Dopant Effects in Polyaniline Inhibition of Corrosion-Driven Organic Coating Cathodic Delamination on Iron

Williams, Geraint; Gabriel, Andreas O.; Cook, Anthony; McMurray, H. N.

doi:10.1149/1.2229280

Cited by 71 publications

(71 citation statements)

References 48 publications

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“…It seems that even though PANI coating exists on Mg alloy surface, if the regular dissolution-precipitation reaction cannot be suppressed, a poor corrosion resistant product layer forms on Mg surface and further corrosion continues. A similar suggestion was also reported by Holness et al 50 and Williams et al 51 in the studies of the oxide layer growth at the PANI/iron interface, where the PANI-induced layer did not show a good protective performance and so thickened linearly with time in humid atmosphere. They attributed the poor corrosion resistance to the PANI, acting as a hydrous polyelectrolyte with a redox couple of polarizing.…”

Section: C301supporting

confidence: 85%

Growth Behavior of Initial Product Layer Formed on Mg Alloy Surface Induced by Polyaniline

Luo

Wang

Guo

et al. 2015

J. Electrochem. Soc.

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The quality of the interfacial protective layer induced by polyaniline (PANI) has been claimed to play a crucial role for the enhanced corrosion protection of Mg alloy, but its growth behavior is not well understood. Here some composition, structure and growth kinetics of the protective layer formed at the PANI-emeraldine base (EB) coating/AZ91D Mg alloy interface were investigated to explore the growth mechanism. Upon immersion in 0.5 M NaCl solution, the growing interface layer under EB coating exhibited a fast passivation rate and an increased corrosion resistance, which was largely influenced by ion concentration. XPS depth profiles showed that the EB-induced layer was a mixture of MgO and Mg(OH) 2 , in which no significant bi-layer structure existed and MgO was dominant throughout the bulk film. These observations suggest that the interaction between EB and Mg can promote the faster growth of a stable MgO-rich layer mixed with Mg(OH) 2 probably by solid reaction. Meanwhile less hydration of MgO and dissolution-precipitation reaction occur, thus leading to less Mg(OH) 2 in the outer layer. Magnesium alloys have drawn great attention in automotive and aerospace industry due to their excellent properties such as low density and high specific strength. However, limited corrosion resistance of such alloys has retarded their widespread applications. To improve the corrosion resistance of Mg alloys, numerous coating techniques have been explored, among which organic coating containing corrosion inhibiting pigments is an economical and effective method in industry. One important pigment for Mg alloys is polyaniline (PANI) including emeraldine salt form (ES) and emeraldine base form (EB). 1-6Its highly efficient corrosion-protection performance for Mg alloys has been shown to be competitive to a chromate-pigmented coating. Additionally, self-healing capability was also found on a hybrid solgel/PANI coated Mg alloy upon immersing in Harrison's solution, where no pitting or filiform corrosion occurred around the scratched area while a protective layer was formed.8 Sathiyanarayanan et al. 1 and Wang et al. 8 observed that, after an initial decrease upon immersion in corrosive electrolytes, the complex impedance of PANI coated Mg alloy recovered, which was attributed to the formation of a protective layer. The different chemical composition on the EB-induced protective layer surface was already confirmed by X-ray photoelectron spectroscopy (XPS) in comparison with that formed underneath a varnish coating. 2,6The mechanism of PANI promoting a protective layer formation has been mostly supported by extensive studies in various metal systems.9-14 Nevertheless, few works have been done to understand the protective layer growth behavior. The most intractable issue of how the interaction between PANI and metal induces the protective layer growth still remains unsolved.9 This is attributed primarily to the great difficulty in in-situ investigation on the growth kinetics of interfacial layer formed beneath a coating. Electroche...

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Section: C301supporting

confidence: 85%

Growth Behavior of Initial Product Layer Formed on Mg Alloy Surface Induced by Polyaniline

Luo

Wang

Guo

et al. 2015

J. Electrochem. Soc.

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“…The pK a values for H 2 PP are 2.3 and 7.8. 25 The deprotonation equilibria for H 2 incorporating H 2 PP in the same conditions, the HPP − species would be prevalent, according to the pk a value given in Reaction 7. As such, it is expected that PP 2− levels would be insufficient to form a solid film despite the level of Zn 2+ ions.…”

Section: Resultsmentioning

confidence: 99%

Inhibition of Localized Corrosion of Hot Dip Galvanized Steel by Phenylphosphonic Acid

Glover

Williams

2017

J. Electrochem. Soc.

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Phenylphosphonic acid (H 2 PP) is investigated as a corrosion inhibitor of hot dip galvanized steel (HDG) fully immersed in a 5% (w/v) sodium chloride electrolyte. An in-situ Scanning Vibrating Electrode Technique (SVET) is used where concentrations of H 2 PP are systematically added to the electrolyte in neutral conditions. H 2 PP, at a concentration of 5 × 10 −2 mol dm −3 , is shown to effectively inhibit localized corrosion over a 24 h period with 96% efficiency. H 2 PP is compared with a sodium phosphate (Na 3 PO 4 ) inhibitor at the same concentration over a wide pH range. With current legislative pressure to eliminate Cr(vi)-based inhibitors from protective coating formulations, there is a pressing need to identify effective, environmentally-friendly alternatives. Chromatefree passivation treatments have been studied extensively 1-4 and the most widely used alternative to chromate is a phosphate passivating treatment. Such a system facilitates the precipitation of protective zinc compounds via the supply of soluble anions that react with the zinc ions generated in metal dissolution.5 A phosphate passivation treatment generates a Zn 3 (PO 4 ) 2 barrier to inhibit the anodic process, 4,5 the formation of which can act to extend the pH stability of the surface layer down to values of around pH 6. However, as zinc phosphates are 1000 times more soluble than Cr (III), inferior corrosion inhibition performance is observed. 7 The corrosion of a zinc surface generates a wide range of pH zones, whether in bulk electrolyte conditions, atmospheric conditions or, most notably, under a water droplet. 8,9 Corrosion-driven cathodic coating delamination phenomena produces an alkaline underfilm environment where values of pH 10-11.5 have been recorded previously on a coated zinc surface. 10In order to compete with an adsorbed chromium (III) oxide layer, an effective corrosion inhibitor system would have to be stable in a range of pH 4-14.7 It is therefore of great importance to examine potential chromate replacement inhibitors in non-neutral conditions.In a recent Scanning Kelvin probe study, we showed that in-coating additions of H 2 PP increased the initiation time for underfilm cathodic coating delamination by up to 20 h and reduced the delamination rate by up to 94% on hot dip galvanized steel (HDG) surfaces.11 An 'etch' effect was shown to be the dominant inhibition mechanism, whereby a reaction occurs at the point of first contact of the wet coating with the substrate producing an interfacial metal phosphate salt layer. We hypothesize that a second mode of inhibition occurs whereby the leaching of dissociated PP 2− ions from the coating into the substrate/coating interface forms a ZnPP layer, blocking the anodic reaction. H 2 PP has been shown previously to strongly adsorb onto surface oxide films, disfavoring chloride.12 The principal aim of this work is to determine the efficiency of H 2 PP as an inhibitor for HDG surfaces in bulk immersion conditions. The localized corrosion activity occurring over a commercial gr...

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“…A large number of polymers owe their self-repair properties to the corrosion-inhibiting compounds introduced into the matrix, such as silyl ester (octyldimethylsilyloleate), 8-hydroxyquinoline, calcium(II) and zinc(II)-exchanged pigments, phenylphosphonic acid and sodium benzoate [12,13,[24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Self-healing coatings in anti-corrosion applications

2013

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Nonmetallic (based on polymers or oxides) and metallic protective coatings are used to protect metal products against the harmful action of the corrosion environment. In recent years, self-healing coatings have been the subject of increasing interest. The ability of such coatings to self-repair local damage caused by external factors is a major factor contributing to their attractiveness. Polymer layers, silica-organic layers, conversion layers, metallic layers and ceramic layers, to mention but a few, are used as self-healing coatings. This paper presents the main kinds of self-healing coatings and explains their selfhealing mechanisms.

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Dopant Effects in Polyaniline Inhibition of Corrosion-Driven Organic Coating Cathodic Delamination on Iron

Cited by 71 publications

References 48 publications

Growth Behavior of Initial Product Layer Formed on Mg Alloy Surface Induced by Polyaniline

Growth Behavior of Initial Product Layer Formed on Mg Alloy Surface Induced by Polyaniline

Inhibition of Localized Corrosion of Hot Dip Galvanized Steel by Phenylphosphonic Acid

Self-healing coatings in anti-corrosion applications

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