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.     

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.     

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 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.     

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.     

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.     

Electropolymerization, characterization and corrosion performance of poly(N-ethylaniline) on copper

Poly(N-ethylaniline) (PNEA) coatings were grown by cyclic voltammetry technique on copper from 0.1 M N-ethylaniline (NEA) in 0.3 M oxalic acid solution. The optimum conditions (e.g. upper potential limit, scan rate and cycle number) effect on corrosion performance of synthesized PNEA films were determined in order to obtain best protection results against corrosion. The electrodeposited coatings were characterized by cyclic voltammetry (CV), Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) spectroscopy and scanning electron microscopy (SEM). Redox parameters were found after electrochemical tests and results of stability tests of these films impart an electroactive behavior that is composed of both diffusion control and thin film behavior. In addition, corrosion performance of PNEA coatings were investigated in 0.1 M H₂SO₄ by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) techniques.     

Influence of chloride ion concentration on the electrochemical corrosion behaviour of plasma electrolytic oxidation coated AM50 magnesium alloy

The electrochemical degradation of a silicate- and a phosphate-based plasma electrolytic oxidation (PEO) coated AM50 magnesium alloy obtained using a pulsed DC power supply was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in NaCl solutions of different chloride ion concentrations viz., 0.01 M, 0.1 M, 0.5 M and 1 M. The surface of the PEO coated specimens after 50 h of immersion/EIS testing was examined by optical microscopy and scanning electron microscopy. The results showed that the corrosion deterioration of PEO coated magnesium alloy in NaCl solutions was significantly influenced by chloride ion concentration. The silicate-based coating was found to offer a superior corrosion resistance to the magnesium substrate than the phosphate-based coatings in lower chloride ion concentration NaCl solutions (0.01 M and 0.1 M NaCl). On the other hand both these PEO coatings were found to be highly susceptible to localized damage, and could not provide an effective corrosion protection to Mg alloy substrate in solutions containing higher chloride concentrations (0.5 M and 1 M). The extent of localized damage was observed to be more with increase in chloride concentration in both the cases.     

Inhibition of copper corrosion in acidic pickling solutions by N-phenyl-1,4-phenylenediamine

Inhibition of copper corrosion by N-phenyl-1,4-phenylenediamine (NPPD) has been investigated in de-aerated, aerated, and oxygenated aqueous 0.50 M HCl solutions by using potentiodynamic polarization, potentiostatic current-time, electrochemical impedance spectroscopy, and weight-loss measurements, along with scanning electron microscopic (SEM) and energy dispersive X-ray (EDX) experiments. Potentiodynamic polarization measurements showed that the NPPD molecules significantly decrease cathodic, anodic, and corrosion currents in all these solutions. Potentiostatic current-time measurements as well as SEM and EDX investigations of the copper surface revealed that NPPD suppresses the copper dissolution current due to its adsorption on the copper surface as a Cu(I)-NPPD complex. Impedance measurements also supported the results obtained from both the potentiodynamic and potentiostatic experiments. The inhibition efficiencies measured from polarization, electrochemical impedance spectroscopy (EIS), and weight-loss experiments are all internally consistent with each other. These results together showed that NPPD is a good mixed-type inhibitor for copper corrosion in all solutions studied.     

Synthesis and characterization of poly(aniline) and poly(o-anisidine) films in sulphamic acid solution and their anticorrosion properties

Poly(o-anisidine) (POA) and polyaniline (PANI) coatings were synthesized on platinum (Pt) surface and stainless steel (SS) in monomer containing 0.50 M sulphamic acid (SA) solution by means of cyclic voltammetry (CV) technique. Meanwhile, poly(o-anisidine) film was also deposited with a different scan rate on SS electrode. The behaviour of PANI and POA films obtained on stainless steel examined by CV was different from the one obtained for PANI and POA on Pt electrode. The corrosion performances of PANI and POA coatings in 3.5% NaCl solution were investigated with anodic polarization technique and electrochemical impedance spectroscopy (EIS). EIS measurements verified the effect of monomers and that of scan rate on corrosion inhibition of coatings on SS electrode. The results showed that POA film synthesized at low scan rate exhibited an effective anticorrosive property on SS electrode. POA synthesized at low scan rate and PANI coatings provided a remarkable anodic protection to SS substrate for longer exposure time than the one observed for POA coating produced at high scan rate as well as that of bare SS electrode.     

Corrosion protective poly(o-ethoxyaniline) coatings on copper

Poly(o-ethoxyaniline) (POEA) coatings were synthesized on copper (Cu) by electrochemical polymerization of o-ethoxyaniline in aqueous salicylate solution by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The performance of POEA as protective coating against corrosion of Cu in aqueous 3% NaCl was assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization and EIS studies demonstrate that the POEA coating has ability to protect the Cu against corrosion. The corrosion potential was about 0.330 V versus SCE more positive in aqueous 3% NaCl for the POEA coated Cu than that of uncoated Cu and reduces the corrosion rate of Cu almost by a factor of 140.     

Ortho-substituted anilines to inhibit copper corrosion in aerated 0.5 M hydrochloric acid

Aniline derivatives, namely 2-chloroaniline, 2-fluoroaniline, 2-aminophenetole, 2-ethylaniline, o-aminoanisole and o-toluidine were studied for their possible use as copper corrosion inhibitors in 0.5 M HCl. These compounds were studied in concentrations from 10⁻³ to 10⁻⁴ M at temperature 298 K. Effectiveness of these compounds was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. These compounds inhibit the corrosion of copper in HCl solution to some extent. In each case, inhibition efficiencies increase with increasing concentration. A suggested model for the interface as well as some kinetic data is presented. These inhibitors obey the Temkin adsorption isotherm. A correlation between structure and inhibition efficiencies is suggested.     

Corrosion inhibition of stainless steel by polyaniline,poly(2-chloroaniline), and poly(aniline-co-2-chloroaniline) in HCl

Polyaniline (PANi), poly(2-chloroaniline) (PClANi), and poly(aniline-co-2-chloroaniline) (co-PClANi) films were synthesized by electrochemical deposition on 304-stainless steel (SS) from an acetonitrile solution. The structural properties of these polymer films were characterized by spectroscopic (FTIR and UV–vis) and electrochemical (cyclic voltammetry) methods. Open circuit potential–time (E_ocp–time) curves, potentiodynamic polarization, and electrochemical impedance (EIS) measurements showed that these films have significant protective performance against corrosion of SS in 0.5 M HCl solution. It was found that co-PClANi film has acted as a passivator as well as barrier for cathodic reduction reaction in a similar manner as PANi film. However, PClANi film has behaved only as barrier for corrosion protection of SS in 0.5 M HCl.     

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.     

Poly(N-methylpyrrole) electrodeposited on copper: Corrosion protection properties

Electrochemical synthesis of poly(N-methylpyrrole) films on copper electrodes from an aqueous oxalic acid has been achieved. A potential higher than 2 V (SCE) was needed to generate the polymer, for this reason, the polymer was in the overoxidized state. The inhibiting corrosion properties of this coating on copper were investigated for the first time in aqueous 0.1 M sodium chloride solution using potentiodynamic polarization, Tafel analyses, open-circuit potential and electrochemical impedance spectroscopy. Corrosion protection properties comparable to those of polypyrrole (PPy) films were observed for these films. A physical barrier effect is the most likely protection mechanism.     

Styrene butadiene co-polymer based conducting polymer composite as an effective corrosion protective coating

Electroactive conducting polymer composite coatings of polyaniline (PANI) are electrosynthesized on styrene–butadiene rubber (SBR) coated stainless steel electrode by potentiostatic method using aqueous H₂SO₄ as supporting electrolyte. The protective behaviour of these coatings in different corrosion media (3.5% NaCl and 0.5 M HCl) is investigated using Tafel polarization curves, open circuit potential measurements and electrochemical impedance spectroscopy. The results reveal that SBR/PANI composite coating is much better in corrosion protection than simple PANI coating. The corrosion potential of composite films shifts to more noble values indicating that SBR/PANI composite coating act as an effective corrosion protective layer.     

Effect of ethylenediamine tetraacetic acid disodium on the corrosion of cold rolled steel in the presence of benzotriazole in hydrochloric acid

The inhibition behavior of cold rolled steel in 0.1 M hydrochloric acid (HCl) by ethylenediamine tetraacetic acid disodium (EDTA) in the absence and presence of benzotriazole (BTA) was investigated with Tafel polarization curve and electrochemical impedance spectroscopy (EIS). The polarization curve results show that the single EDTA acts as an anodic type inhibitor while the combination of EDTA and BTA acts as mixed type inhibitor and mainly inhibits anodic reaction. All impedance spectra in EIS tests exhibit one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. Inhibition efficiencies obtained from Tafel polarization, charge transfer resistance (R_t) are consistent. The corrosion of cold rolled steel in 0.1 M HCl is obviously reduced by EDTA in combination with lower concentrations of BTA. Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used to characterize the corrosion surface of cold rolled steel. Probable mechanisms are present to explain the experimental results.     

Acceleration and quantitative evaluation of degradation for corrosion protective coatings on buried pipeline: Part I. Development of electrochemical test methods

The electrochemical degradation of polyethylene coated onto SS400 was examined in synthetic groundwater. Electrochemical techniques (electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization tests) and surface analysis (scanning electron microscopy) were used to accelerate and evaluate the coating degradation. The pulsed potentiostatic polarization test accelerating both the cathodic reduction and anodic oxidation reactions was applied to reproduce the coating degradation mechanisms of cathodic disbondment and oxide lifting. The applied potentials were determined to be ±300 mV_SCE versus open-circuit potential from the analysis of the anodic and cathodic polarization data. Results from the EIS confirmed that coating degradation is accelerated effectively by the pulsed potentiostatic polarization testing.     

Electrochemical impedance spectroscopy and corrosion behaviour of Al2O3-Ni nano composite coatings

In this paper, the results on the electrochemical impedance spectroscopy and corrosion properties of electrodeposited nanostructured Al₂O₃-Ni composite coatings are presented. The nanocomposite coatings were obtained by codeposition of alumina nanoparticles (13 nm) with nickel during plating process. The coating thickness was 50 μm on steel support and an average of nano Al₂O₃ particles inside of coatings at 15 vol.% was present. The structure of the coatings was investigated by scanning electron microscopy (SEM). It has been found that the codeposition of Al₂O₃ particles with nickel disturbs the nickel coating's regular surface structure. The electrochemical behavior of the coatings in the corrosive solutions was investigated by polarization potentiodynamic and electrochemical impedance spectroscopy methods. As electrochemical test solutions 0.5 M sodium chloride and 0.5 M potassium sulphate were used in a three electrode open cell. The corrosion potential is shifted to more negative values for nanostructured coatings in 0.5 M sodium chloride. The polarization resistance in 0.5 M sodium chloride decreases in 24 h, but after that increases slowly. In 0.5 M potassium sulphate solution the polarization resistance decreases after 2 h and after 30 h of immersion the polarization resistance is higher than that of the beginning value. The corrosion rate calculated by polarization potentiodynamic curves obtained after 30 min from immersion in solution is smaller for nanostructured coatings in 0.5 M potassium sulphate (4.74 μm/year) and a little bit bigger in 0.5 M sodium chloride (5.03 μm/year).     

Effects of nitrogen on the passivation of nickel-free high nitrogen and manganese stainless steels in acidic chloride solutions

The role of nitrogen on the passivation of nickel-free high nitrogen and manganese stainless steels was investigated in 0.5 M H₂SO₄, 3.5% NaCl and 0.5 M H₂SO₄ + 0.5 M NaCl solutions using potentiodynamic polarization, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy techniques. The passive film stability was enhanced in 0.5 M H₂SO₄ and the pitting resistance was improved in 3.5% NaCl solution by more nitrogen addition. The influence of nitrogen extended the whole anodic polarization region in 0.5 M H₂SO₄ + 0.5 M NaCl solution, as demonstrated by the enhanced dissolution resistance, promoted adsorption and passivation process, improved film protection and pitting resistance with increasing nitrogen content. Possible mechanisms relating to the role of nitrogen in different potential regions were discussed.