Journal of Dental Research, Vol 76, 1869-1878, Copyright © 1997 by International & American Associations for Dental Research Online Journals
Connections between polarization curves and log(a[i]/a[ref])-pe diagram
S. Olsson, M. Bergman, M. Marek and A. Berglund
Department of Dental Materials Science, Faculty of Odontology, University of Umea, Sweden.
When reading papers concerning studies of corrosion of dental amalgam and
its phases by means of polarization curves, one often finds it difficult to
understand the reasons for the chemical reactions proposed from the form of
the polarization curve. Thermodynamic data represented in the form of
log(a[i]/a[ref])-pe diagrams, i.e., the logarithm of the activity of a
metal or an alloy with reference to the activity of the corresponding metal
ion, as a function of pe (a recalculated form of the potential), make it
possible for one to determine which chemical reactions can occur on the
specimen surface or in the solution within the potential difference used in
the polarization experiment and to decide which of these reactions is the
most probable. The hypothesis examined in this study is that a
log(a[i]/a[ref])-pe diagram can be used in the interpretation of
polarization curves. Potentiodynamic polarization curves and
log(a[i]/a[ref])-pe diagrams were compared for the corrosion of Ag, Hg, and
gamma 1 with and without Sn. It was found that there was a connection
between the polarization curves and the log(a[i]/a[ref])-pe diagrams. From
the composition of the specimens and the solution and by means of
thermodynamic data, pe values for solid corrosion products and relative
concentrations of soluble complexes at these pe values were obtained
independently of the polarization curves. A much more reliable value for
the nobility of metals and alloys was attained by use of the
log(a[i]/a[ref])-pe diagrams than by use of the potential of the starting
point of the polarization curves. It was found that pe corresponding to the
potential of the starting point of the polarization curves in de-aerated
synthetic saliva was obtained about two pe units before pe of the most
insoluble solid compound formed on the specimen surface or in the solution.
