Aluminium

Aluminium, Al, is a metallic element found in Group IIIb of the periodic table. Aluminium is the most abundant metal in the world (approximately 8.1% by weight)

Atomic Number : 13
Atomic Mass : 26.97 (approximately)
Melting Point : 660 degC
Boiling Point : 2467 degC
Density : 2.7.

Discovery

Aluminium in the form of its oxide was shown as being different from Lime, Ca(OH)2, by A S Marggraf in 1754AD. Aluminium was isolated, as a gray metallic powder, by F Wohler in 1827AD, after he heated Anhydrous Aluminium Chloride, AlCl3, with Potassium metal.

Occurrence

Aluminium is highly reactive and does not occur in the free state. However, it is widely distributed and it is third in abundance on earth after Oxygen and Silicon.
Aluminium exists primarily as Alumino-Silicates (i.e. as Felspar, NaAlSi3O8, or KAlSi3O8, or CaAl2Si2O8), in igneous rocks and as Clays, H4Al2Si2O9, in sedimentary rocks.
Aluminium has three principal ores

Gibbsite or Hydrargillite, Al2O3.3H2O,
Bauxite, Al2O3.2H2O, Diaspore, Al2O3.H2O, and
Cryolite, AlF3.3HF.

Aluminium also occurs in the form of its Aluminium Oxide, Al2O3, in the semiprecious stones. The colouration in these gems is caused by trace quantities of impurities :

Emerald, Sapphire (coloured blue by Cobalt Oxide, CoO), and
Ruby (coloured blue by Chromium Oxide, Cr2O3).

Manufacture

Aluminium is manufactured by the electrolysis of fused mixture of Bauxite, Al2O3.2H2O, and Cryolite, AlF3.3HF.

Properties

Aluminium is a bluish-white metal, which can be highly polished. However, it is usually seen as a dull metal, due to a thin layer of Aluminium Oxide, Al2O3, on its surface, which protects against further oxidation.
Aluminium is ductile and malleable and can be drawn into wire and rolled into sheets.
Aluminium is a good conductor of heat and electricity.

Uses

The typical metallic properties of aluminium cause it to be used

in electrical conductors, where it lightness is useful for overhead wires,
for cooking utensils,
in the form of its salts as mordants in dyeing,
in the welding agent, Thermite,
is used in alloys, where small quantities of other metals significantly increase its strength and mechanical properties.
in the form of its oxide, Alumina, Al2O3, in the synthetic ruby used in laser tubes.

Reactions

Aluminium reacts rapidly with the Oxygen in air to form Aluminium Oxide, Al2O3, which forms a tough layer on the surface of the metal, thereby preventing any further reaction. This aluminium oxide layer can be thickened by a process known as anodising, which involves using the aluminium object as the anode in an electrolytic cell.

Detection and Analysis

Aluminium is usually identified by the gelatinous precipitate of its hydroxide which forms when alkali is added to a solution of its salts.

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