Effects of Sodium Phosphate and Sodium Nitrite on the Pitting Corrosion Process of X70 Carbon Steel in Sodium Chloride Solution

• Main Authors: Yongyan Zhu, Jiayi Ding, Jianli Zhang, Liang Li
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Materials
• Subjects: corrosion inhibitor; pitting corrosion; anodic dissolution; scanning electrochemical microscope (SECM); carbon steel
• Online Access: https://www.mdpi.com/1996-1944/13/23/5392

In this paper, effects of sodium phosphate (Na₃PO₄) and sodium nitrite (NaNO₂) on the pitting corrosion of X70 carbon steel in 0.10 mol/L NaCl solution were investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) method, scanning electron microscope (SEM) and scanning electrochemical microscope (SECM). The SECM equipment was used to observe the dynamic processes of the pitting corrosion in situ. Na₃PO₄ or NaNO₂ in the sodium chloride solution decreased the local anodic dissolution and increased the pitting resistance of the specimen. By analysis and comparison, it can be concluded that the inhibition effect of Na₃PO₄ is mainly due to the formation of a salt film, while the corrosion inhibition of NaNO₂ is principally attributed to a protective oxide film on the electrode surface.