We all know that today, elements like silver, gold and platinum are considered precious and significant, both in terms of its value and price. However, there is an astonishing fact that an element, today named as ‘Aluminium’ was once called the ‘Metal of Kings’. This was because pure Aluminium was more expensive to produce than gold until the Hall–Heroult process was discovered. From Alum–to–Aluminum–to–Aluminium, it is a chemical element in the Boron Group having an atomic number 13 and symbol Al. A silvery white, soft and ductile metal, it is the third most abundant element in the Universe and is the most abundant metal in the earth’s crust. About 8% of the earth’s solid surface is made up by Aluminium. Despite its prevalence in the environment, it is not found free in nature and no known life form uses Aluminium salts metabolically. Aluminium is derived from the Latin word ‘alum’ but later in 1807, Sir Humphry Davy proposed the name ‘aluminum’. The element is somewhat decorative, machined, easily formed and casted.
Before its discovery, Aluminium was used by the ancient Greeks and Romans in medicines as an astringent and in dyeing processes. Also, about 85% of Aluminium was used in the tomb of Chou–Chou, a Chinese military leader in the 3rd century. However, it was a mystery about how was it produced. By the end of the 1700s, Humphry Davy extracted sodium and potassium from its oxides by using an electric current, but could not release Aluminium in the similar way. Aluminium was first discovered and isolated by Hans Christian Oersted in Denmark in 1825. He did it by heating Aluminium Chloride with potassium. Yet, what he discovered was an impure sample. The method was systematised by a German chemist Friedrich Wohler in 1827 and accordingly, pure Aluminium was isolated by using sodium instead of potassium.
Though Aluminium is the most abundant metal in the earth’s crust, it is never found free in nature. It is generally found in common minerals like granite and cryolite. Alumina, its oxide, naturally occurs as ruby, sapphire, corundum and emery. Most of the Aluminium today, is obtained from an artificial mixture of Sodium, Aluminium and Calcium fluorides. Generally, Aluminium is obtained from Bauxite ore.
The significant characteristics of Aluminium are:
- Being the second most malleable metal and the sixth most ductile element, Aluminium is light, non–magnetic and non–sparking.
- Aluminium oxide, sulphate and a soluble sulphate with Potassium are Aluminium’s most important compounds.
- Approximately, 92% of the fresh film of Aluminium serves as a good reflector of visible light and approximately 98% as an excellent reflector of medium and far infrared radiation.
- Alloys of Aluminium have a yield strength ranging from 200 MPa–600 MPa whereas the yield strength of pure Aluminium is about 7–11 MPa.
- The element has about one–third of the density and stiffness of steel.
With isotopes ranging from 21 to 42, Aluminium has only one stable isotope, 27Al. This isotope is about 99.9% naturally abundant. Apparently, it has a radioisotope 26Al, that occurs naturally. This isotope is mainly produced from argon by spallation in the atmosphere, which is caused by cosmic–ray protons. The isotopes of Aluminium have been found in the practical application to date marine sediments, manganese nodules, glacial ice, quartz in rock exposures and meteorites.
Common and important uses of Aluminium include:
- The alloys that the element forms with copper, manganese and silicon are very important in the construction of all forms of transport, especially aeroplanes.
- Due to its light weight, it is widely used for window frames, aircraft parts, engines, kegs, drinks cans, etc.
- It is widely used in households as a tin–foil or an aluminium foil.
- With an electrical conductivity of about 60%, it is twice a good conductor of heat and electricity and hence, is used in transmission lines.
- When the element forms a highly reflective coating for both light and heat, evaporated in a vacuum, it does not deteriorate as a silver coating.
- Its coatings are useful in telescope mirrors, decorative paper, packages and toys and so on.
Oral exposure to Aluminium is not harmful but breathing large amounts of it may lead to lung problems such as coughing or changes that show up in the chest X–rays. People suffering from kidney disease store a lot of Aluminium in their bodies. The disease, however, causes less Aluminium to be removed from the body in the form of urine and is mistakenly understood as the reason for bone or brain diseases by the doctors.
