Conducting Polymers and Corrosion III. A Scanning Vibrating Electrode Study of Poly(3-octyl pyrrole) on Steel and Aluminum

Abstract

Electroactive conducting polymers (ECPs) continue to be of considerable interest as components of corrosion‐resistant coating systems. ECPs, in addition to being conductive, are redox active materials, typically with potentials that are positive of iron and aluminum. Thus, as with chromate, interesting and potentially beneficial interactions of ECPs with active metal alloys such as steel and aluminum are anticipated. In this work, the scanning vibrating electrode technique (SVET), also known as the current density probe, was used to probe such interactions between a poly(3‐octyl pyrrole) coating (POP) and cold‐rolled steel and aluminum (Al 2024‐T3) substrates. The POP coatings were scribed to simulate a defect through the coating to the metal substrate surface. The SVET was used to map the current flowing in and around the defect while the sample was immersed in either 3% NaCl (steel) or in dilute Harrison solution (aluminum), an aqueous solution consisting of 0.35% false(NH4)2SO4 , 0.05% NaCl. Although there were significant differences in the behavior of the POP‐coated steel and POP‐coated aluminum substrates, both exhibited a significant delay before the onset of any observable current compared to uncoated or epoxy‐coated samples. Current density maps for the steel clearly indicate that the reduction reaction occurred on the conducting polymer surface, with oxidation confined to the defect. Current density maps for the aluminum alloy never displayed significant oxidation at the defect. Rather, reduction (after a significant delay) occurred at the defect as well as across the polymer surface, with concomitant localized undercoating oxidation of the aluminum substrate. © 2000 The Electrochemical Society. All rights reserved.

Direct Electrodeposition of Polypyrrole on Aluminum and Aluminum Alloy by Electron Transfer Mediation

“…Film characterization by AFM and SEM.- Figure 5 provides a comparison of the AFM images for the bare Al 2024-T3 alloy surface ͑prepared as described earlier͒, for a solvent-cast poly͑3-octyl pyrrole͒ ͑POP͒ film, 6 and for the galvanostatically deposited Ppy/ Tiron and Ppy/pTS films. The bare alloy displays a surface roughness consistent with a 600 grit polish.…”

Layers of Inhibitor Anion – Doped Polypyrrole for Corrosion Protection of Mild Steel

“…Reaction (2) takes place within the defect as well as on PPy film if Ppy is conductive and can mediate the electron transfer [31,32]. The dopant anions DOP nform insoluble salts or complexes [Fe x O y (DOP)] with iron ions and can prevent further corrosion.…”

Magnesium-Based Sacrificial Anode Cathodic Protection Coatings (Mg-Rich Primers) for Aluminum Alloys

“…A non-chrome/chrome replacement coating system would need to extend the life of existing Al-based assets and facilitate expanded use of economical aluminum alloys in both DoD and commercial applications [31]. Consequently, extensive research has been conducted in search of alternative technologies, such as anodization [32], sol-gel treatment [33][34][35], pigmented coatings [36], plasma polymer layers [37], conductive pigments/polymers [38,39], and pigment-based cathodic protection [40].…”