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Aluminium - Resistance to Corrosion.
Corrosion is the name given to the process
where a metal reacts with oxygen in
the air to form a metal oxide.
Corrosion is the reverse of the process used to extract the metal.
If the metal is iron, corrosion is
called rusting.
In general, the more reactive a
metal is the more quickly it will corrode.
Aluminium
is a reactive
metal.
It is above carbon in the reactivity series but is resistant to corrosion
because aluminium reacts with oxygen in
the air
and forms a thin layer of aluminium oxide
(Al2O3).
The oxide layer covers the surface of
the aluminium metal
and prevents any further reaction (corrosion) from happening.
The thickness of the oxide layer can be increased by anodising.
The oxide
layer will react with an
acid or
alkali
to form an aluminium salt
+ water.
The exposed aluminium metal will then itself react
with acid or
alkali to form the aluminium salt
+ hydrogen.
It is therefore best to avoid contact of aluminium cookware
with citrus
fruits or vinegar (acids),
or alkali cleaners such as caustic
soda (sodium
hydroxide).
Aluminium in food is
a health hazard
and has been associated with
Alzheimer's disease.
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