Electrochemical noise resistance as a tool for corrosion rate prediction

Current and potential fluctuations (electrochemical noise [EN]) between two nominally identical carbon steel electrodes were recorded in a solution of sodium phosphate (Na3PO4) at different concentrations. After passivation was reached, pitting was induced by addition of chlorides. Data were collected with different sampling rates. Linear polarization resistances (LPR) also were measured. Electrochemical signals were transposed in the frequency domains using the fast Fourier transform. Statistical parameters from the signals in the time and in the frequency domains were compared with corrosion rates (V-c) as measured by LPR. Noise resistance (R-n) also was calculated. From standard deviation (sigma) values of the current and potential noises, pitting attack was revealed at its onset. Good correlation between data from the different techniques was found. R-n gave values proportional to the polarization resistance (R-p). The issue of how sampling rate can affect EN data collection also was addressed.