Sweet Corrosion Inhibition by CO₂ Capture

The most practical and economical way to combat the problems derived from CO₂ corrosion (sweet corrosion) is the use of corrosion inhibitors of organic origin. Its main protection mechanism is based on its ability to adsorb on the metal surface, forming a barrier between the metal surface and the aggressive medium. However, despite its excellent performance, its inhibition efficiency can be compromised with the increase in temperature as well as the shear stresses. In this study, the use of an inorganic inhibitor is proposed that has not been considered as an inhibitor of sweet corrosion. The reported studies are based on using LaCl₃ as a corrosion inhibitor. Its behavior was evaluated on 1018 carbon steel using electrochemical measurements, such as potentiodynamic polarization curves, open-circuit potential measurements, linear polarization resistance measurements, and electrochemical impedance. The results showed an inhibition efficiency of the sweet corrosion process greater than 95%, and that the inhibition mechanism was different from the classic corrosion process in CO₂-free electrolytes. In this case, it was observed that the inhibitory capacity of the La³⁺ cations is based on a CO₂-capture process and the precipitation of a barrier layer of lanthanum carbonate (La₂(CO₃)₃).