Variation of potential around a pit

Abstract

A technique using integrals of Bessel Functions has been used to solve the problem of the distribution of potential around a corrosion pit. Analytic solutions have been obtained for situations where linear polarization kinetics may be assumed for the unpitted electrode, and where the current density over the pit is much greater than the current density elsewhere. Although the analysis is more complicated than for a scratch the final result is fairly simple, provided that the radius of the pit a is small compared with the Wagner polarization parameter L c . For a « L c the potential is independent of the polarization parameter L c , and the ersults of zeroth order in a/ L c , reduce to those for a disc electrode imbedded in an insulating plane. Expressions for the potential distribution are also given to first order in a/ L c . Unlike the equivalent situation for a scratch, the potential differs from the free corrosion potential for the unpitted electrode only in the immediate vicinity of the pit.