■ CONCLUSIONS AND PEDAGOGIC IMPLICATIONS
Simple experiments including those using iron treated with
concentrated sulfuric acid as anode were revisited. The anodic
polarization curve for iron has been measured and it is found
that the curve pattern repeats itself successively when the
potential scan is repeated. This periodic phenomenon has not
been previously emphasized in the literature though terms such
as “dynamic passive film” are commonplace. Logical explanations
for this repeating curve pattern are provided here based
on simple well-known principles such as (i) the charged particle
must move if an electric field is present; (ii) the current is equal
everywhere in a series circuit; (iii) there is no charged area in
metal or solution whether there is current or not; and (iv) the
electric-field shielding principle. Taking into account facts such
as that passive property is common in metals and that the shape
of the anodic polarization curve is dependent upon ion
concentration and metal, all these observations are consistent
with our explanation. The known complex facts, such as the
sustained periodic current oscillations in passivation region
from EAC to Ep in Figure 1A, are explained simply as a special
case of the anodic polarization curve and are detailed in
Supporting Information.
This work apart from its intrinsic importance offers
important lessons to students and others. First, that even
when an experiment has been carried out many times with
consistent results, it can be worthwhile to revisit the work.
Occasionally, as in the present case, new results can be
obtained, but even if not, much can be gained by repeating the
work because the thought processes of the original experimenter
can be followed. Thus, this process of replication can
represent a beneficial learning strategy and can deepen
understanding even if important new revisions are not
established. Further comments of the pedagogic implications
of this work, based on our experience11−16 are given in the
Supporting Information.