The effect of oxygen partial pressure on the filiform corrosion of organic coated iron

• Published in: Corrosion science Vol. 89; pp. 46 - 58
• Main Authors: Watson, T.M., Coleman, A.J., Williams, G., McMurray, H.N.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-12-2014; Elsevier
• Subjects: A. Iron; A. Organic coatings; A. Steel; Applied sciences; C. Atmospheric corrosion; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy; Nonmetallic coatings; Production techniques; Surface treatment; A. Organic coatings; A. Iron; C. Atmospheric corrosion; A. Steel; Partial pressure; Filiform corrosion; Non metal coating; Surface treatment; Organic compounds; Atmospheric corrosion
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2014.08.004

•A tool has been developed to gain mechanistic understanding of filiform corrosion.•The apparatus allows control of the environment surrounding the head/tail region.•A ring of corrosion products is formed due to oxygen diffusion through the coating.•Step-wise filament growth suggests an electro-osmotic mechanism for advancement.•Disbondment of the coating by the anterior ring is not rate determining for growth.
An in-situ time-lapse optical microscopy study, using a novel dual-compartment cell is used to gain mechanistic understanding of filiform corrosion (FFC) affecting an organic-coated iron surface. The apparatus allows independent control of environments surrounding the filament head and tail regions. When oxygen-containing environments surround the filament head, an anterior cathodic arc is formed, constraining the filament head electrolyte. When oxygen is removed from the vicinity of the head, FFC propagation rates remain unchanged, although the constraining arc is not present. Maximum propagation is observed when oxygen is available for transport through the filament tail to the rear of the head.