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particularly in the vicinity of the surface. Specific changes may occur in surface area
and roughness, adsorption of species, lattice defects, formation of passive films, accu-
mulation of dissolution products, precipitation of a solid layer loosely attached to the
surface, and exhaustion of reactants. Mechanistically, these changes may lead to alter-
ation in the equilibrium potentials of the redox couples, the type of reactions involved,
the rate-controlling process, and so on. As a result, OCP may vary drastically depend-
ing on the nature and extent of these changes. The potential may not reach a constant
value if the surface and solution change continuously.
Figure 2.41 illustrates that OCP of a
p
-Si varies with time in three different solu-
tions.
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The different values of OCP in the three solutions are interpreted by Bertagna
et al
.
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as due to the effect of
and
on the exchange current density of the anodic
