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Application of polyaniline/nylon composites coating for corrosion protection of steel

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Abstract

In this research, we investigated the corrosion inhibition properties of polished steel plates (low carbon) coated with a polyaniline (emeraldine base form) blend with nylon 66 (termed PANi/Ny) via cast method with formic acid as the solvent. Polyaniline (PANi) was prepared chemically from aqueous solution using aniline (0.2M) as a monomer and ammonium persulfate (0.2M) as an oxidant. The polymer powder produced was changed into emeraldine base (EB) form after treatment with dilute ammonia solution (0.5M) in order to do further processing. The corrosion experiments were performed in the open circuit, exposing samples to different aggressive and corrosive conditions (e.g., NaCl, HCl). To produce a good comparison, the corrosion study was performed on both polymer-coated and bare-steel samples. Corrosion monitoring was performed by simple immersion tests and determination of the concentration of iron ions and metal weight loss in test solutions. It was found that PANi/Ny coatings can provide an anodic protection against corrosive environments in which the metals are exposed. The corrosion rate for the polymer coated steel was significantly lower than the bare steel (~10–15 times).

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Bismaleimide (BMI) coating with and without aluminum oxide (Al2O3), silica oxide (SiO2), hexagonal boron nitride (h-BN), or organophilic montmorillonite clay 30B (OMMT) fillers on 1018 steel substrates was studied. Bilayer coatings consisting of BMI with one of the fillers at 5 wt.% for the first layer and pure BMI for the second layer were applied on 1018 steel substrates. The corrosion resistance of all coated samples was investigated through potentiodynamic polarization by using Tafel method in 4.2 wt.% sea salt solution. The results of the test showed that pure BMI coating improved the corrosion resistance by reducing the corrosion rate by 88%. Addition of 5 wt.% of OMMT or SiO2 fillers increased the efficiency of the coating in reducing corrosion rate by 99 and 97%, respectively. Adding 5 wt.% h-BN showed marginal improvements in the reduction in corrosion rates (89%). Addition of 5 wt.% Al2O3 as a filler dropped the efficiency of BMI coating to 64%. Adhesion of the coated steel was also affected depending on the filler type. Micro-hardness measurements using Vickers scale were taken to assess coating hardness, and scanning electron microscopy was used to investigate the dispersion of filler particles in the matrix.
Article
Kaolinite/polyaniline nanocomposites (KPAns) were prepared by in situ chemical oxidative polymerization. The nanocomposites were synthesized with four different aniline to kaolinite weight percentage; 5, 10, 15, and 20% to produce KPAn5, KPAn10, KPAn15, and KPAn20, respectively. The structural, morphological and thermal properties of the nanocomposites were characterized using Fourier transform infrared, X‐ray diffraction, scanning electron microscope (SEM)–energy dispersive X‐ray analyzer, transmission electron microscope, and Thermogravimetric analysis. The results revealed a very slight increase in the d‐spacing of kaolinite XRD peaks. SEM images showed hexagonal platy sheets of kaolinite crystals that are indistinguishable in KPAn nanocomposites images, especially on using a high amount of polyaniline (PANI). The increase in the percentage of carbon and nitrogen elements in EDAX data proved the adsorption of PANI on the surface of kaolinite platelets. To investigate the anticorrosive performance of the synthesized nanocomposites, kaolinite and KPAn nanocomposites were loaded in various amounts (1, 5, and 9%) in a blend of chlorinated rubber/medium oil alkyd resin (CR/MA) to prepare different formulations that were applied and evaluated as protective coats on steel substrates. Visual corrosion test revealed that 5% KPAn‐loaded CR/MA coats exhibited the best protection against corrosion amongst other formulations as indicated by their lowest degree of rusting and blistering. Potentiodynamic polarization measurements confirmed the highest protection of 5% KPAn10‐loaded CR/MA coat as indicated by the quantitative corrosion rates obtained from Tafel extrapolation. POLYM. COMPOS., 2018.
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Conducting polyaniline (PANI)/cadmium sulfide (CdS) nanocomposite films were prepared by in situ chemical oxidation method. The prepared nanocomposites were characterized by fourier transform infra‐red spectroscopy, X‐ray diffraction, and scanning electron microscopy for structural and morphological analysis. The effect of CdS content on structural and morphological features of PANI matrix are discussed in detail. The frequency dependent room temperature conductivity and dielectric properties of these composites were studied by measuring various parameters in the frequency range 10–106 Hz. The role of surface modification on electrical and dielectric properties of the composites was analyzed and it was found that, the concentration of CdS in PANI matrix has a greater influence on electrical properties due to the alteration of molecular chains in PANI matrix. Among various nanocomposites so prepared, the composite with 3 wt% of CdS in PANI matrix (P3) shows better conductivity and dielectric behavior which could be of great importance in various technological applications. The possibility of these materials being used as transistors, energy storage and nano dielectric devices could be explored further. POLYM. COMPOS., 2018.
Article
The corrosion behavior of mild steel and AISI 304L SS in the presence of dissolved Zn ions under different experimental conditions have been investigated. Experimental conditions include: variation in aqueous medium, Zn ions concentration, pH, dissolved oxygen, and flow condition. The variation in corrosion rate in the presence of varying concentrations of Zn ions was determined using weight loss technique and spectrophotometric analysis of iron ions entered into the test solutions after completion of immersion. The pH of the test solutions was also monitored during the entire period of immersion. The Zn ions present in the test solutions after completion of immersion were estimated using atomic absorption spectrophotometer (AAS). Open circuit potential (OCP) measurements and potentiodynamic polarization (PDP) measurements were carried out to find out the role of Zn ions on the corrosion behavior of mild steel and SS 304L. The surface morphology of steel before and after immersion in aqueous solution containing Zn ions was also examined using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The influence of Zn ions on the corrosion behavior of mild steel is quite pronounced and show interesting trends whereas SS 304L is unaffected both in distilled water or artificial seawater.
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Developing efficient multifunctional electrode materials is highly effective to dramatically reduce the overall cost of the electrochemical devices. In this work, we for the first time demonstrate a facile strategy for preparing Prussian blue analogous@polyaniline core–shell nanocubes (denoted as PBAs@PANI) as multifunctional electrode materials for lithium storage and overall water splitting. By finely controlling the reaction parameters, PANI was uniformly coated on the surface of PBAs nanocubes and that the thickness of the PANI shell can be adjusted. The as-synthesized PBAs@PANI nanocubes yield improved electrochemical performance due to significantly enhanced charge transport, elastic buffer, and corrosion protection afforded by the PANI coating. More specifically, PBAs@PANI nanocubes show excellent lithium storage behavior with a reversible capacity of 626 mA h g⁻¹ compared with the uncoated PBAs (203 mA h g⁻¹) after 500 cycles at a high current density of 1 A g⁻¹. Furthermore, PBAs@PANI nanocubes can also efficiently catalyze the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and we therefore investigated their applications as bifunctional electrocatalysts (as both the anode and cathode) for overall water splitting. A current density of 10 mA cm⁻² can be gained at a low cell voltage of 1.73 V over a long-term operation in base, representing a combined overpotential of 500 mV for full water splitting. These superior performances manifest that PBAs@PANI nanocubes can serve as high-performance anode for LIBs as well as promising bifunctional electrocatalysts for overall water splitting.
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Silver nano-particle embedded polyvinylidene fluoride (PVDF) and poly (vinylidene fluoride– hexafluoropropylene) (PVDF-HFP) was prepared by in-situ chemical reaction. The formation of silver nanoparticles was confirmed by UV–vis spectroscopy and HR-TEM image analysis. The weight percentage of silver nano-particle were estimated by thermogravimetric analysis (TGA). Nonisothermal melt-crystallization kinetics and nucleation of molten polymers was analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Different parameters coming from the DSC data recommended that silver nano-particle enhanced the molecular chain mobility of molten PVDF during its crystallization but for PVDF-HFP it hindered the chain mobility. The values of effective activation energies, calculated by the differential isoconventional method supported the results. Fourier transform infrared spectroscopy (FT-IR) and melting thermograms of different samples concluded that silver nano-particles helps to form polar β- phase of molten PVDF during crystallization but it is ineffective for PVDF-HFP.
Article
We report a simple approach for the preparation of superhydrophobic polyaniline (PANI) and its application for the corrosion protection coatings. First, PANI was synthesized conventionally by oxidative polymerization with APS. Subsequently, PANI with different wettability was obtained by modification with different surfactants. The surface modification of PANI with three different surfactants (sodium dodecylbenzenesulfonate, polyethylene glycol, and cetyltrimethylammonium bromide) provided excellent surface superhydrophobicity (water contact angle >150°). The structure and morphology of as-prepared PANI were characterized with Fourier transform infrared, Energy dispersive X-ray spectroscopy, and Scanning electron microscopy. Corrosion protection performance of PANI with different wettability was evaluated in 3.5% NaCl electrolyte using Tafel polarization curves and electrochemical impedance spectroscopy. The results indicated that various superhydrophobic PANI coatings have better anticorrosion performance as compared to the hydrophilic PANI. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44248.
Article
The purpose of this work was to study the treatment of polyaniline wastewater by adsorption of activated carbon and neutralization of calcium carbonate. The polyaniline wastewater generated in the synthesis process contained toxic aniline and its derivatives, which would pollute water and pose severe harm for human health and environment. Activated carbon is a strong adsorbent that could adsorb aniline and its derivatives effectively. Batch experiments such as the concentration of the polyaniline wastewater, adsorbent dose, contact time and pH were carried out to investigate the optimal treatment conditions. Results showed that the optimum conditions were at dilution concentration of 0.08 times of the raw concentration, 16.0 g L-1 activated carbon, 0.5 h and the original pH 1.05. About 91 % organics removal percentage could be reached by this method. Chemical oxygen demand (COD) of the polyaniline wastewater before and after treatment is 838 and 75 mg L-1, respectively and the removal efficiency was more than 91 %. The polyaniline wastewater after adsorption treatment was neutralized to pH 6.7 by 8 g L-1 CaCO3.
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Engineering components with high wear and corrosion resistant surfaces are essentially required to meet the ever-increasing demands for rapid developments of engineering applications upon the subjections to complex and/or harsh conditions. For example, there are needs for supporting anchor rods in to resist both corrosion and wear attacks during operation. In the present work, electroless plating was employed to prepare NiP coating on RB400 steel for improving surface performance and increasing usage of anchor rod in bracing project. Surface and cross-section morphologies of the obtained coating were measured by scanning electron microscope (SEM) and optical microscope (OM). Phase constitution and sectional element distribution were analyzed by X-ray diffraction (XRD) and glow discharge optical emission spectrometry (GDOES). A ball-on-disc type tribometer and electrochemical workstation were applied to make comparative evaluations on wear and corrosion resistance of anchor rod steel and NiP coating, respectively. The results showed that uniform and compact NiP coating was formed on RB400 steel anchor rod substrate. The surface hardness of substrate had tripled after electroless plating treatment. The obtained NiP coating indicated good antifriction effect and possessed excellent wear resistance, which was validated by friction coefficient, mass loss and worn-out appearance. The NiP coating exhibited higher corrosion potential and lower corrosion current density in comparison with bared anchor rod. The surface performance of anchor rod steel was significantly improved by NiP coating.
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The new corrosion protection technology with polyaniline, an Organic Metal (conductive polymer), is presented. It is based on an immense surface ennobling and the formation of a passivating metal oxide. The requirements for efficiently working coating systems, comprising the dispersed Organic Metal containing primer, eventually an intercoat, and a top coat, are characterized. An integrated 4-step-method ("scientific engineering") has been developed and is successfully used for the systematic development of such coating systems. The combination of the measurement of the open circuit potential, a new scratch test, EIS and SKP together are a powerful tool for predicting the results of accelerated corrosion tests and real-time corrosion prevention performance. Organic Metal coating systems are out-performing even the best conventional anti-corrosion coating systems.
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Polyaniline (PANI) coatings were electrosynthesised on steel samples (13% and 4.44% Cr) using sulphuric and phosphoric acids as supporting electrolytes. Protective properties of PANI coatings in the supporting electrolytes were investigated by monitoring the open-circuit potential vs. time, and by applying electrochemical impedance spectroscopy. PANI layers have been found to provide corrosion protection. Thicker PANI layers at 530 mV vs. Ag/AgCl (3 moldm−3 KCl) exhibit pure capacitive behaviour at low frequencies, and in addition a small resistance at high frequencies. Thinner layers at 530 mV exhibit a much higher resistance attributed to a higher degree of PANI-free electrode surface and/or to a significant amount of PANI transformed from emeraldine to leucoemeraldine form. The layer deposited in a phosphate solution appears to have better protective properties than the layer deposited in a sulphate solution. Therefore, PANI from phosphate solution was tested also in 0.1 moldm−3 HCl. However, in the chloride-containing solution, the time of protection was significantly shorter.
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Corrosion protection of metals can be obtained by coating them with polyaniline dispersions, resulting in a signifiecant and reproducible shift of the corrosion potential. Scanning electron micrograph indicate that the passivation is a multistep process, beginning with an etching stage in wh8ch grain boundaries become visible (see Figure). In the second step the metal surface is coated—non-electrochemically—with an oxide layer. The exact mechanism of formation of this layer remains to be explored.
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For the first time, it is shown that polyaniline can passivate various metals resulting in a significant increase of resistance against corrosion; it is shown that a surprising shift of the surface potential of these metals after polyaniline coating is the root cause for the passivation and corrosion resistance.
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Protective coating has been used widely for metal corrosion control. Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on a metal surface from an aqueous acid medium. In this study, an iron surface was coated by polyaniline thin film. While iron easily oxidizes in acid solutions, the electropolymerization reactions were carried out in dilute acidic media. Rust, fats, etc. on the surface of iron were removed by alkali-ethanol solution, dichloroethylene, and, finally, hydrochloride (HCl) solution (10%), respectively. Coating was carried out in different potential (1.0, 1.5, and 2.5 V). To observe the effect of elemental contents of iron samples, spectral analysis also was taken before electropolymerization. Especially, effects of chromium and nickel elements were investigated. Physical resistance of the coating was examined by “band test.” Dissolving and defective coatings were also tested in acidic solutions and common organic solvents. In addition, to observe the morphology of coating, photos of samples were taken by scanning electron microscope (SEM) and metal microscope (MM).
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The anti-corrosion performance of polyaniline coated mild steel samples exposed to artificial brine and dilute hydrochloric acid environments was evaluated. Samples of mild steel (UNS G10100) coated with polyaniline deposited from solution, and overcoated with an epoxy barrier paint, when scratched to expose precise areas of bare metal, exhibited corrosion rates in aqueous 3.5% NaCl solutions 2 times less, and in 0.1 N HCl solutions, 100 times less than observed on identical samples coated with epoxy paint alone. Mechanistic information, and quantitative corrosion rates were obtained by Tafel Extrapolation, Potentiodynamic Polarization, Galvanic Coupling and Electrochemical Impedance Spectroscopic techniques. These studies, in conjunction with surface analysis by ESCA and Auger techniques, indicate that the corrosion protection, even for exposed bare steel areas, occurs by the formation of passivating iron oxide (γ - Fe2O3 and Fe3O4) surface layers. The formation of these specific oxide layers occurs when the polyaniline is galvanically coupled to the steel. This is evident by the fact that the dimensions of the exposed bare steel area that can be protected in a scratch can be large, but are limited in each corrosion environment.
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The organic metal polyaniline (PAni) was found by us some years ago to be a powerful corrosion protection agent. The properties of the new PAni containing primer CORRPASSIVTM sealed with different top coats are characterized and compared with top coated probes using no or a conventional zinc primer. The combination of measurements of salt spray test, electrochemical impedance spectroscopy (EIS) and scanning Kelvin-probe (SKP) for testing the results of accelerated corrosion are presented.
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Composites of polyaniline conducting polymers (polyaromatic amines) with synthetic polymers such as polyamides (nylons) can be processed from formic acid solvent through cast method. Formic acid was found to be a good solvent for preparation of polyaniline/nylon composites (PAn/Ny) as free standing films or coating on the surface of different inert substrates. The preparation conditions of PAn/Ny composite were optimized with regard to the mechanical properties and electrical conductivity. Chemical polymerization of polyaniline polyamide (nylon) composites with the procedure described in this paper provides the best way in order to prepare PAn/Ny composite membranes with high conductivity, uniformity and homogeneity. The procedure described can also be considered the only way for preparing PAn/Ny composites as coated on the surface of inert and conducting substrates such as glass or paper in order to make them conductors or semiconductor materials.
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Some polypyrrole free standing films or membranes doped with different electrolytes (aromatic sulphonated) were prepared from aqueous monomer solutions in order to investigate the effect of thermal treatment on their electrical conductivity. It was found that the nature of counterion has the most important effect on determining the electrical conductivity and stability of conductivity when the polymer is exposed to high temperatures. However, mild heating can improve conductivity of polypyrrole conducting polymers. In order to carry out thermal effect studies on conductivity and measure the thermal stability of the PPy film, a variety of anions were examined. It was found that when polypyrrole is being doped with aromatic sulphonates (mainly benzene or naphthalene sulphonates) as counterions, it produces flexible and smooth films that can be readily detached from working electrode as membrane and they have good mechanical properties. Other counterions such as inorganics (e.g., Cl-, SO42-), aliphatic surfactants (e.g., DS), and polymerics (PVS) produce films that are either impossible to remove from working electrode, or give brittle, and rough films.
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Introduction Wet corrosion Thermodynamics - equilibrium potentials Electrode kinetics Passivity Corrosion types with different cathodic reactions Different corrosion forms classified on basis of appearance of attacks Corrosion in different environments Corrosion testing and monitoring Corrosion prevention
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A series of polyaniline films have been coated on electrodes by chemical and electrochemical means in order to investigate the thermal stability of the electroactivity in air and nitrogen atmospheres. Polyaniline was also synthesized chemically and cast as a membrane (thick film). It was found that the electroactivity and conductivity of the films was stable up to 150°C. Exposure to higher temperatures leads to a decrease in electroactivity and conductivity, although use of a nitrogen atmosphere had less effect on the properties. Thermogravimetric analysis profiles confirmed that the polymer was stable to above 350°C. The changes in the electroactivity may be attributed to morphological (annealing) effects in the polymer and to loss of moisture and dopant ions.
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A series of electrochemical measurements, including corrosion potential, corrosion current, Tafel's constants and polarization resistance, have been made on polyaniline-coated cold rolled steel specimens under various conditions. Both the base and acid-doped forms of polyaniline were studied. The base form of polyaniline was found to offer good corrosion protection. This phenomenon may not originate merely from the barrier effect of the coatings, because nonconjugated polymers such as polystyrene and epoxy did not show the same electrochemical behaviour.
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The present work addresses in a concise and sequential way the updated structure of intervention for minimising the atmospheric corrosion of steel, considering matters such as the mechanisms of atmospheric corrosion of iron, the different protection techniques and respective influential factors, and refers to aspects related with the specifications for new steelworks and maintenance. It also establishes the essential guidelines for setting up a “Certification Scheme for Anticorrosive Paint Systems”, based on existing and emerging international standards and results of Ibero-American R&D Projects, whose extended application, in the different countries, would allow the high cost of atmospheric corrosion of steel structures to be drastically reduced.
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The corrosion performance of steel coated with co-polyamide polymers and polyaniline in neutral salt spray (NSS) and accelerated corrosion testing is presented. A coating of the nylon polymer on steel is not sufficient to prevent corrosion in a chloride medium, the underlying steel showing signs of corrosion after only three days in the NSS environment. Open-circuit potential measurements indicate the steel is corroding forming soluble ferrous and ferric oxy-complexes. Polyaniline by itself is also insufficient in inhibiting corrosion on steel. A synergy exists between an under-layer of polyaniline and a top layer of the nylon coating in minimizing corrosion.
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Polyaniline has been synthesized chemically and cast from 1-methyl-2-pyrrolidone (NMP) solution over iron samples. A series of electrochemical measurements, including corrosion potential and corrosion current has been made on polyaniline-coated iron samples in various environments. Results showed that polyaniline can offer some degrees of protection in the corrosive environments. Protective properties of the conducting polymer were compared with a conventional polymer such as polyvinyl chloride (PVC). Comparative experiments revealed that emeraldine base form of polyaniline has better protective properties.
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Electrochemical techniques are described of direct use to chemical processors for optimum material selection in designing and maintaining new plants as well as corrosion monitoring and control in operating existing plants. Reference is made to the three corrosion forms most responsible for failures in chemical equipment, i.e.: general corrosion, localised corrosion, and stress-corrosion cracking. Practical examples are given of successful industrial application of electrochemical methods: 1) for controlling active corrosion of a stainless alloy in pressure reactors operated with hot sulphuric acid solution and 2) for preventing stress corrosion cracking of a low-alloy steel in a pressure absorption tower operated with hot alkali carbonate solution.
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Studies using electrochemical impedance spectroscopy (EIS) were carried out on an iron disk electrode in 0.01 mol/L sodium hydroxide (NaOH) + x ppm silica (SiOâ) (x = 250, 500, and 750 ppm) polarized at 300 mV{sub SCE} to determine the effect of silicate on passive films anodically formed on iron in alkaline solutions. EIS proved silicate increased film resistance (R{sub f}), decreased its capacitance (C), and affected the kinetics of interfacial electrochemical reactions, leading to an increase in the charge-transfer resistance (R{sub t}), which depended upon silicate concentration and polarization time.
Article
Purpose – This paper aims to investigate the protection efficiency of a thin film of electrochemically synthesized conducting polymers, such as poly m‐toluidine, poly N‐methyl aniline, and its copolymer, poly (aniline‐co‐N‐methyl aniline) (PANINMA), on plain carbon steel in 0.1 M HCl. It also attempts to compare the protection efficiency of these compounds with polyaniline (PANI)‐coated carbon steel. Design/methodology/approach – The green coloured and adherent coatings were obtained by cyclic voltammetry during sequential scanning of the potential region between −0.6 and 1.6 V at a scan rate of 10 mVs⁻¹. Potentiodynamic polarization measurement (DC) was used to obtain an estimate of the corrosion rate and protection efficiency for these electrodeposited polymers on the carbon steel. Scanning electron micrographs (SEM) also were obtained to characterize the deposited coatings. Findings – It was observed that these polymer coatings showed better protection efficiency than the PANI coating. Of the compounds studied, the copolymer PANINMA coating showed higher protection efficiency than other coatings. The SEM observations revealed that the compact continuous dense morphology of PANINMA provided better protection than other coatings. Originality/value – This paper explains the protection efficiency of the substituted and copolymer coatings of PANI on carbon steel.
Article
Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on iron and mild steel in a one-step process from an aqueous oxalic acid medium which passivates substrates. Homogeneous and strongly adherent films of controlled thickness can be deposited either in the potentiodynamic or galvanostatic modes. These films are characterized by IR, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC) and matrix-assisted UV-laser desorption ionization (MALDI) techniques, and have a structure similar to that of PANi deposited on platinum. Iron samples coated with PANi exhibit much better protection against corrosion in an acidic solution (0.4 M NaCl + 0.1 MHCl) than the polypyrrole-coated ones. Attempts to grow PANi films on zinc or zinc—nickel alloy in oxalic acid were unsuccessful because the formation of insulating layers prevents electropolymerization.
Article
This study examines the use of polyaniline (PANi), poly(2-toluidine) (PT), and poly(aniline-co-2-toluidine) (co-PT) for corrosion protection of 304-stainless steel (SS) in 0.5 M HCl solution. The PANi, PT, and co-PT coatings were synthesized on SS substrates under cyclic voltammetric (CV) conditions from acetonitrile solution using tetrabuthylammonium perchlorate (TBAP) as supporting electrolyte and perchloric acid (HClO4) as acid. These coatings were characterized by CV, FTIR, and UV–vis spectroscopy. The ability of PANi, PT, and co-PT to serve as corrosion protective coatings for SS was examined by open circuit potential-time (Eocp-time), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The results of this study reveal that PANi, PT, and co-PT acts as corrosion protective coatings on SS and every coating gives protection efficiency of greater than 80% after 48 h of immersion in corrosive test solution.
Article
The effect of solution temperature on the mass transport properties of PPy conducting polymers doped with different dopants such as p-toluene sulfonate (PTS−), dodecyl sulfate (DS−) and dodecyl benzene sulfonate (DBS−) counterions was investigated. The electrochemical quartz crystal microbalance (EQCM) technique was employed to investigate the ion-exchange properties of the polymers at different solution temperatures. It was found that the size of the counterion employed during synthesis had a determining effect on the ion-exchange properties of PPy conductive electroactive polymers. The ion-exchange properties of PPy are also affected by the solution temperature.
Article
Corrosion of steels causes a loss of about 121 billion dollars annually and half the iron produced at present is used for the replacement of the existing deteriorated structures. Corrosion, being an electrochemical phenomenon, can be tackled through the use of electrochemistry and conducting polymers. Stainless steels can be passivated by applying a potential of about 0.1 V versus SCE and a current of about 100 μA/ cm2. These can be provided by a conducting polymer, emeraldine, which can be applied chemically on the surface of the stainless steel. Pre-treatments with some chelating agents can inhibit the corrosion of stainless steel from 0.1 M HCl for about 1 month.
Article
Growing environmental concerns regarding the use of heavy metals in coating formulations has led to a new coating strategy employing inherently conducting polymers (ICP) as a key component. ICPs (such as polyaniline, polypyrrole and polythiophene) are electrically conductive owing to a system of conjugated double bonds. Observations of metal passivation complement this conductive nature and offer a viable alternative to traditional corrosion protection (1–8). A key potential advantage that the ICP coating technology offers is toleration of pin holes and minor scratches. The basis for this argument is that, since the ICP coating is conductive, the entire coating acts to passivate any areas of exposed metal. This paper describes a model for polyaniline (PANI) corrosion protection and presents data which clearly demonstrate significant corrosion protection in a salt fog environment. ESCA and electrochemica data are presented which show that an Fe-PANI complex is formed in the process of coating steel with PANI. The Fe-PANI complex is shown to catalytically reduce oxygen. Preliminary electrochemical impedance results are also presented which show an additional time constant at 20 kHz, which appears to correlate with the effectiveness of PANI toward corrosion protection.
Article
Polyaniline epoxy blend coatings on mild steel have been studied in neutral, acidic and alkaline solutions with various electrochemical methods. It has been found that coatings containing emeraldine base provide better corrosion protection in NaCl solution than coatings based on conducting polyaniline. Good corrosion protection by emeraldine base was observed even when a hole was made to the coating. In HCl solution protonated polyaniline gave better performance.
Article
Conducting/electroactive polypyrrole polymers are synthesized electrochemically on glassy carbon in various electrolytes (counterions). The polymers' electroactivity is measured using cyclic voltammetry. The electrolytes are chloride, nitrate, p-toluene sulfonate, dodecyl sulfate, and dodecylbenzenesulfonate of sodium and potassium ferrocyanide. It is found that the electrolyte (dopant) markedly affects the redox behavior of the polypyrrole films.
Article
The methods of polarization resistance and impedance are used extensively in the group of the electrochemical Methods. These methods assume that the corrosion rate and various characteristics of the metal-medium corrosion systems, such as polarization resistance and the resistance to charge transfer, respectiveiy, are linked by direct relationships. The polarization resistance method (PRM) was developed by Stern [3] who introduced the concept of linear polarization for describing the linear dependence between the polarization current density Ai and the displacement of the potential system bE in the range of the corrosion potential Eco r (Fig. la)
Article
This paper reviews the literature describing the effects of conducting polymer coatings on the corrosion rate of ferrous alloys (iron, steel and stainless steel). The literature is interpreted in terms of the proposed mechanisms of corrosion protection: barrier, inhibitor, anodic protection and the mediation of oxygen reduction. The most intriguing aspect of the reported literature are the studies demonstrating corrosion protection when deliberate defects were introduced into the coating to expose the bare metal. These studies show that protection afforded by conducting polymer coatings is not due to simple barrier protection or inhibition alone. Many studies illustrate that the polymer/metal interface is modified to produce passivating oxide layers and that charge transfer reactions occur between the metal and polymer. These studies support the proposed anodic protection mechanism, as do the reports of significant ennoblism. On the other hand, there is considerable variation in the reported shift in corrosion potential and these highlight the influence of substrate preparation, coating composition and mode of application and the nature of the electrolyte on the corrosion protection provided by the conducting polymer. For example, the evidence suggests that the emeraldine base form of polyaniline is superior to the emeraldine salt in terms of corrosion protection for steel. However, the number of direct comparisons is small and the reasons for the differences are not well understood. Also not well understood are the role of the counterion release and local pH changes on pinhole protection. It is also argued that the conducting polymer reduces the likelihood of large increases in pH at the polymer/metal interface and so stabilizes the coating against cathodic disbondment. Further work is clearly needed to increase the protection period by further studies on the corrosion protection mechanism so that the polymer composition and processing methods may be optimized.
Article
There is an intensive effort underway to develop new corrosion control coatings for structural metals. In part, this effort has been motivated by the desire to replace chromium(VI)-containing coatings currently used for corrosion control of iron and aluminum alloys. Cr(VI) has been shown to be hazardous to the environmental and to human health, and its use in many countries will be sharply curtailed in the coming years. Electroactive conducting polymers (ECPs) represent a class of interesting materials currently being explored for use in corrosion control coating systems, possibly as a replacement for Cr(VI)-based coatings. The electroactivity and the electronic conductivity (or semiconductivity) of ECPs set them apart from traditional organic coatings. As with chromate, interesting and potentially beneficial interactions of ECPs with active metal alloys such as steel and aluminum are anticipated, with concomitant alteration of their corrosion behavior. A review of this active research area will be presented in two parts. Here in Part 1, a general introduction to the topic of corrosion control by ECPs will be presented, including an overview of corrosion and its control by traditional methods, an introduction to ECPs and their properties, and a discussion of the processing issues surrounding the use of ECPs as coatings. Part 1 also includes a review of the literature on the use of ECPs as coatings (or components of coatings) on non-ferrous active metals, principally aluminum and aluminum alloys, although some work on zinc, copper, silver, titanium and silicon will also be described. In Part 2 of this review (to be published in the next issue of this journal), the rather extensive literature on the use of ECPs for the corrosion control of ferrous alloys (steels) will be reviewed.
Article
The present work was undertaken to study the corrosion behaviour of conducting polymer coating on ferrous material. The synthesis of polyaniline (PAni) powder, its characterization, blending and coating formulation are described in details. The yield of synthesized polymer was approximately 90% with a conductivity of 0.20–0.40 S/cm. The coating was formulated by incorporating this PAni powder as pigment. The coating conductivity increased with increase in the solid concentration and saturated in the range of 10–15 wt.%. The results of the corrosion tests on PAni coated steel substrate with 1–50 μm coating thickness exposed to 3.5% NaCl solution were also presented. The corrosion resistance of PAni coated steel was found to be more than 10–15 times higher than the bare steel. Electrochemical impedance spectroscopy study revealed that a continuous charge transfer reaction across the metal–coating interface was responsible for the increase in coating capacitance and decrease in polarization resistance. The potentiodynamic study also showed that the current density significantly decreased in PAni coated steel in comparison to bare steel.
Article
The electrodeposition of protective polyaniline (PANi) films on mild steel from aqueous oxalic acid is reported. The electropolymerization of aniline occurs on a surface passivated by the precipitation of an Fe(II)-oxalate layer and leads to strongly adherent films with a controlled thickness and with the same structure as the idealized emeraldine base. When they are dipped in an acidic solution (0.4 M NaCl + 0.1 M HCl) the PANi-coated iron samples exhibit very good protection against corrosion and are much more effective than polypyrrole coated ones.
Article
A general review of the chemistry and corrosion control properties of electroactive polymers will be presented. These polymers are also known as conductive polymers (CPs), and this term will be used throughout this article. This paper will focus on both the synthesis of applicable CPs used for corrosion protection in various environments and their potential benefits over common organic barrier coatings.
Article
In the present study potentiodynamic polarisation curves were obtained for carbon and stainless steel in contact with 3% sodium chloride aqueous solution saturated with air in order to evaluate the capacity of polyaniline in the emeraldine oxidation state to protect the surface against corrosion processes. A high stability of the PAni films was observed with a gain of the corrosion potential around 270 mV more positive in the substrate covered with PAni than in the case without it. Corrosion of steel could be prevented using the conducting polymers as a protective layer.
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