Crevice corrosion studies using electrochemical noise measurements and a scanning electrode technique

The formation of crevice corrosion on type 304L stainless steel when immers ed in 0.05 M ferric chloride solution has been used to investigate electroc hemical potential noise measurements. The surface activity of the stainless steel was simultaneously studied using a scanning electrode technique to p rovide corroborating evidence of crevice corrosion. The spontaneous potenti al noise fluctuations were recorded in a freely corroding system with respe ct to a reference electrode. Power spectral densities calculated by fast Fo urier transforms and a stochastic technique were used for the analysis of t he time records, in order to reveal fundamental characteristics of the fluc tuations resulting from the initiation and propagation of crevice corrosion . A stochastic analysis tool based on a Poisson-process test has been devel oped and evaluated using data generated by computer simulation of both stoc hastic and deterministic processes, before applying the analysis technique to real corrosion processes. There appears to be agreement between the two analysis methods; both revealed the presence within the time series of stoc hastic and deterministic features. Using a combination of noise analysis te chniques it was possible to obtain evidence of the different corrosion proc esses occurring on the 304L stainless steel which were metastable pitting, propagation and termination of localized corrosion events, and the developm ent of crevice corrosion. (C) 2000 The Electrochemical Society. S0013-4651( 99)08-125-2. All rights reserved.