Power Spectral Density Analysis of the Corrosion Potential Fluctuation of Stainless Steel 316L in Early Stages of Exposure to Caribbean Sea Water

Wednesday, 27 May 2015: 09:25
PDR 2 (Hilton Chicago)
C. Espinosa, L. P. Veleva, and J. L. Lopez (CINVESTAV, Merida, Applied Physics Department)
Stainless Steel 316 L samples were exposed for one month to Caribbean sea water. The fluctuations of the free corrosion potential values (Ecorr at o.c.p.), considered as electrochemical noise (EN), were correlated with the stainless steel pitting corrosion in sea water. Ecorr fluctuation analysis was carried out using the power spectral density (PSD) vs frequency. Figure 1 presents the initially changes of Ecorr with time vs frequency in bilogarithmic scale. For the first three days, the PSD slopes present a negative β exponent (β > 1) at lower frequencies [0.002 – 0.05 Hz], indicating a release of spontaneous energy from the steel surface (corrosion). However, at major frequencies β tends to values close to zero (0.12 – 0.07). At later stages the PSD slopes show a unique value close to zero (0.02 – 0.06), in all range of frequencies [0.002 – 1 Hz]. The exponent β is associated with persistent processes (forces) in data series (216) over time. The calculated Hurst coefficient based on β values suggested that initially the localized corrosion process occurs with the contribution of fractional Brownian motion (fBm) and fractional Gaussian noise (fGn). After the first three days, the Ecorr fluctuations were only dominated by fGn (H≈0.5), which corresponds to the special case when the corrosion occurs at the border between anti-persistent (H<0.5) and persistent (H>0.5) processes. The Ecorr fluctuations were correlated with the data surfaces provided by SEM-EDS and XRD.