AN ELECTROCHEMICAL BEHAVIOR OF CO2 CORROSION OF STATIC CARBON STEEL ELECTRODE IN PRESENCE OF ACETIC ACID, ACETATE AND METAL INHIBITOR (Zn^2+, Ca^2+) USING AC AND DC ELECTROCHEMICAL TECHNIQUES

Abstract

AC and DC electrochemical techniques: electrochemical impedance spectroscopy (EIS), and (Potentio-dynamic), electrochemical corrosion measurements are conducted on static carbon steel electrode at room temperature in 3.5% NaCl Solution, bubbled with 1 atm CO2, or 1 atm. N2, or air exposed test solution. Different chemicals; e.g. (acetate, sodium acetate, acetic acid, sodium sulphate, calcium chloride and zinc chloride) were added to test solution. The results of polarisation curves are compared with impedance measurements results to understand the mechanism of the corrosion process. And take the benefits of the comparison to understand more the physical meaning of AC corrosion data. The results of polarisation curves suggest that CO2 makes a large contribution in the corrosively of all solutions. However, in the presence of acetic acid the solutions were found to be corrosive even in the absence of CO2, and this can strongly attributed to the pH. The impedance results confirm the mentioned findings; also there was a good agreement between AC (Impedance) and DC (Polarisation curves) results. Zinc and Calcium considered as metal ions inhibitors, DC and AC results suggest that, Ca^2+ in aerated solution may tends to forming (CaOH2) that gives more isolation for cathodic species (i.e. hinders the diffusion links leads to fresh metal surface). Regarding zinc ions the polarisation curves indicate that electrochemical behaviour of zinc in terms passivity, depends strongly on the electrode potential.