Reconsidering differential aeration cells

The differential aeration cells are responsible in practice for multiple corrosion forms. The established tension gradients between the cathodic and anodic areas are quite reduced, and consequently both electrodes stay submitted also to corrosion phenomena due to local-action cells. By analysing the theoretical current-potential curves it is shown that differential aeration cells are not responsible for an increase of the electrode corrosion in the oxygen-starved electrolyte in the absence of secondary effects.Differential aeration cells developed on normal carbon steel were investigated in H₂CO₃/HCO₃⁻/CO₃²⁻ solutions of different pH values. The results from polarization data and immersion corrosion tests of coupling indicated have shown the following: (1) the electrode in the aerated zone, for each one of the chosen pH, tends to attain the same potential of the electrode in the deaerated zone; (2) an alkalization of the electrolyte in the aerated and deaerated zones for initial pH 5 and 7.5 in the system; (3) the current density that cross the macrocell is little, of the same order for all pH, and does not justify the observed corrosion rate in both electrodes; (4) there is a polarity inversion of the electrodes for the pH 5 and 7.5; (4) the observed corrosion rate in each one of the tested solutions was practically the same for the aerated and deaerated electrodes. An explanation for this behaviour is given.