guyton de Morveau proposed calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he named (see Spelling below for more information on the name).
Friedrich Wöhler is generally credited with isolating aluminium (Latin alumen, alum) in 1827. However, this metal was produced for the first time in impure form two years earlier by Danish physicist and chemist Hans Christian Ørsted.
Charles Martin Hall received the patent(400655) in 1886, on electrolytic process to extract aluminium. Henri Saint-Claire Deville (France) improved Wöhler's method (1846) and presented these in a book in 1859 with two improvements to the process as to substitute potassium to sodium and double instead of simple chlorure. The invention of the Hall-Héroult process in 1886 made extracting aluminium from minerals inexpensive, and so it is now in common use throughout the world.
Occurrence and resources
Although Al is an abundant element in Earth's crust (8.1%), it is very rare in its free form and was once considered a precious metal more valuable than gold (It is said that Napoleon III of France had a set of aluminium plates reserved for his finest guests. Others had to make do with gold ones). It is therefore comparatively new as an industrial metal and has been produced in commercial quantities for just over 100 years.
Aluminium was, when it was first discovered, extremely difficult to separate from the rocks it was part of. Since the whole of Earth's aluminium was bound up in the form of compounds, it was the most difficult metal on earth to get, despite the fact that it is one of the planet's most common.
Recovery of this metal from scrap (via recycling) has become an important component of the aluminium industry. Recycling involves simply melting the metal, which is far less expensive than creating it from ore. Refining aluminium requires enormous amounts of electricity; recycling it requires only 5% of the energy to produce it. A common practice since the early 1900s, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960s when the exploding popularity of aluminium beverage cans finally placed recycling into the public consciousness. Sources for recycled aluminium include automobiles, windows and doors, appliances, containers and other products.
Aluminium is a reactive metal and cannot be extracted from its ore, bauxite (Al2O3), through reduction with carbon. Instead it is extracted by electrolysis – the metal is oxidized in solution and then reduced again to the pure metal. The ore must be in a liquid state for this to occur. However, bauxite has a melting point of 2000°C, which is too high a temperature to achieve economically. Instead, the bauxite for many years was dissolved in molten cryolite, which lowers the melting point to about 900°C. But now, cryolite has been replaced by an artificial mixture of aluminium, sodium, and calcium fluorides. This process still requires a great deal of energy, and aluminium plants usually have their own power stations nearby.
The electrodes used in the electrolysis of bauxite are both carbon. Once the ore is in the molten state, its ions are free to move around. The reaction at the negative cathode is
- Al3+ + 3e- → Al
Here the aluminium ion is being reduced (electrons are added). The aluminium metal then sinks to the bottom and is tapped off.
The positive anode oxidizes the oxygen of bauxite, to form oxygen gas:
- 2O2- → O2 + 2e-
This cathode must be replaced often because the oxygen gas formed is extremely hot, and eats away the carbon electrode in the following reaction:
- O2 + C → CO2
Despite the cost of electrolysis, aluminium is a very widely used metal. Aluminium can now be extracted from clay, but this process is not economical.
Electric power represents about a third of the cost of refining aluminium. For this reason, refineries tend to be located where electric power is plentiful and inexpensive, such as the United States Pacific Northwest, the South Island of New Zealand, and Quebec in Canada.
China is currently (2004) the top world producer of aluminium.
Isotopes
Aluminium has nine isotopes, whose mass numbers range from 23 to 30. Only Al-27 (stable isotope) and Al-26 (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally. Al-26 is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of Al-26 to beryllium-10 has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales.
Translations
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External links
For etymology and more information refer to: http://elements.vanderkrogt.net/elem/al.html (A lot of the translations were taken from that site with permission from the author)
