Applied example (corrosion)
Many metals form an oxide coating on reaction with oxygen in the atmosphere.
The metal is the reductant as in:
4Al(s)
4Al3+ + 12e–
Oxygen is the oxidant as in:
O2(g) + 4e– O2–
The overall reaction is:
4Al(s) + 3O2(g) 2Al2O3(s)
If, as for aluminium, the oxide coating adheres strongly to the surface of the metal, the metal is protected from further reaction with the atmosphere. However, in the case of iron, the oxide layer flakes off, forming what we know as rust.
Iron is sometimes protected from corrosion by covering the surface with substances which form oxide layers which are impervious such as tin in so-called tin-cans and zinc in galvanised iron.
The next section of this module shows that the degree to which tin and zinc protect iron is quite different if the surface metal layer is broken.
The metal is the reductant as in:
4Al(s)
4Al3+ + 12e–Oxygen is the oxidant as in:
O2(g) + 4e–
O2–The overall reaction is:
4Al(s) + 3O2(g)
2Al2O3(s)If, as for aluminium, the oxide coating adheres strongly to the surface of the metal, the metal is protected from further reaction with the atmosphere. However, in the case of iron, the oxide layer flakes off, forming what we know as rust.
Iron is sometimes protected from corrosion by covering the surface with substances which form oxide layers which are impervious such as tin in so-called tin-cans and zinc in galvanised iron.
The next section of this module shows that the degree to which tin and zinc protect iron is quite different if the surface metal layer is broken.