The corrosion behavior of carbon steel/acryl film/electrolyt system

Abstract

The corrosion behaviour of carbon steel coated with acryl film was investigated by electrochemical measurements (electrochemical impedance spectroscopy, anodic stepwise polarisation) as a time function of immersion in 3% NaCl solution. Analysis of Nyquist and Bode diagrams with the Boukamp Programme established two electrical equivalent circuits for the simulation of the carbon steel corrosion under this organic film. For short exposure periods, the corrosion process can be modelled with two time constants, but, after 10 days of immersion, only four time constants can describe the carbon steel/acryl film/electrolyte system. The water and ions permeability of the acryl film Was estimated from the time dependence of its electrical capacitance and resistance calculated with the electrical equivalent circuit with four time constants. The correlation of these results with those obtained from the anodic polarisation curves (electrochemical parameters, porosity, effciency) permited to establish the probable sequence of the carbon steel corrosion under the acryl film; the controlling rate step is the ionic transport through the film.