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Metals And Alloys

  Metals and alloys (a mixture of two or more metals) play a fundamental part in the structure of the modern world, but the use of metals by man dates back to prebiblical times. The first metals used were those that occurred naturally and appeared on the Earth\'s surface such as gold, silver, iron and copper. These supplies were soon exhausted, and it was not until the Bronze and Iron Ages that it was discovered how to extract metals from their ores, where the metal is chemically combined with other elements such as sulphur and oxygen. As dependency upon metals grew, the techniques to locate and recover the metals from their ores became more sophisticated. Such metals as copper, zinc and lead are extremely rare in the Earth\'s crust, but they have all become an integral factor in today\'s society. The availability of ores depends not only on their scarcity but on how easy it is to extract and exploit the ores.

The use of iron and steel account for around 95% of all metal products in the Western world. The process of reducing iron oxides to metallic iron is smelting. This involves heating the iron ores along with carbon to produce carbon dioxide and iron. This process was carried out using charcoal until Abraham Darby (1677 - 1717) succeeded in smelting iron from coke (which could be easily produced from coal). This raw iron or ‘pig iron’ (so-called from the shape of the lumps produced by the process) can be melted again to remove impurities and have carbon added to it to produce steel which is much stronger and can deform more before breaking. Cast iron is very brittle and snaps with little deformation. Steel may have other metals added to it, in order to produce alloys that have very useful properties. The addition of nickel and chromium is used in the manufacture of stainless steel, while the addition of cobalt, molybdenum, tungsten or vanadium produces hard-wearing steel for cutting tools.

Although iron has been used for over 4,000 years, the most common metal found in the Earth\'s crust, aluminium, was only isolated for the first time in 1825 by the Danish physicist Oersted. Aluminium has many uses such as thin foil sheets for food wrapping, the structure of aircraft and in the electrical supply industry as transmission lines.

Another metal in common industrial use is copper and its alloys such as brass and bronze. As well as being a good electrical conductor, it is also used in coinage and in plumbing. Other metals such as gold, silver, tin, lead, chromium, mercury, platinum, magnesium and zinc all have their specific applications, but probably the use of uranium in nuclear power stations causes more controversy than the use of any other metal or alloy.

Metals are being used at an alarming rate as the Third World countries try to catch up with the rest of the world, and the supplies of such scarce metals as silver and platinum are in doubt. A substitute material may be found in order to compensate for such scarcity, but this may not always be possible. Another factor to take into consideration is the fact that as technology becomes more sophisticated the extraction of scarce ores may become viable in the future. AA

Further reading W. Alexander and , A. Street, Metals in the Service of Man; , J.E. Gordon, The New Science of Strong Materials.



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