Corrosion Inhibition in CO₂-Saturated Brine by Nd³⁺ Ions

This study reports the use of an inorganic corrosion inhibitor to mitigate dissolved CO₂-induced corrosion. Using electrochemical techniques (polarization curves, open circuit potential, polarization resistance, and electrochemical impedance), the effect of adding Nd³⁺ ions on the corrosion resistance of X52 steel immersed in CO₂-saturated brine at 20 °C and 60 °C was evaluated. The polarization curves showed that the Icorr values tend to decrease with increasing Nd³⁺ ion concentration, up to the optimal inhibition concentration, and that the corrosion potential increases at nobler values. Open circuit potential measurements showed a large increase in potential values immediately after the addition of the Nd³⁺ ions. Similarly, polarization resistance measurements showed similar trends. It was observed that regardless of temperature, Nd³⁺ ions can reduce the corrosion rate by more than 97% at doses as low as 0.001 M. Electrochemical impedance measurements confirmed the formation of a protective layer on the steel surface, which caused an increase in the magnitude of the impedance module and phase angle, which indicates an increase in the resistance to charge transfer and capacitive properties of the metallic surface. The characterization of the metallic surface showed that the protective layer was formed by Nd carbonates, whose formation was due to a CO₂ capture process.