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.
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
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.
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.
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
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.
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.
Uses of aluminium :
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.
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.
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 :
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.
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.