A New Electrochemical Noise Technique for Monitoring the Localized Corrosion of 304 Stainless Steel in Chloride - Containing Solutions

A new electrochemical noise technique was developed to investigate metastable pitting by applying a bias potential between two nominally identical working electrodes. The current flowing between the biased working electrodes was measured with a zero resistance ammeter. Potential was measured between one working electrode and a reference electrode. These tests were conducted using 304 stainless steel working electrodes in a 0.5 M NaCl + borate buffer solution. A bias potential of 150 to 200 mV was used to localize the anodic and cathodic reactions to their respective electrodes. The noise signal was significantly affected by conditioning the electrodes at open circuit. When the electrodes were conditioned for several days, the breakdown potential increased, and the frequency and magnitude of the current transients increased. However, when the conditioning time was increased to a month, all metastable pitting transients disappeared, indicating an enhanced passive film.