Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

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.     

Influence of pH on the synthesis and properties of polypyrrole on copper from phytic acid solution for corrosion protection

Polypyrrole (PPy) films were deposited on copper from “green” inhibitor of phytic acid solution for corrosion protection of copper. The corrosion protection property of the PPy layer was studied by an immersion test in a NaCl aqueous solution. The polymerization process of PPy on copper changed with the pH values of phytic acid solution and current density applied. When one oxidized bare copper in phytic acid solution at various pHs containing pyrrole monomer, a thin layer consisting of complex compound of Cu-phytate was firstly formed, followed by the formation of the PPy layer doped with phytate anion on the complex compound layer. The complex compound layer passivated the copper surface and its thickness increased with the lower pH value of the solution and the lower current density applied. It was found that the PPy coating prepared in the phytic acid solution at pH 4 exhibit the most protective property against copper corrosion.     

The use of polyindole for mild steel protection

Synthesis of polyindole was achieved on mild steel electrode previously coated with a very thin polypyrrole layer (PPy). Cyclic voltammetry technique was used for both syntheses; oxalic acid solution was used for synthesis of primer PPy coating and polyindole film (PI) was obtained from LiClO₄ containing acetonitrile medium. The corrosion performance of this PPy/PI coating was investigated properly in 3.5% NaCl solution by using anodic polarization and open circuit potential (E_ocp)–time curves and electrochemical impedance spectroscopy (EIS). This coating exhibited excellent barrier efficiency for a long time (about 190 h) and it was also able to provide a certain anodic protection. After 240 h of immersion time in corrosive test solution, the protection efficiency value was determined to be 98.9%.     

Improvement of polypyrrole films for corrosion protection of zinc-coated AZ91D alloy

To improve the protection against the corrosion of AZ91D magnesium alloy provided by conducting polypyrrole (PPy) films, optimization of the electrochemical synthesis of the PPy film was investigated. The bi-layered PPy film was prepared under constant current control, first in a sodium tartrate solution containing molybdate and second in a sodium dodecylsulfate (DS) solution (after the AZ91D alloy was covered by zinc electroplating). Corrosion testing of the zinc-coated AZ91D alloy covered with the PPy film was performed in 3.5% NaCl solution. The more protective PPy film doped with tartrate ions (PPy-Tart film) was formed by the lower current density (CD). Doping of molybdate ions (MoO₄²⁻) into the PPy-Tart film significantly improved its corrosion protection properties. When the PPy-Tart-MoO₄ layer was covered by an outer PPy layer doped with DS ions, the corrosion protection was further improved. The imposition of ultrasonic waves during the electropolymerization of the inner PPy-Tart-MoO₄ layer was effective in the improvement of corrosion protection. The bi-layered PPy-Tart-MoO₄/PPy-DS film prepared under ultrasonic irradiation maintained the zinc-coated AZ91D alloy in the passive state during the corrosion test in NaCl solution for 221 h, during which no corrosion products appeared.     

Zinc deposited polymer coatings for copper protection

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

Electrochemical synthesis of polypyrrole (PPy) and PPyǀmetal composites on copper electrode and investigation of their anticorrosive properties

This study reports corrosion protection behaviour of various metal cations electrodeposited onto polypyrrole (PPy) coated copper (Cu) electrode. Before electropolymerization of pyrrole, the Cu electrode was passivated in 0.1 M oxalic acid via cyclic voltammetry method. After the coating process, metal cation electrodeposition onto PPy coating was carried out in 10⁻² M CuCl₂, ZnCl₂, FeCl₂ and NiCl₂ solutions. Corrosion behaviour of uncoated, PPy and PPy|metal coated Cu electrodes was studied in 0.1 M H₂SO₄ solution by using potentiodynamic polarization, chronoamperometric and impedance spectroscopic measurements. Surface morphologies were examined by scanning electron microscope (SEM). All the electrochemical measurements were in good agreement showing that metal electrodeposited PPy coated Cu electrodes have a higher corrosion resistance. Furthermore, SEM results show that while all the samples have a homogeneous distribution of metal cations, zinc and nickel have a much better homogeneous distribution compared to copper and iron. It was found that the best corrosion protection is provided by PPy|Zn and PPy|Ni coatings and there is a significant increase in their polarization resistance with increasing amounts of electrodeposited cations.     

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.     

Benzotriazole as inhibitor for copper with and without corrosion products in aqueous polyethylene glycol

Electrochemical methods, including polarization experiments and impedance spectroscopy, were used to evaluate the effectiveness of benzotriazole (BTA) in an aqueous solution of polyethylene glycol (PEG) in protecting polished archaeological copper or archaeological copper covered with corrosion products. The adsorption of PEG on the polished copper significantly limited the corrosion current. The presence of benzotriazole enhanced the protection of the polished copper, giving maximum protection at a concentration of 10^–2moll^–1 of BTA in 20 vol% PEG 400 solution. On the other hand, PEG solutions caused degradation of the corrosion products of the copper. This degradation increased with time. When BTA was added, the corrosion products were preserved and, the higher the BTA concentration, the more the corrosion current decreased. In PEG 400 solution protection of the corrosion products of the copper by BTA improved over time.     

pH-dependent anodic reaction behavior of tungsten in acidic phosphate solutions

Potentiodynamic and potentiostatic polarization experiments, and the electrochemical impedance spectroscopy technique were used to study the pH dependent anodic behavior of tungsten (W) in acidic phosphate solution. At very low pH values (pH < 2.6) the dissolution of tungsten was H⁺-assisted and as the pzc (pH 2.6) was approached H₂O-assisted dissolution became main dissolution pathway. Above pH 2.6, however, tungsten dissolution was OH⁻-assisted. The thickness and dielectric properties of the W-oxide barrier layer were observed almost pH independent at corrosion potential. The oxygen vacancy transport across the oxide film caused a capacitive response at very acidic solutions (pH ≤ 3.5) and as the dissolution rate increased (pH > 4.5) the capacitive response turned into the inductive one due to the accelerating effect of negative surface charge in Tafel region. The inductive response in the tungsten impedance spectra shifted to a very low frequency range as the tungsten dissolution rate decreased in the pseudo-plateau and potential independent regions. Fitting of the tungsten impedance data according to the surface charge approach showed that the resistance to the defect migration increased as the pzc was approached and the film capacitance decreased above pH 3.5 due to the accelerated formation rate of the non-protective loosely bound hydrated layer on the metal oxide surface.     

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.     

Influence of 8-aminoquinoline on the corrosion behaviour of copper in 0.1 M NaCl

The corrosion behaviour of copper in aerated 0.1 M NaCl solution in presence of 8-aminoquinoline (8-AQ), using open circuit potential (OCP) measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and atomic force microscopy (AFM), was studied. The measurements revealed that the effect of 8-AQ is dependent on its concentration. For concentrations up to 10⁻³ M, the organic compound displaces the corrosion potential following no trend and also reduces the anodic current. In contrast, for concentrations higher than 10⁻³, 8-AQ reduces markedly both, the anodic and cathodic currents and consequently, the corrosion current density of copper. After 9 days of exposure in chloride solution, containing the organic compound, potentiodynamic polarization analyses showed a significant reduction in the anodic response and a less significant reduction in the cathodic response, which is associated with a film formed at the copper surface of about 10 μm in thickness and visually observed by a colour change of the copper surface.In order to elucidate the most likely interaction between the 8-AQ molecule and the different molecular structures probably present on copper surfaces in chloride solutions, some results obtained from theoretical calculations are presented. The following molecular structures were considered: CuCl molecule, CuCl₂⁻ complex, and little copper clusters defect representation built as five atoms on C_4v symmetry. Thus, based on the geometric, energetic, frontier orbital, and Total Electronic Density analysis done for the optimized states found for the systems investigated, we suggest that the most probable interaction of 8-AQ proceeds above CuCl units and free copper sites.     

The electrochemical synthesis of polypyrrole at a copper electrode: corrosion protection properties

Pyrrole was successfully electropolymerized at a copper electrode in a near neutral sodium oxalate solution to generate a homogeneous and adherent polypyrrole film. The growth of these films was facilitated by the initial oxidation of the copper electrode in the oxalate solution to generate a copper oxalate pseudo-passive layer. This layer was sufficiently protective to inhibit further dissolution of the copper electrode and sufficiently conductive to enable the electropolymerization of pyrrole at the interface, and the generation of an adherent polypyrrole film. These films remained stable and conducting for periods exceeding eight days and exhibited significant corrosion protection properties in acidified and neutral 0.1 mol dm⁻³ NaCl solutions even on polarization to high anodic potentials.     

Electrochemical properties of boron-carbon-nitride films formed by magnetron sputtering

The electrochemical behavior of B_1.0C_2.4N_1.0 thin film was investigated in acidic, neutral and alkaline solutions. The anodic polarization curve of the film in 1 M NaOH showed the anodic dissolution of the film. The curve of the film in 1 M HCl showed no anodic dissolution. The cathodic polarization curve in 1 M NaCl showed shift to a negative potential side, but the anodic polarization curve was the same as that of Pt. The anodic dissolution in 1 M NaOH depended on potentials, that is, no anodic dissolution was recognized in a potential range of −0.2 to 0.1 V but the dissolution rate increased with increasing potential in a range of 0.1-0.6 V. The anodic current density of the film is directly proportional to the dissolution rate at potentials higher than 0.1 V. The dissolution rate of the film was increased with increasing solution pH.     

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.     

Atomic emission spectroelectrochemistry applied to dealloying phenomena II. Selective dissolution of iron and chromium during active-passive cycles of an austenitic stainless steel

Atomic emission spectroelectrochemistry was used to investigate selective dissolution of a 304 austenitic stainless steel sample in 2 M H₂SO₄. The partial dissolution rates of Fe, Cr, Ni, Mn, Mo, and Cu were measured as function of time during a series of potentiostatic triggered activation/passivation cycles. When first exposed to sulfuric acid solution, the steel sample was in a passive state with a total steady state ionic dissolution rate expressed as an equivalent current density of 10 μA cm⁻². A transition into the active and passive state could be triggered by cathodic (−700 mV vs. Ag/AgCl) and anodic (+400 to +700 mV vs. Ag/AgCl) potentiostatic pulses respectively of variable time. Excess Cr dissolution was observed during the activation cycle as compared to Fe and a depletion of Cr dissolution was observed during the passivation cycle. These results are interpreted in terms of the dissolution of a Cr rich passive layer during activation and selective dissolution of Fe, Mn, Ni and other elements to form a Cr rich passive layer during passivation. Quantitative analysis of the excess Cr showed that the residual film contained approximately 0.38 μg Cr/cm². Fe does not appear to be incorporated into the film at this early stage of passive film growth. Residual films of metallic nickel and copper were formed on the surface during the active period that subsequently dissolved during passivation.     

Sweet aqueous solution for electrochemical synthesis of polypyrrole part 1B: On copper and its alloys

The electrochemical synthesis of polypyrrole (PPy) on copper and brass has been successfully achieved in sodium saccharinate and pyrrole aqueous medium. The synthesized coating under several electrochemical techniques such as cyclic voltammetry, galvanostatic and potentiostatic is homogeneous and adherent. PPy has been characterized by SEM, XPS, IR and Raman spectroscopy and its quality has been confirmed. The doping level obtained from N 1s XPS signal of the oxidized PPy depends on the electrochemical technique used to produce the film. The corrosion performance of PPy/copper and PPy/brass has been evaluated in 3% NaCl and 0.1 M HCl using linear polarization and electrochemical impedance spectroscopy. The results show that PPy coating electrodeposited from sodium saccharinate exhibits significant corrosion protection properties.     

Influence of water content on nanotubular anodic titania formed in fluoride/glycerol electrolytes

A study has been carried out of nanotubular anodic films formed on titanium at 20 V in fluoride/glycerol electrolyte, containing up to 50 vol.% water. Anodizing was terminated at a charge of 1 C cm⁻². Addition of water resulted in an increased current and significantly reduced tube length associated with increased oxygen gas evolution. Films formed in the absence of added water were amorphous by electron diffraction, whereas water addition also led to the formation of anatase and rutile. The barrier layer was relatively thin for electrolyte of low water content, due to either a voltage drop in the electrolyte close to the anode or to a change in the film composition affecting the electric field across the layer. Ribbing of the external walls of the nanotubes was more evident in the presence of water. It is suggested that dissolution of a fluoride-rich layer, which separates the nanotubes, accompanies the nanotube growth, with the dissolution allowing transient film formation at the external walls of the nanotubes when the residual layer is sufficiently thin.     

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10⁹ Ω cm², whereas that for pure ER coating fell below 10⁶ Ω cm² after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h.     

The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys

An electrochemical approach to the formation of a protective surface film on Mg alloys immersed in the ionic liquid (IL), trihexyl(tetradecyl)phosphonium-bis 2,4,4-trimethylpentylphosphinate, was investigated in this work. Initially, cyclic voltammetry was used with the Mg alloy being cycled from OCP to more anodic potentials. EIS data indicate that, under these circumstances, an optimum level of protection was achieved at intermediate potentials (e.g., 0 or 0.25 V versus Ag/AgCl). In the second part of this paper, a small constant bias was applied to the Mg alloy immersed in the IL for extended periods using a novel cell design. This electrochemical cell allowed us to monitor in situ surface film formation on the metal surface as well as the subsequent corrosion behaviour of the metal in a corrosive medium. This apparatus was used to investigate the evolution of the surface film on an AZ31 magnesium alloy under a potential bias (between ±100 mV versus open circuit) applied for over 24 h, and the film evolution was monitored using electrochemical impedance spectroscopy (EIS). A film resistance was determined from the EIS data and it was shown that this increased substantially during the first few hours (independent of the bias potential used) with a subsequent decrease upon longer exposure of the surface to the IL. Preliminary characterization of the film formed on the Mg alloy surface using ToF-SIMS indicates that a multilayer surface exists with a phosphorous rich outer layer and a native oxide/hydroxide film underlying this. The corrosion performance of a treated AZ31 specimen when exposed to 0.1 M NaCl aqueous solution showed considerable improvement, consistent with electrochemical data.