Corrosion protection
Corrosion protection can be effected by the corrosion itself and by cathodic protection.
Protection by corrosion
Corrosion protection may be activated by corrosion itself, when uniform layers of reaction products form a protective layer on the surfaces. Corrosion protection can also be achieved by keeping the metallic material separated from the corrosive medium by applying protective layers or by electrochemical means such as cathodic protection.
Cathodic protection
Cathodic protection is an electrochemical process in which the metal surface is polarised to a non-precious potential, so that the reduction reactions can then take place on the resulting layer. The corrosion rate is relatively low as a result and local corrosion phenomena are prevented.
Methods of cathodic protection
- The metal to be protected is electrically connected with a second, less noble metal and both are immersed in the corrosive medium. A corrosive cell is formed, in which the less noble metal dissolves anodically (protection anode) and has to be renewed at intervals, whereas the more noble part is protected cathodically.
- The metal to be protected is connected to the negative pole of a direct current voltage source and forms an electric circuit with an inert anode and the medium.
