Polypyrrole films on nickel-plated copper

Polypyrrole (PPy) film was synthesized on nickel-plated copper electrodes, from monomer containing 0.2 M ammonium oxalate solution. The thickness of galvanostatically deposited nickel layer was 2 μm, while 0.80 μm thick polymer film was obtained by using cyclic voltammetry technique. The protective behavior of PPy modified nickel coating has been investigated, against copper corrosion in 3.5% NaCl solution. For this aim, ac impedance spectroscopy, the anodic polarization curves and open circuit potential–time (E_ocp–t) diagrams were utilized. It was shown that PPy modified nickel coating could provide important protection to copper for considerable periods, in such aggressive medium. The thin polymer film constituted a physical barrier on top of nickel layer against the attack of corrosive environment for a certain period. Also, it was found that the thin PPy film could increase the protection efficiency and lifetime of nickel coating, by its catalytic behavior on formation of NiO layer.     

Electrochemical synthesis of polyindole on 304-stainless steel in LiClO4–acetonitrile solution and its corrosion performance

The use of electrochemically synthesized polyindole (PIN) film was investigated for protective coating on 304-stainless steel (SS). Polyindole was deposited via anodic oxidation of the corresponding monomer, indole in acetonitrile (ACN) solution containing LiClO₄. It provided an adherent and stable coating on SS. The corrosion performance of coated and uncoated SS was investigated in 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open-circuit potential–time (E_ocp–t) diagrams. These tests demonstrated that PIN coating provided important barrier effect to SS for important immersion times in aggressive medium.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

The corrosion protection of mild steel by single layered polypyrrole and multilayered polypyrrole/poly(5-amino-1-naphthol) coatings

Electrochemical synthesis of polypyrrole (PPy) and top coat of poly(5-amino-1-naphthol) (PANAP) on PPy films from oxalic acid solution was achieved on mild steel (MS) by cyclic voltammetry technique. The morphology and the structure of the films were investigated by scanning electron microscopy (SEM). The corrosion performance of this multilayer coating and single PPy coating were investigated in 3.5% NaCl solution by using open circuit potential (E_ocp)–time curves, polarization curves and electrochemical impedance spectroscopy (EIS). It was found that the multilayer PPy/PANAP coating could provide much better protection than single PPy coating for corrosion of MS. It was observed that corrosion performance of coatings was increasing with immersion period. This was explained by auto-undoping properties of PPy coatings during immersion in corrosive solution. The improved corrosion performance in the presence of PANAP top coat on PPy was explained by increase in barrier effect of bilayer films.     

Role of oxygen in the galvanic interaction between polypyrrole and aluminum alloy

Conjugated polymers continue to be of interest as possible corrosion-control coatings for metal alloys. In this work, electrochemical interactions between polypyrrole (PPy) films and the aluminum alloy 2024-T3 (AA) were investigated by electrochemical polarization and galvanic coupling techniques in dilute Harrison's solution (0.35 wt% (NH₄)₂SO₄, 0.05 wt% NaCl). A two-compartment electrochemical cell was used for the galvanic coupling measurements which permitted assessment of the role of dissolved oxygen by segregating the PPy film and AA in individual compartments. Electroactive 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt (BDA or Tiron) and electroinactive benzene-1,3-disulfonic acid, disodium salt (BDS) were used as dopants to study the mediating effect (if any) of BDA on the coupling behavior. The results indicate that oxygen reduction mediated by the PPy coating dominates the coupling interaction. The electrochemical polarization state of AA 2024-T3 in a pinhole simulating a PPy coating defect was characterized by the potential measured immediately after decoupling, by the anodic hydrogen evolution, and by galvanodynamic polarization. The results support the conclusion that the alloy in the coating defect was electrochemically active, not passive, during coupling with PPy. The anodic protection model commonly accepted for ferrous metals does not appear to apply to AA 2024-T3.     

Anticorrosive properties of polypyrrole films modified with zinc onto SAE 4140 steel

Polypyrrole (PPy) films modified with zinc were electrosynthesized onto SAE 4140 steel in presence of bis(2-ethylhexyl) sulfosuccinate (AOT). The Zn and PPy electrodeposition was realized by using cyclic voltammetry at different temperatures. The corrosion protection properties of the films were examined in chloride solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The obtained results indicate that the presence of Zn in the polymer matrix improves the anticorrosive performance of PPy films. The best anticorrosion efficiency was obtained for the coatings modified at 20 °C which provided anodic protection to the steel substrate for a long period of immersion in chloride solution. Cathodic protection was observed when the electrodeposition temperature was increased. Adherence and anticorrosive properties declined sharply for the coatings electrosynthesized at 5 °C.     

Polypyrrole coatings for corrosion protection of Al alloy2024: influence of electrodeposition methods,solvents, and ZnO nanoparticle concentrations

Since ZnO nanoparticles increase the electrical conductivity of the polypyrrole (PPy) coatings, an investigation was carried out to evaluate the effect of ZnO nanoparticles loading on the corrosion protection performance of PPy coatings on AA2024 Al alloy in 3.5% NaCl solution. At first, some measurements were carried out to find the best experimental conditions containing the electrodeposition method, electrosynthesis solvent composition, and ZnO nanoparticles’ concentration for preparing the optimum PPy coating on Al alloy2024. Three different methods of electrodeposition, namely: cyclic voltammetry, galvanostatic, and potentiostatic techniques were analyzed. The anti-corrosion performance of the PPy coatings was evaluated by electrochemical impedance spectroscopy and Tafel polarization methods. The PPy prepared by potentiostatic method exhibited the best performance against corrosion of Al alloy2024 in 3.5% NaCl solution. Then, different mixtures of H₂O/ethanol were tested as electrosynthesis solvents for preparation of PPy coatings on the alloy by optimized electrodeposition mode (i.e., potentiostatic). In evaluation of the prepared coatings, the pure water was introduced as the optimum solvent in electrodeposition of PPy. The investigation of different ZnO nanoparticles’ concentrations proved that the PPy coating containing 0.025% ZnO nanoparticles was the optimum coating against the corrosion of Al alloy in NaCl solution. Finally, the long-term evaluation of the corrosion protection performance of the coatings revealed that the optimum coating provided suitable protection against corrosion up to 14 days after immersion.

     

Corrosion protection of iron by polystyrenesulfonate-doped polypyrrole films

Electropolymerized polypyrrole (PPy) has been studied as a protective coating for iron in NaCl 3% corrosive medium. The protection mechanism is of the galvanic type, and the main cause for the loss of protection is the progressive invasion of the film by chloride anions. To reduce exchanges between PPy counter-ions and chloride anions, a composite polyanions/PPy film was used. Polystyrenesulfonate was chosen as a large size counter-ion which could be trapped in the polymer matrix. Due to the negligible mobility of these anions, the film permselectivity changed from anionic to cationic. A significant improvement in PPy film protection efficiency was obtained.     

Effect of external bias voltage and coating thickness on the photocatalytic activity of thermal sprayed TiO2 coating

TiO₂ coatings of different thickness were prepared by a thermal spray process. It was found that the external bias applied to the as-sprayed TiO₂ coating could significantly improve its photocatalytic performance, which was characterized by decomposition of methylene blue (MB) solution. The decomposition efficiency increased with increasing external bias voltage. However, for voltage greater than 15 V, the decomposition efficiency remained constant. The TiO₂ coating with a thickness of 6 μm showed the best photocatalytic performance under an external bias voltage of 15 V.     

Synthesis of Na0.5K0.5NbO3 Piezoelectrics by a Solution Coating Approach

The solution coating method is shown to provide more homogeneous mixing of the starting powders and purer (Na_0.5K_0.5)NbO₃ (NKN) powder than the conventional method thereby rendering cold isostatic pressing unnecessary. Sintering NKN with potassium copper niobate (KCN) by uniaxial pressing gave a relative bulk density of 92%, d ₃₃ coefficient of 112 pC/N and a loss factor of 1% after 6 h at 1100°C. In contrast, the conventional method yielded 84% relative bulk density and a 31% loss factor after 6 h at 1100°C and the sample was too porous to allow for dielectric and piezoelectric measurements.     

Water uptake of epoxy coatings modified with γ-APS silane monomer

Epoxy resin was modified by a silane monomer, γ-aminopropyltrimethoxy silane (γ-APS), and was used as the protective coatings for LY12 aluminum alloys. The aim of the modification is to reduce the water uptake of polymeric coatings. The water absorption of coatings was measured by coating capacitance method in 3.5 wt.% NaCl aqueous solution. The result indicates that water uptake of epoxy coatings modified with 1.0 wt.% γ-APS decreases compared with pure epoxy coatings, whereas larger amounts of sliane result in the deterioration in performance against water permeation, due to the excessive consumption of epoxide group in epoxy resin by amino-group in silane agent, thus reduce the cross-linking of epxoy coating as a result of presence of excessive curing agent (polyamide). T_g of silane-modified coatings increases slightly after immersion, extremely contrasting with that of pure epoxy coating, which was observed to decrease significantly after water permeation. The formation of Si–O–Si structure resulting from the hydrolysis and condensation of silane components during the immersion in aqueous media may be a reasonable explanation for the abnormal change in T_g of silane-modified coatings. In addition, all silane-modified coatings display better protection performance, which is characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface.     

Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution

The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1 M sulfuric acid solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm⁻². Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1 M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.     

Highly transparent and organosoluble polyimides derived from 2,2′‐disubstituted‐4,4′‐oxydianilines

Polypyrrole (PPy) and Polypyrrole‐ZnO (PPy‐ZnO) nanocomposites were electrodeposited on mild steel and its corrosion protection ability was studied by Tafel and Impedance techniques in 3.5% NaCl solution. Pure Polypyrrole film was not found to protect the mild steel perfectly but the coating with nano‐sized ZnO (PPy‐ZnO) has dramatically increased the corrosion resistance of mild steel. Electrochemical Impedance Spectroscopy (EIS) measurements indicated that the coating resistance (R_coat) and corrosion resistance (R_corr) values for the PPy‐ZnO nanocomposite coating was much higher than that of pure PPy coated electrode. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication of ZnO-functionalized polypyrrole microcomposite as a protective coating to enhance anticorrosion performance of low carbon mild steel

In the present work, PPy, ZnO, and polypyrrole/zinc oxide (PPy/ZnO) microcomposites (1, 2, and 5 wt%) were prepared and their properties have been tuned for anticorrosion applications on low carbon mild steel. The synthesized products: ZnO, PPy, and composites were characterized by various sophisticated analytical techniques such as XRD, FTIR, Raman, FESEM, EDX, UV–VIS, TGA, and BET. The band frequencies observed at 480 and 588 cm⁻¹ in FTIR spectrum correspond to stretching vibrations of Zn-O and N-H bonds, respectively, broadening of the bands in the composites indicate strong interactions between ZnO and PPy matrix. The potentiodynamic polarization study of PPy and PPy/ZnO composite was carried out in 3.5% NaCl solution to investigate the corrosion resistance efficiency. PPy/1 wt% ZnO (I_corr = 190 nA) composite coating on low carbon mild steel was observed to exhibit best corrosion protection property compared to PPy (121 μA), 2 and 5 wt% ZnO (242, 295 nA) composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48319.     

Electrodeposition of casein coatings on zinc alloy

The electrochemical behavior of zinc in caseinate solution at pH 10 was investigated. Current–potential curves and weight loss measurements by atomic absorption showed that the anodic dissolution rate of the metal is higher than that obtained in NaOH solution (pH 10). Anodic treatment of zinc alloy at constant potential in such solutions induces the growth of a coating which presents, after drying, strong adherence and a good protection effect in aggressive solution (0.2 M NaCl+0.2 M Na₂SO₄). IR and ESCA spectrophotometric analysis showed that the zinc ions mainly participated in the growth of a casein coating, probably in a complexed form.     

Electrocatalytic oxidation of p-nitrophenol from aqueous solutions at Pb/PbO2 anodes

In this work, the elimination of p-nitrophenol (p-NPh) from aqueous solutions by electrochemical oxidation at Pb/PbO₂ anodes was investigated. The process was studied under galvanostatic polarization mode in acidic and alkaline media, as a function of the temperature (20, 40 and 60 °C) and of the anodic current density (J = 10, 20 and 30 mA cm⁻²). In acidic media (0.5 M H₂SO₄), the oxidation process allowed a 94% p-NPh conversion in 7 h, at 20 °C and with J = 20 mA cm⁻², with a wide distribution of degradation products (in particular: 39% p-benzoquinone and 26% hydroquinone, as given by a mass balance at the above electrolysis time). Under these conditions, the current efficiency for the substrate oxidation was 15.4% ([Ah L⁻¹]_exp = 7 versus [Ah L⁻¹]_theo = 1.08 Ah L⁻¹). In alkaline media (0.1 M NaOH, pH 8.5), the most effective p-NPh elimination (97%) was obtained at 60 °C, 20 mA cm⁻² and 420 min of electrolysis time, again with the production of p-benzoquinone and hydroquinone (52.7 and 15.1%, respectively). Under the latter conditions, an almost complete chemical oxygen demand (COD) abatement was attained, with a high level of p-NPh mineralization (>80%), a yield of p-NPh conversion greater than 95% and a scarce formation of aliphatic acids (most probably maleic acid). From the degradation curves ([p-NPh] versus t), in both acidic and alkaline media, the UV analyses and/or COD measurements, a complete oxidation of aliphatic acids to form CO₂ could be predicted for electrolysis time >420 min, according to a suggested oxidation pathway.     

Remediation of chromium(VI) at polypyrrole-coated titanium

The application of conducting polypyrrole (PPy) and polyaniline (PAni) coated substrates in remediation of chromium, Cr(VI), is an area of considerable interest. Here, we discuss the implementation of PPy-coated titanium as a new material for the reduction of Cr(VI) to the less toxic trivalent state, Cr(III). An alkaline-peroxide based etching process was used to ensure the adhesion of the PPy coatings to the underlying titanium. The PPy films showed excellent resistance to acidic Cr(VI) solutions and remained adherent after continuous exposure to the solutions. In order to optimise the remediation process a number of experimental parameters were investigated, including the thickness of the PPy coating, the reduction potential used in pre-treatment of the PPy and the degree of solution agitation. The durability of the materials on exposure to the Cr(VI) test solutions made them suitable for repeated remediation experiments. Following several test-runs, the cleanup efficiency of the material was found to decrease slightly, however, increasing the exposure/experiment time resulted in significantly improved cleanup ability.     

Electrochemical hydrogenation of dinitrogen to ammonia on a polyaniline electrode

The fixation of molecular nitrogen (dinitrogen) to ammonia was investigated depending on applied potential, pressure and temperature on a Pt-plate coated with polyaniline (PAn) film in methanol/LiClO₄/H⁺ solution. The reaction product was only ammonia with a maximum concentration of ca. 57 μmol L⁻¹ after 5 h electrolysis time. Maximum current efficiency for ammonia formation was ca. 16%. The optimum film thickness was found to be 1.5 μm, N₂-pressure 50 bar and an optimum electrolysis potential was only −0.12 V (NHE).     

Electrochemical synthesis of poly(5-nitroindole) on 316L-stainless steel in LiClO4-acetonitrile solution and its corrosion performance

The preparation of poly(5-nitroindole) (P5NI) coating was achieved on 316L-stainless steel (SS). Poly(5-nitroindole) was deposited via anodic oxidation of the corresponding monomer in acetonitrile (ACN) solution containing LiClO₄. The influence of P5NI coating against SS corrosion was studied in 3.5% NaCl solution by electrochemical impedance spectroscopy (EIS), anodic polarization curves and the open circuit potential–time (E_ocp–t) diagrams. The results obtained suggest that P5NI coating forms a sacrificial layer but the efficiency against corrosion is limited with increasing time.     

Corrosion protection with zinc-rich epoxy paint coatings embedded with various amounts of highly dispersed polypyrrole-deposited alumina monohydrate particles

Active anodic zinc content below 90 wt.% does not support sufficient electrical contacts but higher contents cause high porosity of traditional liquid zinc-rich paints (ZRPs). To resolve this problem, our proposal is the application of highly dispersed polypyrrole (PPy) coated alumina inhibitor particles (PCAIPs) in zinc-rich paint compositions. Using these nano-size inhibitor particles at concentrations from 4.55 to 0.85 wt.%, hybrid paints were formulated with zinc contents ranging from 60 to 85 wt.% at the same time. Submicron morphology and nano-scale structure, spectroscopy characteristics and electrochemical properties of the PCAIPs were studied by transmission electron microscopy (TEM) and rheology, Fourier-transform infrared spectroscopy (FT-IR) and cyclic voltammetry (CV) in first part of the work. In the second part, electrolytic corrosion resistivity of two sets of paint coatings were salt-spray chamber and immersion tested with 5 wt.% aqueous solution of sodium chloride. Active corrosion prevention ability of the salt-spray tested coatings was evaluated in compliance with ISO recommendations. Dielectric properties of the coatings during the immersion tests were monitored by electrochemical impedance spectroscopy (EIS). Corrosion tested area of the coatings was investigated by glow-discharge optical emission spectroscopy (GD-OES) to disclose infiltration of corrosive analytes and oxygen enrichment in the cross-section of the primers in comparison with their pristine states. Morphology of the zinc pigments was examined by scanning electron microscopy (SEM), and quality of steel specimens and the interfacial binder residues by X-ray photoelectron spectroscopy (XPS) as well as FT-Raman and Mössbauer spectroscopy. The results of both types of corrosion tests evidenced efficient utilisation of sacrificial anodic current for galvanic protection and improved barrier profile of the hybrid coatings, along with the PCAIP inhibited moderate self-corrosion of zinc. As a result of well balanced active/passive function, the hybrid coating containing zinc at 80 wt.% and PCAIPs at 1.75 wt.% embedding PPy at 0.056 wt.% indicated the most advanced corrosion prevention. Galvanic function of the hybrid paints is interpreted on the basis of size-range effect and spatial distribution of the alumina supported PPy inhibitor particles and basic electrical percolation model considerations.