aluminum (Al)

A lightweight, silvery-white, ductile,
malleable, metallic element in group IIIA
of the periodic table. It is the
most abundant element in the Earth's crust (8%), but found only in combination,
chiefly in bauxite but also as cryolite,
feldspar, clay,
and many other minerals. It is smelted by the Hall-Héroult process
(see below). Aluminum (British: "aluminium") is widely used for aircraft
parts, engines, window frames, pans, drinks cans, kegs, cooking foil, etc.,
and to form many hard, light, corrosion-resistant
alloys. Its name comes from alumen,
the Latin name for the mineral alum.

Aluminum is extremely useful for several reasons. First, it is light –
weighing only about a third as much as other common metals for the same
volume. It is also strong, and to give the same rigidity need weigh only
half as much as steel. Its strength can be
greatly increased by alloying with other metals.

Second, although aluminum combines readily with other elements, including
oxygen, it does not rust or corrode in the
air, because a thin film of oxide is formed on the surface, and this protects
the metal below. So aluminum has excellent corrosion resistance.

Third, aluminum conducts heat and electricity extremely well. An aluminum
wire will conduct only 60 percent as much electricity as a copper
wire of the same size, but more than twice as much as a copper wire of the
same weight. Its good heat conducting qualities and its resistance to corrosion
have ed to its widespread use in cooking vessels.

atomic number

13

relative atomic mass

26.98154

electron configuration

1s22s22p63s23p1

atomic radius

143.1 pm

oxidation state

3

melting point

660.3°C (1,220.6°F)

boiling point

2,519°C (4,566°F)

relative density

2.69

Discovery and extraction

Compounds of aluminum have been known for centuries, but the metal was first
made from these by Humphry Davy. The metallic
aluminum he produced was too impure for him to have any real idea of its
properties, and a purer metal was first made by the Danish chemist Hans
Oersted in Copenhagen in 1825 and the German
chemist Friedrich Wöhler in 1827. It
was not until 1845 that Wöhler succeeded in producing a sufficient
quantity to discover that it was a very light metal which was malleable.

In later years ways were discovered of making larger quantities of aluminum
through electrolysis – that is,
by passing an electric current through a fused or liquefied aluminum compound.
But the metal remained very expensive, and it was only in 1886 that the
French chemist Hèroult and the American C. M. Hall discovered at
about the same time the method of making aluminum on a larger scale, now
known as the Hall process, which is
still used. This is by electrolysis of alumina
(aluminum oxide) dissolved in a bath of fused cryolite (sodium aluminum
fluoride).

Duralim

One of the most important alloys of aluminum is Duralim, an alloy containing
about 4 percent copper with smaller quantities of magnesium
(1%), manganese (0.7%), and silicon
(0.5%). It was invented in 1908 by a German engineer, Alfred Wilm. This
alloy has been very important in the development of aviation, beginning
with its use for Zeppelins in World War I, owing to its combination of strength
and lightness. It is not as resistant to corrosion as pure aluminum, but
when high corrosion resistance is needed it can be coated nb both sides
with a layer of pure aluminum.

Compounds of aluminum

Compounds of aluminum are trivalent and mainly cationic, though with strong
bases aluminates are formed (see also alum).
Alumina oxide (Al2O3), or alumina,
is a colorless or white solid occurring in several crystalline forms, and
is found naturally as corundum, emery,
and bauxite. Solubility in acid and alkali increases with hydration. Melting
point 2,045°C, boiling point 2,980°C.

Aluminum
chloride (AlCl3) is a colorless crystalline solid, used
as a catalyst (see Friedel-Crafts
reaction). The hexahydrate is used in deodorants and as an astringent.