Power Spectral Density Analysis of the Corrosion Potential Fluctuation of Aluminium in Early Stages of Exposure to Caribbean Sea Water

Aluminium samples were exposed for six months to Carribean sea water. The fluctuations of the free corrosion potential values (E-corr at o.c.p.), considered as electrochemical noise, were correlated with the aluminium pitting corrosion in sea water, influenced by different crystalline phases formed on the metal surface: Al(OH)(3) as a corrosion product in pits, and likewise crystals of MgCaCO3 and SiO2 proceeding from the sea water. At three months the film of bio-fouling had grown on aluminium surface, formed by two diatoms (microalgae). E-corr fluctuation analysis was carried out using the power spectral density (PSD) vs frequency. The decrease of the PSD slopes (negative beta exponent) indicated a release of spontaneous energy during from the aluminium surface, with the progress of pit formation in sea water. The calculated Hurst exponent values suggested that pits formed randomly on the surface in sea water could be as a consequence of highly persistent processes, dominated by fractional Gaussian noise (fGn) at almost all periods of testing in sea water, with the contribution of fractional Brownian motion (fBm) during some periods of time.