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.
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.
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
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 :
- Gibbsite or Hydrargillite, Al2O3.3H2O,
- Bauxite, Al2O3.2H2O, Diaspore, Al2O3.H2O, and
- Cryolite, AlF3.3HF.
- Emerald, Sapphire (coloured blue by Cobalt Oxide, CoO), and
- Ruby (coloured blue by Chromium Oxide, Cr2O3).
Aluminium is manufactured by the electrolysis of fused mixture
of Bauxite, Al2O3.2H2O, and Cryolite, AlF3.3HF.
- 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
- Aluminium is ductile and malleable and can be drawn into wire
and rolled into sheets.
- Aluminium is a good conductor of heat and electricity.
The typical metallic properties of aluminium cause it to be used
- in electrical conductors, where it lightness is useful for
- 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.
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
Detection and Analysis
Aluminium is usually identified by the gelatinous precipitate of
its hydroxide which forms when alkali is added to a solution of
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