Interpretation of Electrochemical Noise Signals Arising from Symmetrical and Asymmetrical Electrodes Made of Polypyrrole Coated Mild Steel

This article applies the standard deviation of partial signal (SDPS) plots of electrochemical noise (EN) current signals originating from corrosion events on the symmetrical and asymmetrical electrodes made of uncoated and polypyrrole (PPy)-coated mild steel alloy in 4000 ppm NaCl+1000 ppm NaNO2 solution. Signal recording was performed after 30, 60, 90 min and 24 h from immersion time. Two types of symmetrical electrodes were made from uncoated (Bare-Bare) and PPy coated (PPy-PPy) mild steel electrodes. The asymmetrical electrodes (PPy-Bare) prepared from a difference in the coating between two working electrodes which are otherwise identical. The time records and the corresponding SDPS plots obtained from the three types of systems show an increase in the amplitude and the time width of EN current transients with movement from Bare-Bare to PPy-PPy. Therefore, the corrosion severity increases with movement from Bare-Bare to PPy-PPy. Over time from 30 min to 24 hours‚ the PPy coating in the Bare-PPy configuration is early insulated compared to the PPy-PPy. It seems that the symmetrical configuration (Bare-PPy) is the suitable system for evaluating the corrosion protection of PPy coatings by EN technique.