History, Analysis and Uses of Aluminium
How Aluminium was discovered
The art of pottery making was developed in northern Iraq about 5300 B.C. The clay used for making the best pottery consisted largely of a hydrated silicate of aluminium. Certain other aluminium compounds such as alums were widely used by the Egyptians and Babylonians as early as 2000 B.C. In vegetable dyes, various chemical processes and for medicinal purposes. It was generally known as the metal of clay and for thousands of years could not be separated by any known method from its link with other elements. As relatively late as 1782 the French chemist, Lavoisier, said it was the oxide of an unknown metal.
Aluminium, as we understand it, was isolated early in the 19th century. Lavoisier's opinion was repeated by Sir Humphrey Davy in 1808. He gave it the more scientific sounding name aluminum ( pronnounced aloominum) His spelling is still used in North America but elsewhere in the world the spelling aluminium, following the suggestion of Henri Sainte-Clair Deville, is used. In 1809 Davy fused iron in contact with alumina in an electric arc to produce an iron aluminium alloy; for a split instant, before it joined the iron, aluminium existed in its free metallic state for perhaps the first time since the world was formed. In 1825 H.C. Oerstedt, a Dane, produced a tiny sample of aluminium in the laboratory by chemical means.
Twenty years later the German scientist, Frederick Wohler, produced aluminium lumps as big as pinheads. In 1854 Sainte-Clair Deville had made improvements in Wohler's method and produced aluminium globules the size of marbles. He was encouraged by Napoleon lll to produce aluminium commercially and at the Paris exhibition in 1855 aluminium bars were exhibited next to the crown jewels. It was not until 31 years later, however, that an economical way of commercial production was discovered.
On February 23, 1886, a 22-year-old American, Charles Martin Hall, worked out the basic electrolytic process still in use today. Hall had begun his experiments while still a student at Oberlin College, Ohio. He achieved his success, after graduation, with home-made apparatus in the family wood shed. He separated aluminium from the oxygen with which it is chemically combined in nature by passing an electric current through a solution of cryolite and alumina.
Almost simultaneously, Paul L.T. Heroult arrived at the same process in France. However, he did not at first recognise its importance. He worked along another line in the development of aluminium alloys. In 1888 the German chemist, Karl Joseph Bayer, was issued a German patent for an improved process for making Bayer aluminium oxide (alumina). The foundation of the aluminium age was complete. The Bayer & Hall-Heroult processes freed our planet's most plentiful and versatile structural element for widespread use.
Aluminium is a metallic element that comes from the ore bauxite. Aluminium is one of about 100 basic elements out of which the physical universe is built. In other words, it was created billions of years ago when the whirling clouds of hydrogen under constant pressure with electro-magnetic forces collided to form new elements. When Earth's mass cooled, aluminium mixed with water and oxygen to form the original material from which bauxite is made. It is called bauxite after Les Baux, France, where it was discovered in 1821.
Converted to aluminium by modern processes, it becomes a light metal which can be given great strength by alloying with other metals. It is inherently corrosion-resistant, conducts heat and electricity yet can be processed to reflect light and radiant energy. Aluminium is classified non-toxic. It is non-magnetic. It can be formed by all known metal working processes. Its intrinsic properties make it able to be used in in many circumstances where other materials would not be considered.
How Aluminium is made
The bauxite is mined by various processes. Once mined it is finely crushed for refining and recovery of alumina, the base from which aluminium is made. The separation of the alumina from bauxite is a complicated process. This involves the use of a caustic soda solution heated under pressure to dissolve the alumina. Impurities are filtered out of the solution in the form of a mud-like material. The filtered solution is cooled and alumina is recovered by precipitation in a hydrate form. The resulting fine crystals are then heated in long revolving kilns to drive off the water of crystallisation.
The product is alumina in a white powder form. Aluminium metal is produced in large steel shells lined with carbon. These shells are known in the industry as pots and are arranged in long rows called pot lines. Alumina is mixed with cryolite in the pots and large quantities of electricity are introduced to reduce the alumina into aluminium and oxygen. The process is continuous and molten metal is siphoned from the pots at regular intervals.
How Aluminium is turned into products
Once aluminium is produced it can be made into forms ready for manufacturers to convert into finished products. Industries requiring aluminium may specify from a range of alloys and their metal can be supplied in the form of ingots, extruded shapes, rod, tube, bar, sheet, plate and foil.
One of the best known forms of aluminum is sheet, which has many applications.The process starts with special alloy rolling ingots. These are pre-heated to rolling temperatures, then are fed into a hot mill with the ingot passed back and forth through the mill. The process results in plate, with thinner sheets being formed by further passes between rolls under extreme pressure.it becomes longer and thinner in the direction in which the plate or sheet is moving.
Perhaps the most remarkable of all these forms is foil, which is aluminium metal that has been rolled very thin so that it is pliable yet strong. Aluminium foil is widely used in kitchens and food packaging.
Aluminium extrusions have been used commercially for many years. The process involves a heated billet being pushed under tremendous pressure through a die, the metal taking the shape of the holes in the die. Extrusions are mostly used to reduce the weight or number of parts in an assembly, or to achieve shapes that cannot be produced satisfactorily any other way.
The uses of Aluminium
The characteristics of aluminium combine to make aluminium a most versatile material for a host of applications.
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