Electroactive Poly(aromatic amine) Films for Iron Protection in Sulfate Medium

Abstract

Polyaniline ͑PANi͒ and poly͑1,5-diaminonaphthalene͒ ͑PDAN͒ films can be deposited on iron from aqueous sulfuric acid. The films exhibit electroactive properties similar to those of PANi and PDAN generated on platinum. Electrosynthesis performed in the presence of both monomers leads to a composite film which presents excellent adhesion properties on iron. The composite film imparts a form of anodic protection for at least 9 days in pH 4 sulfate medium. Many corrosion control methods use coatings and conversion layers which contain toxic and environmentally hazardous materials, in particular, metal oxides such as chromate and phosphate. There is a great need to find a nontoxic replacement, and for the last 20 years, a great deal of attention has been devoted to organic polymers which could be used as primer coats. These polymers can be deposited on oxidizable metals by electropolymerization and are either insulating or conductive. The insulating coatings could act as diffusion barriers. [1][2][3][4][5] This is the case of poly͑phenylene oxide͒ type films studied in our laboratory.1-4 The ''functionalized polymer'' films obtained from phenol derivatives substituted by functional groups are strongly adherent on iron. They are reactive and constitute primary layers which permit the grafting of other protective layers, e.g., paints. Poly͑phenylene oxide͒ films present excellent protective properties but have the drawback of being too thin ͑thickness under 0.5 m, due to the insulating character͒.The thickness of inherently conductive polymers ͑ICP͒ is easily controlled when they are synthesized by the electrochemical method. ICP are electrically conductive owing to a system of conjugated double bonds. When deposited on iron, ICP could impart a form of anodic protection by maintaining the electrode in its passive state under aggressive conditions, in which the active passive layer alone would be destroyed in a few minutes.Among the ICP investigated for corrosion protection ͓polyaniline, 6-13 polypyrrole, 14-16 polythiophene, 17 poly͑5-amino-1-naphthol͒ 18 ͔, polyaniline has received the most attention. Nevertheless, the adhesion of electrosynthesized polyaniline films is generally quite poor.We have recently performed electropolymerization of naphthylamine derivatives bearing a functional group ͑-OH,-NH 2 ͒ on the second ring. It was demonstrated that polymerization occurred selectively via the -NH 2 group, leading to polyaniline-like films bearing a free -OH 18 or -NH 2 group in the chain. The presence of a functional group in the chain confers surface reactivity to the film which can be functionalized thereafter. In the case of 1,5-diaminonaphthalene ͑DAN͒ ͑Fig. 1͒, electroactive poly͑1,5-diaminonaphthalene͒ ͑PDAN͒ films ͑Fig. 1͒ were obtained, which can be transformed into complexed films with copper ions. 19 We have attempted in this study to electrosynthesize PDAN, polyaniline ͑PANi͒, and composite films of DAN and ANi on iron in aqueous acid. The composite films present good adhesion properties and protect iron b...

Electrochemical impedance spectroscopy investigation of chlorinated rubber‐based coatings containing polyaniline as anticorrosion agent

“…Conducting polymers have been extensively studied in recent years due to a great variety of possible applications in several fields, such as energy storage systems [1][2][3], electrocatalysis [4][5][6], electrodialysis membranes [7][8][9][10], sensors [11][12][13], and anticorrosive coatings [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. They exhibit different oxidation states and behave as electronic or mixed conductors [28].…”

Smart Paint for anodic protection of steel

“…Due to their intrinsic properties, oxidized ICP in contact with metals undergo a reduction inducing the formation or preservation of protective oxides, as occur upon the application of an external current [9][10][11][12][13].…”

“…Accordingly, totally or partially oxidized (charged) ICP provide protection to the metal against corrosion until they become totally uncharged (i.e. 100% of reduction) [12,14].…”

Using Conducting Polymers as Active Agents for Marine Antifouling Paints

“…Together with copper, other toxic biocides such as copper thiocyanate, zinc pyrithione, Diuron  (3-(3',4'-dichlorophenyl)-1,1-dimethylurea) and Irgarol  1051 (2-(tert-butylamino)-4-cyclopropylamino)-6-(methylthio)-1,3,5-triazine) are used to increase the efficiency of antifouling coatings 11 . For some years, the materials known as electric conducting polymers have been employed in the manufacture of protective coatings, against corrosion of metals in two forms: doped and undoped [12][13][14][15][16][17] . These polymers, when doped and conducting, are able to protect steel against corrosion by an anodic protection mechanism, owing to the formation of an iron mixed oxide layer of high protection capacity, as well as being able, in the case of a coating fracture, to regenerate the metal oxide layer.…”