Determination of Corrosion Properties of Lacquered Tinplate in Citrate Solutions by DC and AC Electrochemical Methods

The present investigation has been carried out to determine the usefulness of direct current (DC) and alternating current (AC) electrochemical methods for corrosion monitoring of unlacquered and lacquered tinplate samples. Evaluation was performed with 5-µm and 7-µm coatings of an epoxy-phenolic lacquer in citrate buffer solution, pH=4⁠. The steady-state corrosion conditions for these epoxy-phenolic lacquers were established after 8 to 10 days of accelerated corrosion at 37°C. Electrochemical impedance spectroscopy (EIS) was used to obtain R_p in the Stern-Geary equation. The data indicate that the corrosion rate in the cans is completely due to the tin dissolution process. For the electrolytes chosen for this study, the iron content of the solution was found to be very low. l_corr values were obtained by DC and AC methods and the results agreed well.