In situ SR-XRD analysis of corrosion product formation during 'pseudo-passivation' of carbon steel in CO2-containing aqueous environments.

In situ Synchrotron Radiation X-ray Diffraction (SR-XRD) is employed to follow the evolution of corrosion products on X65 carbon steel in a CO 2 -containing aqueous environment (80 °C, pH 6.3–7.3). A custom-designed flow cell is used to follow the real-time concomitant changes in electrochemical behaviour and corrosion product growth during stages of both natural and potentiodynamically driven 'pseudo-passivation'. We show that no detectable crystalline magnetite (Fe 3 O 4) phase forms during 'pseudo-passivation' across all conditions studied. Furthermore, the results suggest the significant ennoblement observed during 'pseudo-passivation' in these experiments can be strongly related to the accumulation of iron carbonate (FeCO 3) on the steel surface. • Surface layers play a key role in pseudo-passivation of carbon steel. • Synchrotron radiation XRD employed in-situ with electrochemical techniques. • Investigation at 80 °C, in pH range from 6.3 to 7.3 in CO 2 environments. • Pseudo-passivation strongly linked to wide coverage of X65 steel by iron carbonate. • Magnetite (Fe 3 O 4) was not detected by SR-XRD under these conditions. [ABSTRACT FROM AUTHOR]