Breakdown of the iron passive layer by use of the scanning electrochemical microscope

• Published in: Journal of the Electrochemical Society Vol. 144; no. 8; pp. 2657 - 2665
• Main Authors: STILL, J. W, WIPF, D. O
• Format: Journal Article
• Language: English
• Published: Pennington, NJ Electrochemical Society 01.08.1997
• Subjects: Applied sciences; Corrosion; Corrosion mechanisms; Exact sciences and technology; Metals. Metallurgy; Phosphates; Corrosion; Scanning probe microscopy; Electrochemical method; Citrate; Transition metal; Iron; Buffer solution; Disk electrode; Passivation; Passivity breakdown; Surface structure
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1837879

The scanning electrochemical microscope (SECM) is used to generate localized corrosion at passivating iron surfaces by using the tip to generate Cl exp - ions. Use of the SECM allows the rapid establishment of a locally aggressive chemical environment at a preselected site on the iron surface. The susceptibility for passive layer breakdown and corrosion initiation was examined as a function of the time between the start of the passive layer growth and the formation of Cl exp - ions. The breakdown of the passive layer was found to depend strongly on the passivation potential and the site of Cl exp - formation on the iron surface. In addition to generating Cl exp - ions, the SECM tip was simultaneously used to detect large iron ion concentration fluctuations as corrosion began. Current fluctuations at the tip were observed and ascribed to precursors to the passive layer breakdown.