The effects of rain water and so2 gas on the coating performance and cut-edge corrosion of some organic-coated metallic materials

In this study, the effect of S02 gas on the atmospheric corrosion of (polyester, epoxy and polyurethane) coated galvanized steel and cut-edge substrates in different relative humidities was investigated. For this purpose the substrates were subjected to SO2 gas for 20, 40 and 60 days in test cells with adjusted relative humidities 70%, 80%, 90% and 100%. In addition, samples of organic-coated galvanized specimens and cut-edge 120, 150 and 180 days were exposed to the effects of artificial acid rain solution. After that the effects of SO2 and artificial acid rain solution on the atmospheric corrosion of organic-coated galvanized steels exposed to corrosive media was investigated using electrochemical impedance spectroscopy (EIS), anodic polarization curves and linear polarization resistance (LPR) measurement techniques. Nyquist diagrams were interpreted by using ZView program.It was seen that organic samples which exposed to generally relative humidities (RH) of 70% experienced minimum degradation, whereas the samples lost their protection behaviour significantly under relative humidities of 80%, 90% and 100%. Two different electrical equivalent circuits were proposed in order to evaluate the Nyquist diagrams that obtained these relative humidities.