DISTRIBUTION OF POTENTIAL AROUND A SCRATCH IN A PASSIVE FILM

A Fourier analysis technique has been used to solve the problem of the potential distribution around a long narrow scratch in a passive film on an electrode surface. Analytic solutions have been obtained for situations where linear polarization kinetics may be assumed for the unscratched region, and where the current density is constant over the scratch and very much greater than the current density over unscratched regions. If the half-width l of the scratch is very much smaller than the Wagner polarization parameter for the unscratched region Lc, a simple expression is obtained for the potential distribution close to the scratch. There is a small additional increase in electrode potential at the scratch, but the main increase in potential is over a distance characterized by Lc and not by the size of the scratch. The potential within the electrolyte and along the electrode depends mainly on the logarithm of distance from the center of the crack. There is an angular dependence of the potential only for distances < ~ 2l from the center of the scratch. © 1979, The Electrochemical Society, Inc. All rights reserved.