Electrochemical polarization measurements have been used to examine the corrosion of carbon steel by aqueous CO2 at partial pressures from 0 to 1.4 MPa in rotating disk and static electrode cells at 25°C. A detailed corrosion mechanism was derived which consisted of four redox reactions under varying types of kinetic control: diffusion controlled reduction of H+ (aq) to H2 (g), chemically controlled reduction of H2CO3° (aq) to H2 (g), charge transfer controlled reduction of H2O to H2 (g), and charge transfer controlled oxidation of Fe to Fe++. The rate of H2CO3° (aq) reduction was controlled by the rate of a preceding chemical reaction in which CO2 (aq) is homogeneously hydrated to H2CO3° (aq). The corrosion rate, Tafel constants, and exchange current densities were determined from an electrochemical model of the polarization curves, based on mixed potential theory. Polarization curves at 100°C suggest that a similar reaction mechanism may be occurring at higher temperatures and that the corrosion rate is significantly higher.

Subject
Electric current, Corrosion rate, Diffusion, Corrosion reactions, Polarization curves, Constants, Carbon dioxide, Carbon steel, Corrosion mechanisms, Risk reduction, Chemical reactions, Electrodes, Corrosion potential
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1989
Association for Materials Protection and Performance (AMPP)
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