TITLE:
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
AUTHORS:
Thangaraj Balusamy, Toshiyasu Nishimura
KEYWORDS:
Epoxy Coated Carbon Steel, Alkaline Solution, Chlorides, SECM, Wet/Dry Corrosion Cycles
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.7 No.7,
June
30,
2016
ABSTRACT: 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 (Rf)
and charge transfer resistance (Rct),
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.