Analysis of Electrochemical Current Noise From Metastable Pitting of SS304L in NaCl Solutions

Electrochemical noise emanating from a corrosion situation gives indication about the nature and form of corrosion. An attempt has been made to analyse electrochemical current noise signal generated under potentiostatic condition (for metastable pitting) for SS304L–NaCl system. To begin with polarisation plots of SS304L were obtained in various test solutions to precisely know pitting potential of SS304L. It is found that E_pit and i_pass increase on increasing chloride content. The electrochemical current noise was measured at potentials 20–30 mV below the pitting potentials. The current time record shows two types of current transients; (i) slow rise and rapid decay and (ii) rapid rise and slow decay. Power spectral density analysis of current noise shows that the power (A²/Hz) of the signal measured at metastable pitting range increases with increasing chloride. Sampling frequency has to be properly selected otherwise some of the spikes are not recorded and as a result, size and shape of few current transients is altered.