Author(s)

Thangaraj Balusamy, Toshiyasu Nishimura^*

Corrosion Resistant Steel Group, Research Center for Structural Materials (RCSM), National Institute for Materials Science, Tsukuba, Japan.

The present work is investigated the in-situ monitoring of local corrosion process of scratched epoxy coated carbon steel in saturated Ca(OH)₂ with and without 3% NaCl using SECM and correlated with EIS. The results obtained from EIS analysis showed that the corrosion resistance of scratched epoxy coated carbon steel decreases in Cl^- containing solution as the increase in wet/ dry corrosion cycles. This was indicated by decrease in film resistance (R_f) and charge transfer resistance (R_ct), while the coated steel maintain the resistance values in saturated Ca(OH)₂, most of which recovered after drying. The corrosion process was monitored using SECM by setting the tip potential at -0.70 V vs Ag/AgCl, where the consumption of dissolved oxygen occurred at the surface of test sample. The consumption of dissolved oxygen current (I’_oxy-c) values was increased during the immersion in a solution with 3% NaCl. However, in wet/dry corrosion cycles, I’_oxy-c was decreased due to the coverage of hydroxides/oxides at scratch area which suppressed the consumption of dissolved O₂. It was found that the continuous decrease in corrosion was mainly attributed to continuous formation of corrosion products at anodic spots.

Epoxy Coated Carbon Steel, Alkaline Solution, Chlorides, SECM, Wet/Dry Corrosion Cycles

Balusamy, T. and Nishimura, T. (2016) In-Situ Corrosion Monitoring of Scratched Epoxy Coated Carbon Steel in Saturated Ca(OH)₂ with or without 3% NaCl by Scanning Electrochemical Microscopy and Electrochemical Impedance Spectroscopy. American Journal of Analytical Chemistry, 7, 533-547. doi: 10.4236/ajac.2016.77049.