A theoretical analysis of the electrochemical noise during the induction period of pitting corrosion in passive metals: Part 2. The current noise associated with halide nucleus formation in the passive film

Abstract

The formation of halide nuclei in the passive film during the induction period of pitting corrosion in passive metals is discussed using a stochastic model concerning the growth/diminishing processes of the hemispherical metal halides inside the metal oxide film. It was assumed that the electrochemical noise occurs owing to the formation of halide nuclei in the passive film, prior to pitting corrosion. From the stochastic analysis a distribution function was obtained for the size of the halide nuclei that form inward into the passive film. The survival probability of pit initiation, the specific parameter of pitting corrosion, was calculated as a function of time, and good correspondence was obtained with the reported experimental results. Also, the noise level was determined as the uncertainty of the distribution function for the radii of the halide nuclei. The calculated noise level was found to be appreciable and can then cause the electrochemical noise during the induction time.