Oxygen absorption mechanism:

One steel plate is required for the study of this mechanism. This is localized attack, part which is in contact with dust or moisture affects first and results in the formation of cavity, corrosion continues through narrow path & undergoes anodic reaction. Part which is unaffected behaves like cathode as it undergoes reduction reaction. Here cathodic area is large & anodic area is small but corrosion is very serious & is beyond control.

$Fe → Fe^{++} + 2e^- $

$H_2O + \frac{1}{2} O_2 +2e^- → 2OH^- $

$Fe^{++} + OH^- → Fe (OH)_2$

$4 Fe (OH)_2 +2H_2O +O_2→ 4Fe (OH)_3$