On the mechanism of the anodic protection of aluminium alloy AA5182 by emeraldine base coatings: Evidences of a galvanic coupling

Aluminium AA5182 coupons covered by a polyaniline film in the emeraldine base (EB) form showed increasing corrosion potential and decreasing corrosion current as a function of the thickness of the polymer layer. The cathodic reaction was proved not limited by diffusion of species inside the electrolyte solution and oxygen had no effect on the electrochemical behaviour of the coated samples. An EB coating on indium tin oxide conducting layer appeared slightly electroactive in neutral media. The IR spectra of aluminium coated samples, before and after heating in argon atmosphere, confirmed a redox reaction between the polymer film and the metal. This galvanic coupling can explain the good protective behaviour of emeraldine base against corrosion of aluminium.     

Corrosion protection of stainless steel by a new and low-cost organic coating obtained from cashew nutshell liquid

In this work, the corrosion protection of 316L steel was promoted by an electro-synthesized polymer obtained from the technical cashew nutshell liquid (t-CNSL). Spectroscopic techniques confirmed the polymer formation. The polymer was dispersed in the ethyl acetate solvent and used to form coatings on 316L steel substrates. The coated samples were subjected to electrochemical tests in a saline environment. The coated electrode with poly(t-CNSL) polymer was exposed to the corrosive medium for 24 days, and superior corrosion protection was observed compared with the uncoated sample. The open circuit potential measurements showed that the coated sample possessed a more positive corrosion potential when compared with the uncoated substrate. The electrochemical impedance spectroscopy results indicated that the coated electrode's polarization resistance (R_p) recorded ~1.0 MΩ cm² after 24 days of exposure. A decrease in polarization resistance was observed with the exposure time due to the presence of micropores in the t-CNSL coating. The polarization curves exhibited that the coated electrode with poly(t-CNSL) has lower corrosion current density and less negative corrosion potential than the uncoated steel electrode. Therefore, t-CNSL favors the manufacture of thin poly(t-CNSL) coatings for corrosion protection purposes besides being a low-cost material.     

Undoped polyaniline–surfactant complex for corrosion prevention

Due to the strict regulations on the usage of heavy metals as the additives in the coating industries, the search for effective organic corrosion inhibitors in replacement of metal additives has become essential. Electrically conducting polymers have been shown to be effective for corrosion prevention, but the poor solubility of these intractable polymers has been a problem. We have explored a polyaniline–4-dodecylphenol complex (PANi–DDPh) to improve the dissolution, and it has been shown to be an effective organic corrosion inhibitor. With the surfactant, DDPh, PANi could be diluted into the coatings, and the properties of the coatings were affected. An emeraldine base (EB) form of PANi was also found to be oxidized by the hardener. The oxidized form of polyaniline provides improved corrosion protection of metals than that of emeraldine base since the value of the standard electrode potential for the oxidized form of PANi is higher than that of EB. Additionally, the surfactant improves the wet adhesion property between the coating and the metal surface. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2849–2856, 1999     

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.     

Electrochemical synthesis of poly-2-aminothiazole on mild steel and its corrosion inhibition performance

2-Aminothiazole (AT) was polymerized by electrochemical technique on a mild steel (MS) electrode from 0.01 M monomer containing 0.3 M ammonium oxalate solution. Cyclic voltammetry was used for the synthesis. Poly-2-aminothiazole (pAT) film with a light-brownish color was obtained on the MS surface. The effectiveness of polymer film in preventing corrosion of MS was tested in 0.5 M HCl solution. For corrosion tests, anodic polarization curves, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques were utilized. The results obtained indicated that, the polymer film adherent to the steel surface. The polymer film gives a good corrosion protection against the attack of corrosive environment.     

Coatings based on electronic conducting polymers for corrosion protection of metals

In this work, corrosion protection of mild steel by a novel epoxy resin (EP)-based coating system containing polyaniline (PAni) as an anticorrosive agent was studied. The corrosion behavior of mild steel samples coated with an EP/PAni-EB (emeraldine base), EP/PAni-ES (emeraldine salt), EP/SPAN (PAni sulfonated), EP/PAni-fibers, EP/PhoZn (zinc phosphate), EP/ChroZn (zinc chromate) or EP/Charge was investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy measurements were utilized. It was found that the addition of three forms of PAni—undoped, sulfonated and fibers—to the EP resin increased its corrosion protection efficiency.     

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.     

Facile in-situ preparation of polyaniline/graphene nanocomposites using methanesulfonic acid

Polyaniline (PANI)/graphene composites were prepared by the in-situ polymerization of aniline in a 1 M aqueous solution of methanesulfonic acid (MSA) containing graphene, which was prepared separately from graphite powders by simple sonication in MSA. Graphite powders spontaneously exfoliated to form graphene (GPM), which was then quenched with excess water, filtered, and dried to produce powders. The dried graphene powders produced were re-dispersed well in a 1 M MSA aqueous solution, in which the in-situ polymerization of aniline was performed. The resulting PANI/GPM composite had a conducting emeraldine salt (ES) form, and showed good electrical and thermal properties, compared to pure PANI prepared using a 1 M HCl solution. The PANI/GPM composite could be dissolved in a MSA solution and spin-coated in a conducting ES form of PANI. In contrast, the ES form produced from a HCl solution was insoluble in organic solvents and needed to be reduced to convert it to the emeraldine base form to produce a PANI solution. Therefore, the in-situ preparation of PANI/graphene composites using MSA provides a facile means of improving the thermal and electrical properties of PANI and its processability.     

Corrosion behavior of ferritic stainless steel alloyed with different amounts of niobium in hydrochloric acid solution

The corrosion behavior of stainless steel alloys containing corrosion-resistant elements was investigated. Ferritic stainless steel (FSSs) electrodes were synthesized by applying a scan rate of 1 mV s⁻¹. Stainless steels were used unalloyed and alloyed with about 0.5, 1, and 3 wt% elemental Nb. The samples were obtained from casting and forging. The samples were classified into three groups. In the first group, samples were unhomogenized and remained in production condition. In the second and third groups, samples were exposed to homogenization at 1,100 °C for 30 min or 180 min, respectively, and then quenched. The corrosion performance of the FSSs was investigated in 0.3 M HCl acid solution using electrochemical impedance spectroscopy (EIS). Corrosion resistance was calculated using the Stearn–Geary equation. SEM investigations of samples immersed in 0.3 M HCl acid solution for 60 and 360 min were performed. SEM micrographs showed generalized pitting. Consequently, it was determined that niobium has a beneficial effect on the corrosion resistance of FSS since niobium reacts with carbon to form stable carbides.     

Electrochemical preparation and characterization of nickel and zinc-modified poly-2-aminothiazole films on mild steel surface and their corrosion inhibition performance

Poly-2-aminothiazole (pAT) was electrochemically synthesized on a mild steel (MS) specimen from 0.3 M aqueous ammonium oxalate solution containing 0.01 M 2-aminothiazole (2-AT) using cyclic voltammetry technique. The synthesized polymer film was then modified by electrodeposition of 100 μg cm⁻² Ni (MS/pAT–Ni) and Zn (MS/pAT–Zn) on top of the polymer surface. The surface morphologies of the polymer films were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental analysis of the surface films was performed by energy dispersive X-ray spectroscopy (EDX). The effectiveness of the coatings in preventing corrosion of MS in 3.5% NaCl solution was assessed using electrochemical techniques. It was found that the obtained coatings were adherent to the steel surface. The pAT film provided a good corrosion protection against the attack of corrosive environment. Moreover, the modification of pAT film by deposition of Ni and Zn on top of the polymer surface significantly enhances the corrosion protection performance of the polymer film by exhibiting an improved barrier effect against the attack of corrosive environment. The surface morphologies and protection ability of the layers were found to be dependent on the type of deposited metal.     

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.     

Corrosion of mild steel with composite polyaniline coatings using different formulations

The protective abilities of composite coatings based on electrochemically and chemically formed polyaniline powder against the corrosion of mild steel were investigated. A polyaniline powder has been prepared in the form of an emeraldine base and benzoate salt through chemical dedoping and doping. The composite coatings using polyaniline powders, which were obtained through different routes, and base coatings, which were not corrosion-resistant, with different formulations were prepared and applied on mild steel samples. The corrosion was investigated using an electrochemical impedance technique in 3% NaCl, and the atmospheric corrosion was assessed in a humidity chamber. Emeraldine–benzoate salts, which are a chemically synthesized polyaniline, offer the best protection with an optimal polyaniline concentration of approximately 5 wt%. The different corrosion behaviors were assessed relative to the presence of aniline oligomers in the samples after characterization using UV–vis spectrophotometry. Upon comparison between the corrosion behavior in 3% NaCl with commercial primer paint for iron and that with a paint containing 5 wt% PANI, the composite coating has superior anticorrosion characteristics. The mechanism for the protection of mild steel from corrosion through composite polyaniline coatings was also considered.     

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.     

Anti-corrosive properties of poly (2-pyridylamine-co-aniline-co-2,3-xylidine) terpolymer coating on mild steel in different corrosive environments

A soluble terpolymer from 2-pyridylamine (2PA), aniline (AN) and 2,3-xylidine (XY), poly (2PA-co-AN-co-XY) was synthesized by chemical oxidative polymerization using ammonium persulfate as an oxidant in hydrochloride aqueous medium. The two copolymers, poly (AN-co-XY) and poly (2PA-co-AN) were also synthesized by following identical synthesis route. The resultant terpolymer and copolymers were characterized by Fourier transform infrared (FTIR) and ¹H NMR spectroscopy. The terpolymer and copolymers were chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of terpolymer and copolymers coatings 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 measurements, potentiodynamic polarization measurements, and atmospheric exposure test. The corrosion performance of terpolymer and copolymers coatings was also compared separately with polyaniline (PANi) homopolymer coating. The surface morphology of terpolymer and copolymers coatings was evaluated using scanning electron microscopy (SEM). The synthesized terpolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 93–96% after 30 days of immersion. The corrosion performance of individual copolymers was found inferior than the terpolymer. However, the performance of copolymer poly (2AN-co-XY) was found better than copolymer poly (2PA-co-AN).     

Composite multilayered coatings on mild steel

A composite multilayered coating which consisted of an electrodeposited Zn–Fe alloy layer, a zinc phosphate conversion layer, and one, two, or three organic layers was deposited on a mild steel substrate. The adhesion between these multilayered coating and the mild steel substrate was studied with the aid of a scratch testing technique. Observation of the worn surface of different multilayered coatings was performed with the aid of metallurgical microscopy. The same multilayered coatings were examined with FTIR spectroscopy and X-ray diffraction techniques. Finally, the corrosion behavior of bare and multilayered coated mild steel in 0.1 M NaCl solution (pH = 5.5, T = 25°C) was studied.     

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.     

Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Preparation of polyaniline nanofibers and their use as a cathode of aqueous rechargeable batteries

Normal pulse voltammetric method was used to synthesize nanofibers of polyaniline (PANi) in HCl solution on a platinum electrode. The influences of the synthesis parameters, such as potential increment, pulse duration and monomer concentration on the electrochemical properties of the PANi films were investigated. Scanning electron microscopic micrographs clearly revealed the formation a nanofiber structure with average diameter in range 70-100 nm under optimum experimental conditions. The electrochemical properties of PANi films were studied with the impedance analysis, cyclic voltammetry and charge/discharge capacities. FT-IR results revealed that the PANi nanofibers were in emeraldine salt form. The film was employed as a positive electrode (cathode) for a PANi-Zn secondary battery containing 1.0 M ZnCl₂ and 0.5 M NH₄Cl as electrolyte. The cells were charged and discharged under a pulse current of 0.31 mA cm⁻². It was found that the maximum capacity of the PANi-Zn battery is 235.60 Ah kg⁻¹ with a columbic efficiency of 97-100% over a wide range of current density of 0.3-5.6 mA cm⁻². The specific energy was 287.43 Wh kg⁻¹ and the PANi cathode exhibited good recycleability.     

Laterally Controlled Template Electrodeposition of Polyaniline

Polyaniline (PANi) was electrodeposited in gold-coated nanoporous alumina membranes (NAMs) by anodic polymerization of aniline. PANi deposition was followed by cathodic deposition of Ag or Cu, to form a layer of PANi–metal segmented nanowires in the NAM. The compact PANi nanowires fill the entire pore volume, providing a sharp transition from the polymer to the metal segment. The deposited metal layer enables SEM visualization of the PANi nanowire length in the membrane. Deposition of Cu on PANi nanowires occurs at potentials where the PANi is in its reduced leucoemeraldine state, with no evidence for penetration of the metal into the polymer matrix. The mechanism of metal ion reduction on the nonconducting polymer wires is not yet clear. Free-standing segmented PANi–Ag and PANi–Cu nanowires obtained by membrane dissolution show a sharp heterojunction between the polymer and metal phases and are mechanically stable. Aniline electropolymerization in the insulating NAM under a lateral potential gradient generated a thickness gradient of the PANi deposit, revealed by subsequent Cu deposition. The potential-dependent length of the PANi nanowires follows the PANi conductivity pattern, reaching a maximum in the region of stability of the conducting emeraldine phase. The results demonstrate the possibility of obtaining nonlinear graded materials using electrochemical systems showing a complex current–voltage behavior.     

Service life prediction of organic coatings: electrochemical impedance spectroscopy vs actual service life

Electrochemical impedance spectroscopy (EIS) is used to derive an expression for predicting the service life of organic coating in a C4-type environment (industrial and costal areas with moderate salinity) as defined in ISO 12944 standard for paints and varnishes—corrosion protection of steel structures by protective paint systems. Three coating systems with a record of 2, 5, and 10 years of durability were selected for the study. The selection was also based on proven composition and dry film thickness (DFT) of the coatings as per ISO 12944. Electrochemical impedance measurements of the paint-coated panels were carried out by exposing the coated mild steel panels without scribe in different corrosive environments such as immersion in NaCl solution, neutral salt spray, etc. Neutral salt spray exposure was found to be the most severe corrosive environment among all the three coating systems. In most of the cases, EIS gave early indication of coating failure when compared to visual defects such as blistering and over-film corrosion.