Sweet Corrosion Inhibition by CO₂ Capture

Area of Science:

• Materials Science
• Electrochemistry
• Corrosion Engineering

Background:

• Organic corrosion inhibitors are common for CO₂ (sweet) corrosion but can be less effective at high temperatures and shear stresses.
• Their primary mechanism involves adsorption onto metal surfaces, creating a protective barrier.

Purpose of the Study:

• To investigate the effectiveness of lanthanum chloride (LaCl₃), an inorganic compound, as a novel corrosion inhibitor for sweet corrosion.
• To elucidate the specific inhibition mechanism of LaCl₃ on carbon steel in a CO₂ environment.

Main Methods:

• Electrochemical measurements including potentiodynamic polarization, open-circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy were employed.
• The study focused on 1018 carbon steel as the substrate material.

Main Results:

• LaCl₃ demonstrated an inhibition efficiency exceeding 95% for the sweet corrosion process.
• The inhibition mechanism was found to differ from traditional CO₂ corrosion inhibitors, involving CO₂ capture by La³⁺ cations.
• A protective barrier layer of lanthanum carbonate (La₂(CO₃)₃) was observed to precipitate on the metal surface.

Conclusions:

• Lanthanum chloride is a highly effective inorganic inhibitor for sweet corrosion on carbon steel.
• The unique mechanism involves CO₂ capture and lanthanum carbonate precipitation, offering a new strategy for corrosion control.