Chemistry Reference
In-Depth Information
In the case where the anodic dissolution is inhibited, e.g., by surface adsorption
of a chemical species, the anodic curve becomes This will result in a more positive
corrosion potential (from to if the cathodic reaction remains unchanged.
In such a situation the corrosion current is reduced with a more positive potential rela-
tive to the original value. On the other hand, if the anodic dissolution kinetics remains
unchanged but the rate of the cathodic reactions is changed from curve
to curve
the potential also becomes more positive (from
to
However, in this case the
corrosion current is increased with a more positive potential.
The anodic curve becomes in Fig. 1.26 when the surface is passivated. If the
cathodic reaction is unchanged, the corrosion potential of the electrode becomes
which is more positive than
The corrosion current is generally much smaller than
that at
The corrosion potential values that are much more positive than are usually
associated with both the passivation of the electrode surface and the presence of
oxidizing agents in the solution. The cathodic and anodic polarization curves in such a
solution are illustrated by and the coupling of which yields the corrosion poten-
tial The dissolution rate in this situation is usually very low. However, if the
surface is not passivated, the dissolution rate can be very high in the presence of oxi-
dizing agents, which is the case for etching of semiconductors in solutions containing
oxidizing agents. This can be appreciated by coupling curves and in Fig. 1.26.
A decrease in potential can be caused by either faster anodic dissolution kinetics
or a slower cathodic reaction. For example, a decrease in corrosion potential due to
deaeration of a solution is usually observed. Deaeration removes the dissolved oxygen
and thus reduces the cathodic reaction rate.
