Inhibition, corrosion Tafel line

Kaesche and Hackerman (13) have investigated the inhibition of several aliphatic and aromatic amines on pure iron corroding in IN hydrochloric acid. These authors observed in thirteen out of fourteen cases that the inhibition was both anodic and cathodic, albeit predominantly anodic. The exception was methylamine which acted only cathodically. In the case of the corrosion inhibition on pure iron by B-naphthoquinoline in sodium sulfate/sulfuric acid solution (13). one observes a simple parallel shift of the anodic and cathodic Tafel lines towards smaller values of current density. Here the effect is almost symetrical, indicating that this inhibitor acts to the same extent upon anodic and cathodic reaction rates. Therefore, the effect of B-naphthoquinoline can be explained on the basis that its adsorption blocks a fraction 0 of the metal surface for all electrode reactions. If equation 9 describes the external polarization behavior in terms of a function of the partial current potential relationship for the anodic and cathodic reactions in the usual terms ... 

In many early studies iron dissolution was investigated as part of corrosion and inhibition at open-circuit potential imder an Rj-saturated atmosphere, no accoimt being taken of the interference of the Hj/H reaction with the Tafel slopes [63,64], Even under an inert atmosphere, the anodic parameters may be affected by slow hysteresis phenomena resulting in steeper Tafel lines [65-69],... 

As mentioned above, inhibitors may block anodic metal dissolution or the cathodic reduction reaction or both processes simultaneously. If the cathodic reaction is inhibited, the related Tafel line of Figure 1.45a is shifted to negative potentials. As a consequence, the rest potential Er shifts to a more negative value Er, and the related corrosion current density from z c to the smaller value i i- If the anodic metal dissolution is inhibited, the related... 

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