Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.     

Electrosynthesis of PAni/PPy coatings doped by phosphotungstate on mild steel and their corrosion resistances

Polyaniline/polypyrrole (PAni/PPy), polyaniline-phosphotungstate/polypyrrole (PAni-PW₁₂/PPy) and PAni/PPy-PW₁₂ have been successfully electrodeposited on mild steel (MS) by cyclic voltammetry in aqueous oxalic acid solutions. It was found that the incorporation of PW₁₂ enhanced the corrosion resistance of PAni/PPy coating. Moreover, in comparison to PAni-PW₁₂/PPy, PAni/PPy-PW₁₂ coating exhibited better corrosion resistance for mild steel. After immersion of 36 h in 0.1 M HCl, for instance, the polarization resistance of PAni/PPy-PW₁₂ coating reached 1695 Ω cm², more than those of both PAni/PPy and PAni-PW₁₂/PPy.     

Comparison of the corrosion protection of mild steel by polypyrrole–phosphate and polypyrrole–tungstenate coatings

The electrodeposition of polypyrrole–phosphate (PPy–P) and polypyrrole–tungstenate (PPy–W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy–P and PPy–W films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) and tungstenate (PPy–W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open‐circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–W coatings could provide much better protection than the PPy–P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X‐ray analyses. The results reveal that the PPy–P and PPy–W coated electrodes offered a noticeable enhancement in protection against corrosion processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Molybdate‐doped copolymer coatings for corrosion prevention of stainless steel

The polypyrrole and polyaniline copolymer coating (PPy‐PAni) and PPy‐PAni doped with sodium molybdate copolymer coating ( ) were synthesized on stainless steel by cyclic voltammetry. The effect of molybdate on the passivation of stainless steel was investigated by linear sweep voltammetry in 0.2 mol L^?1 of oxalic acid. The corrosion prevention performances of these copolymer coatings for stainless steel were investigated by linear sweep voltammetry, electrochemical impedance spectroscopy in 1 mol L^?1 of sulfuric acid, and potentiodynamic polarization in 0.1 mol L^?1 of hydrochloric acid. Copolymer coating doped with molybdate could accelerate the formation of the passive oxide film and have better corrosion prevention efficiencies than PPy‐PAni coating on stainless steel. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40602.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Corrosion protection of mild steel by polypyrrole phosphate composite coating

Electrodeposition of polypyrrole phosphate (PPy–P) on mild steel (ST₁₂) was achieved in oxalic acid medium using cyclic voltammetry (CV) technique. Adherent and homogeneous PPy–P films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) coatings in 3.5% NaCl solutions was investigated through potentiodynamic polarization technique, open circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). Based on a physical model for the corrosion of mild steel composite, the Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–P coatings could provide much better protection than PPy. The effect of phosphate on the morphology and structure of the passive film was investigated by scanning electron microscopy and electron dispersion X-ray analysis (EDX). The results reveal that the PPy–P coated electrode provided a noticeable enhancement of protection against corrosion process.     

Electrochemical synthesis of bilayer coatings of poly(N-methylaniline) and polypyrrole on mild steel and their corrosion protection performances

Homopolymer and bilayer coatings of poly(N-methylaniline) (PNMA) and polypyrrole-dodecylsulfate (PPy-DS) have been electropolymerized on a mild steel (MS) surface by the potentiodynamic method in aqueous oxalic acid solutions. In order to include dodecylsulfate ion as dopant in the polypyrrole, sodium dodecylsulfate was also added to the polymerization solution of pyrrole. Characterization of coatings was carried out by the cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). Corrosion behavior of the polymer coated MS electrodes was investigated in highly aggressive 0.5 M HCl solution by the Tafel test and electrochemical impedance spectroscopy (EIS) techniques. Corrosion test revealed that among the protective coatings obtained, the PNMA/PPy-DS bilayer exhibited the best corrosion resistance at all immersion times.     

The electrochemical copolymerization of pyrrole and bithiophene on stainless steel in the presence of SDS in aqueous medium and its anticorrosive performance

For the first time, the electrosynthesis of poly(pyrrole-co-bithiophene) copolymers (P(Py-co-BT) I, II, III) was carried out using the potentiostatic technique on stainless steel (SS) electrode from aqueous oxalic acid solutions containing fixed concentration of bithiophene (BT) and different concentrations of pyrrole (Py) in the presence of sodium dodecylsulfate (SDS). Corrosion protection behaviors of these copolymer-coated steels were investigated in 3.5% NaCl solution by potentiodynamic polarization, Tafel test technique and electrochemical impedance spectroscopy (EIS). Among the protective copolymer coatings, the P(Py-co-BT) II, which was obtained from polymerization solution containing 0.025 M Py, exhibited the best protection against corrosion. Hence, only this copolymer was characterized by cyclic voltammetry, FT-IR, UV–vis, conductivity measurement and differential scanning calorimetry (DSC) by comparing with those of the polybithiophene (PBT) and polypyrrole (PPy) homopolymers. It was determined that this polymer was the polypyrrole-based copolymer. The incorporation of BT units into PPy chains not only increased dry conductivity but also developed the toughness of polymer.     

Mica/polypyrrole (doped) composite containing coatings for the corrosion protection of cold rolled steel

Micas/polypyrroles (PPys) doped with molybdate, p-toluene sulfonate, dodecyl benzene sulfonate, and 2-naphthalene sulfonate composite pigments were synthesized by chemical oxidative polymerization and characterized in coatings for corrosion protection on cold rolled steel substrate by various electrochemical techniques. Synthesized composite pigments were characterized for morphology by scanning electron microscopy, which indicated physical formation of PPy on the surface of mica. Chemical composition of the composite pigments was analyzed by X-ray photoelectron spectroscopy which chemically confirmed doped PPy formation on the mica surface. Coatings were formulated at 20% pigment volume concentration (composite pigments or as-received mica pigment) and were applied on cold rolled steel substrate. Coatings were exposed to salt spray test conditions (ASTM B117) for 30 days and were periodically assessed for corrosion with electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and potentiodynamic polarization. EIS and circuit modeling results demonstrated higher coating resistance (R _c) for mica/PPy (doped) composite coatings as compared to as-received mica pigment containing coating after 30 days of salt spray exposure. Lower current density and more positive corrosion potential values were observed for mica/PPy (doped) composite coatings as compared to mica pigment-based coating in potentiodynamic polarization measurements, indicating improved corrosion protection for cold rolled steel substrate. OCP measurements revealed more positive values for mica/PPy (doped) composite coatings as compared to mica pigment-based coating suggesting superior corrosion protection for mica/PPy (doped) composites.     

Electropolymerization of poly(N-ethyl aniline) on mild steel: Synthesis, characterization and corrosion protection

Poly(N-ethylaniline) (PNEA) coatings on the mild steel electrode were synthesized by electrochemical oxidation of N-ethylaniline using aqueous oxalic acid solutions as reaction medium. Electrodeposition was carried out by potentiodynamic, potentiostatic and galvanostatic synthesis techniques. Smooth, adhesive and thick PNEA coatings on mild steel could be electrosynthesized during sequential scanning of the potential region between −0.5 and 1.4 V versus SCE, with scan rate of 20 mV s⁻¹. The electrodeposited coatings were characterized by cyclic voltammetry, FT-IR and UV-vis techniques. Corrosion behavior of PNEA coated steels was investigated by linear anodic potentiodynamic polarization technique and Tafel test. Anodic potentiodynamic polarization results showed that electrodissolution current value of PNEA coated steel decreased about 90% compared to that of the uncoated steel in 0.5 M H₂SO₄ aqueous solution. Tafel plots showed also strong decrease of corrosion current for the PNEA coated electrode compared to the uncoated steel electrode in 3% NaCl as corrosive medium.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Zinc deposited polymer coatings for copper protection

Polypyrrole (PPy) and polyaniline (PAni) coatings were electrosynthesized on copper, by using cyclic voltammetry technique. Then, these coatings were modified with the deposition of zinc particles from aqueous zinc sulphate solution. The electrodeposition of zinc was achieved at a constant potential value of −1.20 V, in the amount of ∼0.75 mg/cm². The corrosion performance of zinc modified polymer coatings were investigated in 3.5% NaCl solution; by using the electrochemical impedance spectroscopy (EIS), and anodic polarization curves. The zinc particles improved the barrier property of polymer films, thanks to formation of voluminous zinc corrosion products within the pores of polymer coating. Also, the zinc particles provided cathodic protection to the substrate, where the polymer film played the role of conductance between zinc particles and copper.     

Corrosion‐protection aspects of electrochemically synthesized poly(o‐anisidine) coatings on mild steel: An electrochemical impedance spectroscopy study

The corrosion‐protection aspects of poly(o‐anisidine) (POA) coatings on mild steel in aqueous 3% NaCl solutions were investigated with electrochemical impedance spectroscopy, a potentiodynamic polarization technique, and open circuit potential measurements. The POA coatings were electrochemically synthesized on mild steel with cyclic voltammetry from an aqueous salicylate medium. The corrosion behavior of the POA coatings was investigated through immersion tests performed in aqueous 3% NaCl solutions, and the recorded electrochemical impedance spectra were fitted with an equivalent circuit to obtain the characteristic impedance parameters. The use of a single equivalent circuit was inadequate to explain the various physical and electrochemical processes occurring at different exposure times. It was suggested that some characteristic element(s) should be incorporated into the equivalent circuit at different stages of the immersion to elucidate the various processes occurring at different exposure times. The evolution of the impedance parameters with the immersion time was studied, and the results showed that POA acted as a protective coating on the mild steel against corrosion in a 3% NaCl solution. From these data, the water uptake and delamination area were determined to further support the corrosion‐protection performance of the POA coating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electropolymerized bilayer coatings of polyaniline and poly(N-methylaniline) on mild steel and their corrosion protection performance

Polyaniline (PANI) and poly(N-methylaniline) (PNMA) have been electrodeposited on mild steel from oxalic acid bath using cyclic voltammetric technique. Pretreatments like passivation and primer polymer coatings were required for effective coating. Differently stacked composite polymer layers on the metal surface by layer-by-layer approach have also been obtained and their properties have been compared with their corresponding copolymer coatings. FTIR study confirms the formation of electroactive polymer compounds on mild steel. Evaluation of these coatings in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy reveals significant corrosion resistant behavior. Relatively higher corrosion protection is exhibited by copolymer coatings and composite-bilayer coatings than the corresponding homopolymer coatings. The composite metal–PANI–PNMA layer shows higher stability and better protection than the metal–PNMA–PANI layer.     

Synthesis and corrosion protection aspects of poly(<Emphasis Type="Italic">o</Emphasis>-toluidine)/CdO nanoparticle composite coatings on mild steel

This study examines the possibility of using poly(o-toluidine)/CdO (POT-CdO) nanoparticle composite coating for corrosion protection of mild steel in chloride environment. The POT-CdO nanoparticle composite coating was synthesized on mild steel from aqueous tartrate solution containing CdO-nanoparticles (size ~18 nm) by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, UV–Visible absorption spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction measurements. The corrosion protection aspects of the resulting POT-CdO nanocomposite structure were investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy. The results of these investigations reveal that the POT-CdO nanoparticle composite acts as a protective coating on mild steel and reduces the corrosion rate of mild steel almost by factor of 70.     

Electrochemical synthesis of poly(N-methylaniline) on an iron electrode and its corrosion performance

Synthesis of poly(N-methylaniline) (PNMA) on pure iron and Pt electrodes was carried out from aqueous 0.3 M oxalic acid solution containing 0.1 M N-methylaniline (NMA) by potentiodynamic and galvanostatic techniques. It was found that when compared to polyaniline (PAni) and its ring- and N-ethyl-substituted derivatives, PNMA can be electrosynthesized with lower upper scanning potential (upper potential limit, E_upp) of 0.8 V vs. saturated calomel electrode (SCE) on an Fe electrode. PNMA coatings were characterized by electrochemical, scanning electron microscopy (SEM) and FTIR techniques. Linear anodic potentiodynamic polarization results proved that increasing the acidity of the polymerization solution causes more effective protection against corrosion in 0.5 M H₂SO₄ medium for PNMA. Moreover, PNMA exhibited similar protective properties with PAni under the same corrosion test conditions. Tafel test results reveal that the PNMA coating appears to enhance protection for iron in 0.5 M NaCl and 0.1 M HCl solutions. According to EIS results, the PNMA coating is able to offer protection to Fe electrodes in NaCl compared to that in HCl medium over a long immersion period.     

Effect of the polymer layers and bilayers on the corrosion behaviour of mild steel: Comparison with polymers containing Zn microparticles

Electrodeposition methods have been used to obtain polypyrrole and polyaniline polymer layers, bilayers and blends of these polymers on carbon steel by passivation of the steel surface in the electrodeposition solution (oxalic acid and monomer) between −0.5 and 0.3 V versus Ag/AgCl and subsequent electrodeposition using different techniques (potentiodynamic, galvanostatic and potentiostatic). The results obtained indicate that prepassivation gives rise to adherent polymer layers with excellent corrosion resistance. Of all the bilayers obtained, the best results are yielded with those in which polyaniline is deposited as the base for the deposition of polypyrrole.

The electrodeposition of Zn microparticles on the previously deposited polymer layers promotes a great improvement in the corrosion current in highly aggressive solutions such as NaCl due to the effect of Zn as an anodic corrosion inhibitor. The drop in the corrosion rate depends on the amount of Zn deposited on the polymer layer, up to a certain point after which the protective effect ceases to be observed.     

Corrosion performance of chemically synthesized poly(aniline-co-o-toluidine) copolymer coating on mild steel

A soluble copolymer from aniline and o-toluidine [poly(aniline-co-o-toluidine)] was synthesized by chemical oxidative copolymerization using ammonium persulphate as an oxidant in hydrochloride aqueous medium. The resultant copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy and chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of copolymer coating was investigated in major corrosive environments, such as 0.1 M HCl, 5% NaCl solution, artificial seawater, distilled water and open atmosphere by conducting various corrosion tests which include: immersion test, open circuit potential (OCP) measurements, potentiodynamic polarization measurements and atmospheric exposure test. The corrosion performance of copolymer coating was also compared separately with polyaniline (PANi) and poly(o-toluidine) (POT) homopolymer coatings. The surface morphologies of polymer coatings were evaluated using scanning electron microscopy (SEM). The synthesized copolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 78–94% after 30 days of immersion. The corrosion performance of copolymer in 5% NaCl and artificial seawater was comparable, which was only marginally better than in 0.1 M HCl. In general, the performance of copolymer coating was found to be better than that of homopolymer coatings.     

PAni/SBR composite as anticorrosive coating for carbon steel,part II: electrochemical characterization

Conducting polymer composites have gained popularity into the field of organic anticorrosive coatings research due to their low environmental and health impact. In this work, the effect of the conducting polymer/elastomer ratio and the PAni doping method on the electrochemical behavior of polyaniline/styrene butadiene rubber films (PAni/SBR) has been studied in order to evaluate the performance of the proposed coatings for carbon steel corrosion prevention. According to open circuit potential measurements, linear polarization resistance tests, electrochemical impedance spectroscopy and polarization curves, the use of dodecyl benzene sulfonic acid as doping agent and the reduction of the PAni content in the composite enhance the anticorrosive behavior of PAni/SBR composites by inducing carbon steel passivation process.     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.