The third most abundant element in the earth's crust (after oxygen and silicon) but with no known biological function. Present in small amounts in many foods but only a small proportion is absorbed. Aluminium salts are found in the abnormal nerve tangles in the brain in Alzheimer's disease, and it has been suggested that aluminium poisoning may be a factor in the development of the disease, although there is little evidence.

Aluminium is used in cooking vessels (the first aluminium saucepan was produced in Cleveland Ohio by Henry Avery in 1890) and as foil for wrapping food, as well as in cans and tubes. Aluminium cans were first used for food and beverages in 1960; tab-opening aluminium cans for beverages first introduced 1962. It is a soft flexible metal, resistant to oxidation and deterioration, although it is dissolved by alkalis. The 'silver' beads used to decorate confectionery are coated with either silver foil or an alloy of aluminium and copper.

Baking powders containing sodium aluminium sulphate as the acid agent were used at one time (alum baking powders), and aluminium hydroxide and silicates are commonly used in antacid medications.

History :

Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. In 1761 Guyton de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first named alumium and later aluminum

Friedrich Wöhler is generally credited with isolating aluminium (Latin alumen, alum) in 1827 by mixing anhydrous aluminium chloride with potassium. The metal, however, had indeed been produced for the first time two years earlier 'but in an impure form' by the Danish physicist and chemist Hans Christian Ørsted. Therefore, Ørsted can also be listed as the discoverer of the metal.

Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it.The Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846 and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium.

Aluminium was selected as the material to be used for the apex of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the project; aluminium was about the same value as silver.

The American Charles Martin Hall of Oberlin, Ohio applied for a patent (U.S. Patent 400,664 ) in 1886 for an electrolytic process to extract aluminium using the same technique that was independently being developed by the Frenchman Paul Héroult in Europe. The invention of the Hall-Héroult process in 1886 made extracting aluminium from minerals cheaper, and is now the principal method in common use throughout the world.

The Hall-Heroult process cannot produce Super Purity Aluminium directly. Upon approval of his patent in 1889, Hall, with the financial backing of Alfred E. Hunt of Pittsburgh, PA, started the Pittsburgh Reduction Company, renamed to Aluminum Company of America in 1907, later shortened to Alcoa. Germany became the world leader in aluminium production soon after Adolf Hitler's rise to power.

By 1942, however, new hydroelectric power projects such as the Grand Coulee Dam gave the United States something Nazi Germany could not compete with, provided them with sufficient generating capacity to produce enough aluminium to manufacture sixty thousand warplanes in four years.

Whether measured in terms of quantity or value, the global use of aluminium exceeds that of any other metal except iron, and it is important in virtually all segments of the world economy.

Relatively pure aluminium is encountered only when corrosion resistance and/or workability is more important than strength or hardness. Pure aluminium serves as an excellent reflector (approximately 99%) of visible light and a good reflector (approximately 95%) of infrared. A thin layer of aluminium can be deposited onto a flat surface by chemical vapour deposition or chemical means to form optical coatings and mirrors.

Pure aluminium has a low tensile strength, but when combined with thermo-mechanical processing, aluminium alloys display a marked improvement in mechanical properties, especially when tempered. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio.

Aluminium readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to loosely as "aluminium," are actually alloys. For example, the common aluminium foils are alloys of 92% to 99% aluminium.

Uses of aluminium :

• Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.)


• Packaging (cans, foil, etc.)


• Water treatment


• Treatment against fish parasites such as Gyrodactylus salaris.


• Construction (windows, doors, siding, building wire, etc.)


• Cooking utensils.


• Electrical transmission lines for power distribution


• MKM steel and Alnico magnets


• Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.


• Heat sinks for electronic appliances such as transistors and CPUs.


• Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.


• In the blades of prop swords and knives used in stage combat.

Aluminium alloys in structural applications :

Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO).

Aluminium is used extensively in many places due to its high strength to weight ratio. However, a designer used to working with steel will find aluminium less well-behaved in terms of flexibility. The problems may often be addressed by redesigning parts dimensionally specifically to address issues of stiffness. For instance by increasing the second moment of area for a pipe or I-beam, an aluminium design can be made both stiffer and lighter than a traditional design.

The strength and durability of aluminium alloys varies widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes. A lack of knowledge of these aspects has from time to time led to improperly designed structures and gained aluminium a bad reputation.

One important structural limitation of aluminium alloys is their fatigue strength. Unlike steels, aluminium alloys have no well defined fatigue limit, meaning that fatigue failure will eventually occur under even very small cyclic loadings. This implies that engineers must assess these loads and design for a fixed life rather than an infinite life.

Another important property of aluminium alloys is their sensitivity to heat. Workshop procedures involving heating are complicated by the fact that aluminium, unlike steel, will melt without first glowing red. Forming operations where a blow torch is used therefore requires some expertise, since no visual signs reveal how close the material is to melting.

Aluminium alloys, like all structural alloys, also are subject to internal stresses following heating operations such as welding and casting. The problem with aluminium alloys in this regard is their low melting point, which make them more susceptible to distortions from thermally induced stress relief. Controlled stress relief can be done during manufacturing by heat-treating the parts in an oven, followed by gradual cooling; in effect annealing the stresses.

The low melting point of aluminium alloys has not precluded their use in rocketry; even for use in constructing combustion chambers where gases can reach 3500 K. The Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat region; in fact the extremely high thermal conductivity of aluminium prevented the throat from reaching the melting point even under massive heat flux, resulting in a reliable and lightweight component.

Household wiring :

Aluminium has about 65% of the conductivity of copper, the traditional household wiring material. In the 1960s aluminium was considerably cheaper than copper, and so was introduced for household electrical wiring in the United States, even though many fixtures had not been designed to accept aluminium wire.

However, in some cases the greater coefficient of thermal expansion of aluminium causes the wire to expand and contract relative to the dissimilar metal screw connection, eventually loosening the connection.

Also, pure aluminium has a tendency to "creep" under steady sustained pressure (to a greater degree as the temperature rises), again loosening the connection. Finally, Galvanic corrosion from the dissimilar metals increased the electrical resistance of the connection.

All of this resulted in overheated and loose connections, and this in turn resulted in some fires. Builders then became wary of using the wire, and many jurisdictions outlawed its use in very small sizes, in new construction. Eventually, newer fixtures were introduced with connections designed to avoid loosening and overheating.

At first they were marked "Al/Cu", but they now bear a "CO/ALR" coding. In older assemblies, workers forestall the heating problem using a properly-done crimp of the aluminium wire to a short "pigtail" of copper wire. Today, new alloys, designs, and methods are used for aluminium wiring in combination with aluminium terminations.

Source: Wikipedia