Measured Potentials as Related to Corrosion And Polarization in Local Cells

Following a brief review of the theory of reversible electrode potentials, irreversible electrode potentials of corroding metals are discussed with particular reference to corrosion rates. Experiments in sea water provide evidence that neither reversible nor irreversible potentials can be used to estimate corrosion rates. The Mears and Brown concept of local cell action explains this lack of co-ordination. Polarization properties similarly account for the observed galvanic corrosion when dissimilar metals and alloys are coupled. Anodic and cathodic currents from an external source were applied in separate experiments to steel in flowing sea water. Potentials measured at several current densities permitted the construction of anodic and cathodic polarization curves. These potentials and corresponding corrosion rates permitted the construction of approximate polarization curves for the local anodes and cathodes on steel in flowing sea water.