Formation of protective surface films on carbon steel in mildly alkaline aqueous alkanolamine CO2 solutions

Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements, complemented by solution speciation predictions and ex situ surface analyses, were used to investigate film formation on carbon steel in CO2 saturated methyldiethanolamine(aq) solutions at 80 degrees C, pH 7.9-8.6. Pure FeCO3 films, evidenced by OCPs of ca. -0.5 to -0.4 V (SHE), were formed under anoxic conditions and provided corrosion protection to the underlying substrate, increasing charge transfer resistances tenfold. O2 ingress caused a positive OCP shift to ca. > +0.35 V (SHE), resulting in formation of traces of iron oxide at the interface, which was less protective.

Automated summary

In this study, electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements were used to investigate film formation on carbon steel in CO2 saturated methyldiethanolamine(aq) solutions at 80 degrees C, pH 7.9-8.6. Pure FeCO3 films were formed under anoxic conditions, providing corrosion protection to the substrate, while O2 ingress resulted in the formation of iron oxide at the interface, which was less protective.