Determination of Iron Valence States Around Pits and the Influence of Fe³⁺ on the Pitting Corrosion of 304 Stainless Steel

• Main Authors: Hao Zhang, Nan Du, Shuaixing Wang, Qing Zhao, Wenjie Zhou
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Materials
• Subjects: stainless steel; pitting corrosion; chromogenic method; fe3+ reduction
• Online Access: https://www.mdpi.com/1996-1944/13/3/726
• ISSN: 1996-1944

Potassium ferricyanide and potassium ferrocyanide were used to observe and monitor the pitting corrosion of 304 stainless steel (SS) at anodic polarization in situ. The results show that there are Fe³⁺ ions around the corrosion pit when pitting occurs on 304 SS in NaCl aqueous solution. The effect of Fe³⁺ surrounded pits on the pitting corrosion was also studied by testing the electrochemical behavior of 304 SS in different Fe³⁺/Fe²⁺ solutions. The presence of Fe³⁺ leads to the positive shift of corrosion potential and the increase of corrosion rate of 304 SS. There are two possible reasons for this phenomenon. On the one hand, Fe³⁺ hydrolysis results in the decrease of pH value of solution. At the same iron ion concentration, the higher the Fe³⁺ ion concentration, the lower the solution pH value. On the other hand, Fe³⁺ may reduce on the electrode surface. The decrease of solution pH and the reduction of Fe³⁺ resulted in the acceleration of the corrosion rate.