to dissolution of other acidic oxides from the atmosphere). This spot behaves as cathode with the reaction Cathode: O (g) + H + (aq) + e – ¾® H O (l) | | H O H O = . V The overall reaction being: 2Fe(s) + O (g) + 4H + (aq) ¾® 2Fe + (aq) + H O (l) (cell) = . V The ferrous ions are further oxidised by atmospheric oxygen to ferric ions which come out as rust in the form of hydrated ferric oxide (Fe O .
x H O) and with further production of hydrogen ions. Prevention of corrosion is of prime importance. It not only saves money but also helps in preventing accidents such as a bridge collapse or failure of a key component due to corrosion. One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere.
This can be done by covering the surface with paint or by some chemicals (e.g. bisphenol). Another simple method is to cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object. An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object.