Aluminium (or aluminum in North American English) is the chemical element in the periodic table with the symbol Al and atomic number 13. A silvery and ductile member of the poor metal group of elements, aluminium is found primarily as the ore bauxite and is remarkable for its resistance to oxidation (aluminium is actually almost always already oxidized, but is usable in this form unlike most metals), its strength, and its light weight. Aluminium is used in many industries to make millions of different products and is very important to the world economy. Structural components made from aluminium are vital to the aerospace industry and very important in other areas of transportation and building in which light weight, durability, and strength are needed.
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.
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
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.
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:
This cathode must be replaced often because the oxygen gas formed is extremely hot, and eats away the carbon electrode in the following reaction:
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.
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.
Cosmogenic Al-26 was first applied in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial Al-26 production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further Al-26 production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that Al-26 was relatively abundant at the time of formation of our planetary system. Possibly, the energy released by the decay of Al-26 was responsible for the remelting and differentiation of some asteroids after their formation 4.6 billion years ago.
Aluminium is one of the few abundant elements that appears to have no beneficial function in living cells, but a few percent of people are allergic to it — they experience contact dermatitis from any form of it: an itchy rash from using styptic or antiperspirant products, digestive disorders and inability to absorb nutrients from eating food cooked in aluminium pans, and vomiting and other symptoms of poisoning from ingesting such products as Kaopectate® (anti-diarrhea product), Amphojel®, and Maalox® (antacids). In other persons, aluminium is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts, although the use of aluminium cookware, popular because of its corrosion resistance and good heat conduction, has not been shown to lead to aluminium toxicity in general. Excessive consumption of antacids containing aluminium compounds and excessive use of aluminium-containing antiperspirants are more likely causes of toxicity. It has been suggested that aluminium may be linked to Alzheimer's disease, although that research has recently been refuted.
Care must be taken to prevent aluminium from coming into contact with certain chemicals that can cause it to rust or decay quickly. For example, just a small amount of mercury applied to the surface of a piece of aluminium can break up the normal aluminium oxide barrier usually present. Within a few hours, even a heavy structural beam can be significantly weakened. For this reason, mercury thermometers are not allowed on many airliners, as aluminium is a common structural component in aircraft.
The official IUPAC spelling of the element is aluminium; however, Americans and Canadians generally spell and pronounce it aluminum. Charles Martin Hall, who patented the electrolytic process, misspelled its name on an advertising flyer; due to the explosive popularity of the metal after he developed a more efficient process, most Americans adopted the new spelling. This change was accepted in America, but questioned in Britain because it did not conform to the -ium suffix precedent set by potassium, sodium, magnesium, calcium, and strontium, other newly discovered elements of the period. Thus, the aluminium spelling became the most common in Britain. The United States continued to use aluminum although the official name used in both the United States and Britain in the field of chemistry remained aluminium. In 1926 the American Chemical Society decided officially to use aluminum in its publications.
In 1990 the IUPAC adopted aluminium as the standard international name for the element. Aluminium is also the name used in French, Dutch, German, Danish, Norwegian, and Swedish; Italian uses alluminio, Portuguese alumínio and Spanish aluminio. (The use of these words in these other languages is one of the reasons IUPAC chose aluminium over aluminum.) In 1993, IUPAC recognized aluminum as an acceptable variant, but still prefers the use of aluminium.