In this paper, the semiconducting behavior of No.20 carbon steel coated with different polymer coating in 5‰ sulfuric acid solution was studied by utilizing potential-capacitance and Mott-Schottky analysis. It showed that in the same testing condition, the phenol aldehyde resin and epoxy resin showed n-type semiconducting behavior in 5‰ sulfuric acid, whereas for the alkyd resin, it showed p-type semiconducting behavior in 5‰ sulfuric acid solution. It was suggested that the space charge layer of the polymer coating in 5‰ sulfuric acid solution might be asymmetry. It was suggested that at the early stage of immersion, the polymer coating behaved as an insulator, with increasing immersion time, the coating transferred to P-type semiconductor, then to N-type semiconductor.
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