Technical note Effects of dodecylamines on electrochemical impedance spectra of iron at corrosion potential in sulphuric solutions with and without addition of chloride

Abstract

The electrochemical impedance spectra (EIS) of iron at its corrosion potential in 0·5M H₂SO₄ solutions, with and without addition of various concentrations of dodecylamine (DDA), were investigated. The features of the solutions with added DDA were similar to those of the blank solution, but with DDA in the presence of a 0·1 mol L⁻¹ concentration of chloride ions the EIS degenerated to a single capacitive arc with much larger transfer resistance, which corresponds to a much higher inhibition efficiency. The results of corrosion potential and polarisation measurements show that the inhibition of corrosion of iron in H₂SO₄ solution by DDA is caused by the geometric blocking effect of the adsorbed species, irrespective of the presence of chloride. The measured EIS are consistent with a theory describing faradaic admittance at mixed potential with geometric blocking.

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