Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Example 6- K:

Aluminium oxide as protection against corrosion

With a standard reduction potential of -1.7 volt aluminium ought to corrode relatively easy by being

exposed to water and oxygen. Nevertheless a thin layer of aluminium oxide Al 2 O 3 is formed by contact

with oxygen as sketched on the figure below:

Figure 6- 10: Protecting oxide layer

Formation of aluminium oxide on aluminium metal.

Whereas the oxidation of aluminium metal has a standard reduction potential of -1.7 volt the oxidation of

Al 2 O 3 has only a standard reduction potential of -0.6 volt making aluminium oxide almost as corrosion

resistant as the noble metal gold.

Iron forms also an oxide layer (better known as rust) on the surface but on the contrary to aluminium oxide

the layer does not have the same adhesion and thereby peels off. Hereby new iron metal may be exposed to

oxygen and water whereby the corrosion process may continue. This is the subject for the following example:

Electrochemistry