The electrochemical noise of mild and stainless steel in various water solutions

Abstract

The results of electrochemical noise measurements are described and compared with the results of corrosion measurements from various reference methods. Voltage- and current-noise are correlated to the rates and the types of corrosion. The electrochemical-corrosion noise (ECN) probe consisted of three identical electrodes. The first pair formed a voltage source and the second pair a current source. Measurements were made on mild steel and on stainless steel in aqueous solutions of various pH and conductivity values. Two electrode surface areas were employed. It was observed that the higher amplitudes of voltage and current, as well as the number of their fluctuations, reflect higher corrosion rates. The average power-spectrum densities for electrochemical noise at various frequency intervals (from 1 mHz to 1 Hz) were calculated and compared with the results of the reference methods (visual inspection, SEM analyses, I vs E curves, electrical-resistance). A good correlation was obtained for current-noise with the reference methods ( P > 0.8), while correlation of potential-noise was worse. The difference between potential- and current-noise power-spectrum densities was found to be related to the type of corrosion. Current fluctuations are presumed to be the consequence of mass transport, while potential fluctuations are due to events on the electrode surfaces.