Electrochemical properties of iron dissolution in the presence of CO2- Basics Revisited.
Srdjan Nesic, Nicolas Thevenot, Jean-Loius Crolet and Dragutin M. Drazic.

In order to shed more light on the anodic reaction mechanism in CO2 corrosion of mils steel , two different kinds of electrochemical measurements were used : potentiodynamic sweep and galvanostatic measurements. Experiments were conducted in a glass cell at room temperature (T=22+_ 1 C), different CO2 partial pressures (0-1 bar), over a broad pH range (2-7) using a rotating cylinder at 4000 rpm.
Distinct and different anodic mechanisms were observed for pH<4 and for pH>5. In the intermediate area there seems to be a transition from one mechanism to another. New orders of reaction and tafel slopes were extracted, very different from what was previously assumed. A coherent ensemble of mechanisms was proposed for the anodic reaction, which is consistent with the experimental results.

Consequences of the present findings for the CO2 corrosion area are discussed. For example, in case of undissolved iron carbide layers, it is no longer possible to discriminate the roles of galvanic coupling and internal acidification.

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