Electropolymerised polyaniline films on AA 7075 alloy and its corrosion protection performance

Polyaniline has been electrodeposited on AA 7075 alloy and its corrosion protection ability has been studied by Tafel and impedance techniques in 1% NaCl. Pure polyaniline film is not found to protect the aluminium alloy due to galvanic interaction of polyaniline and aluminium surface exposed through pinholes and cracks. However, it is found that the corrosion resistance property of the polyaniline film can be substantially increased by post-treatment in cerium salt solution.     

Electropolymerized bilayer coatings of polyaniline and poly(N-methylaniline) on mild steel and their corrosion protection performance

Polyaniline (PANI) and poly(N-methylaniline) (PNMA) have been electrodeposited on mild steel from oxalic acid bath using cyclic voltammetric technique. Pretreatments like passivation and primer polymer coatings were required for effective coating. Differently stacked composite polymer layers on the metal surface by layer-by-layer approach have also been obtained and their properties have been compared with their corresponding copolymer coatings. FTIR study confirms the formation of electroactive polymer compounds on mild steel. Evaluation of these coatings in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy reveals significant corrosion resistant behavior. Relatively higher corrosion protection is exhibited by copolymer coatings and composite-bilayer coatings than the corresponding homopolymer coatings. The composite metal–PANI–PNMA layer shows higher stability and better protection than the metal–PNMA–PANI layer.     

High corrosion protection of a polyaniline/organophilic montmorillonite coating for magnesium alloys

Epoxy coatings containing polyaniline (PANI) and polyaniline/organophilic montmorillonite (PANI/OMMT) powders were prepared on the surface of AZ91D magnesium alloy. The corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and open-circuit potential analysis in 3.5% NaCl. The results indicate that the PANI/OMMT coating retained its high corrosion protection for AZ91D magnesium alloy after 6000 h of immersion. The protective mechanism conferred by the PANI/OMMT coating was also discussed. The effects of oxygen on the protective mechanism of PANI were evaluated by EIS measurements in a 3.5% deaerated NaCl solution.     

Epoxy powder coatings containing polyaniline for enhanced corrosion protection

Incorporation of polyaniline (PANI) in epoxy type powder coating formulations has not been attempted earlier. Using specific grade of PANI with low doping, it can be incorporated in epoxy powder coating formulations by twin screw extrusion process. The powder formulations were deposited on steel substrates by electrostatic spray coating at −60 kV and baked at 140 °C for 20 min. These were extensively tested for corrosion resistance by exposure to hot saline conditions followed by electrochemical impedance spectroscopy and also salt spray testing. PANI incorporated coatings showed no deterioration even after 1400 h of hot (65 °C) saline treatment. The coatings intentionally scratched also exhibited self healing property and there was no rust formation even after prolonged exposure to hot saline conditions. These results could be explained on the basis of additional crosslinking due to PANI, as confirmed by DSC results, which gave rise to improved barrier property and self healing was associated with the scavenging of ions by PANI which prevented corrosion of the underlying substrate.     

Corrosion protection of iron by benzoate doped polyaniline containing coatings

Polyaniline containing organic coatings based on vinyl and acrylic resins are found to protect iron in acid and neutral media. Since dopants play an important role in forming salts with iron, a study has been made on the effect of benzoate doped polyaniline on the corrosion protection of iron by polyaniline–vinyl coatings in acid and neutral media. EIS studies have been made on the corrosion protection performance of vinyl coating on steel with 1% polyaniline in 0.1N HCl and 3% NaCl up to 100 days of exposure. It has been found that benzoate doped polyaniline containing coating has found to offer more protection in neutral media than that in acidic media due to passivating ability of benzoate ions in neutral solution, along with iron–polyaniline complex.     

Effective corrosion protection of AA6061 aluminum alloy by sputtered Al-Ce coatings

Al-Ce coatings were deposited on silicon and AA6061 aluminum alloy substrates by DC magnetron sputtering using aluminum in combination with pure cerium targets. The materials were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electrochemical impedance spectroscopy (EIS) in order to consider their application as high corrosion resistance coatings. The corrosion behavior of the films was studied using a NaCl aqueous solution (3.5 wt%). As for the characterization results, an apparent amorphous phase of aluminum oxide with small cerium compounds embedded in the matrix was detected by the X-ray diffraction patterns and HRTEM on the deposited films at 200 W and 4 Pa. At these conditions, AFM and SEM images evidenced crack-free coatings with low-roughness nanometric structures and columnar growth. EIS and Tafel results converged to indicate an inhibition of the corrosion reactions. The film displayed good stability in the aggressive medium and after 1 day of exposure underwent very little degradation. The variations in the impedance and Tafel characteristics were found to occur as a function of cerium content, which provokes important changes in the film protective properties.     

Investigation of corrosion protection performance of epoxy coatings modified by polyaniline/clay nanocomposites on steel surfaces

In this study, polyaniline (PANI) and polyaniline/clay nanocomposites were prepared via in situ oxidative polymerization. The morphology of nanocomposites structures was investigated by X-ray diffraction (XRD). The chemical structures of PANI and PANI/clay nanocomposites were examined via Fourier transform infrared (FT-IR) spectroscopy. Polyaniline-based pigments were introduced into epoxy paint and applied on steel substrates. The effect of clay addition and the type of clay cation, including Na⁺ in natural clay (MMT) and alkyl ammonium ions in organo-modified montmorillonite (OMMT), on the anticorrosion performance of epoxy-based coatings was investigated through electrochemical Tafel test, electrochemical impedance spectroscopy and immersion measurements in NaCl solution. The stability of the adhesion of the neat and modified epoxy coatings to the steel surface was also examined. The results indicated that introduction of PANI/OMMT nanocomposite into epoxy paint results in improved anticorrosion properties in comparison with PANI/MMT and neat PANI.     

Novel hybrid sol-gel coatings for corrosion protection of AZ31B magnesium alloy

This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol-gel coating approach.Hybrid organic-inorganic sols were synthesized by copolymerization of epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol-gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005 M NaCl solution for 2 weeks. The sol-gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg-O-P chemical bonds.The structure and the thickness of the sol-gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol-gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol-gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling.     

The influence of thin benzoate-doped polyaniline coatings on corrosion protection of mild steel in different environments

The corrosion process of mild steel in the presence of benzoate-doped polyaniline coatings exposed to different environments (3% NaCl, atmosphere, and the Sahara sand) has been investigated. This system was also tested for cathodic protection and it has proven more efficient comparing to mild steel alone. Possible mechanisms of the corrosion protection of mild steel in the presence of a polyaniline-based coating in different corrosion media were also proposed.     

Inhibition of nickel coated mild steel corrosion by electrosynthesized polyaniline coatings

Polyaniline (PANI) coatings were electrochemically synthesized on nickel (Ni) coated mild steel (MS) and their corrosion protection properties were investigated. In this work, the Ni layer (∼1 μm thick) was electrodeposited on MS under galvanostatic condition. Thereafter, the PANI coating was deposited over the Ni layer from aqueous salicylate medium by using cyclic voltammetry. These bi-layered composite coatings were characterized by cyclic voltammetry, UV–vis absorption spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The corrosion protection properties of Ni coated MS (Ni/MS) and PANI coated Ni/MS (PANI/Ni/MS) were investigated in aqueous 3% NaCl by using open circuit potential (OCP) measurements, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). It was shown that the top layer of PANI exhibits a lower porosity behavior with respect to Ni coating and reduces the corrosion rate of Ni/MS almost by a factor of 3500 and increases the lifetime of Ni coating.     

Influence of the doping agent on the corrosion protection properties of polypyrrole grown on aluminium alloy 2024-T3

The corrosion protection properties of polypyrrole (PPy) electrodeposited onto aluminium alloy 2024-T3 substrates were investigated as a function of the doping agent. We used camphor sulfonic acid (CSA), para toluene sulfonic acid (p-TSA), phenylphosphonic acid (PPA), oxalic acid (OA) and cerium nitrate salt (Ce(NO₃)₃) as doping agents. The resulting coatings have been evaluated towards corrosion protection of aluminium alloy 2024-T3 using electrochemical impedance spectroscopy (EIS). Complementary, scanning electron microscopy (SEM) provided images on the morphology and the thickness of the coatings. The results showed that coatings formed using Ce(NO₃)₃ solution protect the substrate more efficiently compared to the other coatings.     

Electrosynthesis of polyaniline–molybdate coating on steel and its corrosion protection performance

Electrosynthesis of polyaniline–molybdate (PANI–MoO₄²⁻) on mild steel was achieved in oxalic acid medium using cyclic voltammetry technique. Adherent and homogeneous PANI–MoO₄²⁻ coating was obtained. The corrosion behavior of steel with PANI–MoO₄²⁻ coatings in 1% NaCl solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The coating was characterized by SEM, XPS, EDAX and FTIR. The self-healing ability of PANI–MoO₄²⁻ coating was confirmed by SVET technique. It has been found that the PANI–MoO₄²⁻ coating is able to offer higher corrosion protection in comparison to that of pure PANI coating due to inhibitive nature of molybdate ions.     

Polyaniline coatings on aluminium alloy 6061-T6: Electrosynthesis and characterization

The production of polyaniline films on aluminium alloy 6061-T6 in sulphuric acid was carried out by electrodeposition, using cyclic voltammetry and potentiostatic polarization. The films obtained were characterized by SEM and XPS analysis. Electrochemical techniques were also used to assess the anticorrosive properties of the coatings.The choice of the upper potential limits for potential cycling and of the fixed potential for potentiostatic production should take in consideration the balance between their effect on the minimum number of cycles (or time) needed to produce the film and on the rate of overoxidation.Polarization curves show a slight increase of the corrosion potential for polyaniline coated substrate as compared with bare metal, indicating that no significant protection is achieved by the polymer coating. The Bode diagrams show low impedance values for the alloy covered with polyaniline when compared with the results obtained for the bare metal. This can be attributed to the conductive character of the polyaniline films.     

Corrosion protection of magnesium ZM 21 alloy with polyaniline–TiO2 composite containing coatings

A polyaniline–TiO₂ composite (PTC) was prepared by oxidative polymerization of aniline in phosphoric acid with ammonium persulphate, in the presence of TiO₂. The composite was characterized by spectroscopic methods. An acrylic paint containing the PTC was prepared and the coating formed on magnesium alloy was evaluated by electrochemical impedance spectroscopy after exposure to salt spray test for a period of 250 h. The coating containing the PTC was found to protect the magnesium alloy more efficiently than the coating containing polyaniline.     

Organic coatings containing polyaniline and inorganic pigments as corrosion inhibitors

Polyaniline (PANI) was synthesized by chemical oxidative polymerization in laboratory conditions. The main objective was to study the properties of organic coatings containing PANI and PANI in combination with other anti-corrosive pigments. The adhesion, barrier, and anti-corrosion properties of the coatings containing PANI and selected chemically active pigments were studied as well as the combination of PANI with zinc dust. Epoxy resin of bisphenol type hardened with a polyamine-based curing agent was used as a binder. In order to examine the synergic effect of PANI and anti-corrosion pigment in epoxy coatings, Zn₃(PO₄)₂·2H₂O with an acidic aqueous extract, Ca₃(BO₃)₂ with a basic aqueous extract and SrCrO₄ with a neutral aqueous extract have been tested.     

Sol-gel coatings for corrosion protection of 1050 aluminium alloy

The formation of organic-modified sol-gel coatings on 1050 aluminium alloy has been examined. The coatings were prepared by the combination of a completely hydrolysable precursor of tetra-n-propoxyzirconium (TPOZ), with a partly hydrolysable precursor of glycidoxypropyltrimethoxysilane (GPTMS). Influences of GPTMS/TPOZ ratio, withdrawal speed and curing temperature on the barrier-type corrosion protection of the alloy were examined. By control of process parameters and ratios of organic and inorganic moieties, crack-free sol-gel coatings with improved corrosion protection were produced on the alloy surface. Optimum protection was achieved by a coating formed with a GPTMS/TPOZ ratio of 2.7, a withdrawal speed of 180 mm/min and curing at 110 °C. The coating formed under the optimum conditions revealed good adhesion to the etched and desmutted alloy substrate. The pitting potential of the coated alloy increased significantly, indicative of an improved corrosion protection of the alloy.     

Influence of inhibitor addition on the corrosion protection performance of sol–gel coatings on AA2024

Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.     

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of polyaniline and polypyrrole

Homopolymers and bilayers of polyaniline (PAni) and polypyrrole (PPy) coatings have been electropolymerized on mild steel by potentiodynamic synthesis technique in aqueous oxalic acid solutions. Characterization of coatings was carried out by cyclic voltammetry. Corrosion behavior of the polymer coated mild steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy (EIS) techniques in various aqueous corrosive solutions. Corrosion test results clearly showed that PPy and PAni/PPy bilayer coatings served as a stable host matrix on mild steel against corrosion. However, bilayers of PAni and PPy did not exhibit good combined properties of each polymer, unlike expected. PPy exhibited the best corrosion resistance among all coatings.     

Effective corrosion protection of 8090 alloy by cerium conversion coatings

Conversion treatments based on immersion in Cr(VI) aqueous solutions are key technologies that combine low cost, easy application and high performance. However, they are environmentally problematic due to their carcinogenity and genotoxicity. Among the potential alternatives, treatments based on rare-earth compounds have drawn attention due to the stability of their oxides and their environmental acceptability. Despite the amount of work published, there is not yet an industrially suitable alternative treatment for aircraft aluminium alloys that is able to provide the required corrosion protection. A common feature of these alloys is the high level of copper in their chemical composition. Although the presence of copper in an alloy may enhance cerium deposition, high copper content alloys (AA2024, AA7075) have proven the most difficult to protect with Ce conversion coatings.In the present work, a commercial 8090-T8 aluminium alloy containing 1.15 weight percent (wt.%) Cu was coated with a Ce conversion coating at room temperature from a Ce bath without prior pretreatment of the specimens. Polarisation curves revealed that the presence of a cerium conversion coating (CeCC) reduces by two orders of magnitude the corrosion rate of the AA8090 alloy in a sodium chloride solution. Impedance measurements exhibited capacitive behaviour for the CeCC up to 216 h, showing that the cerium layer protects the bare alloy in the aggressive solution.Electrochemical tests have therefore revealed that these conversion layers afford long-lasting protection; withstanding up to 168 h in Salt Spray test.     

A review on conducting polymer coatings for corrosion protection

Corrosion of metals is one of the most important problems in the manufacturing industries. Many corrosion control methods use coatings of conducting polymers and conversion layers that contain toxic and environmentally hazardous materials, especially chromium compounds. These objectives have led to the development of new protective coating strategies that employs nanocomposites and carbon-based materials. In recent years, conducting polymers have attracted much attention because of their wide range of industrial applications and economic viability. Polymers possess long-chain carbon linkages and therefore, upon adsorption are able to block large areas of the corroding metal surfaces. The thin films adsorbed on the metal substrate provide a barrier effect between the metal and its environment. This review article summarizes the different techniques used in corrosion protection of metals, conducting polymers and nanomaterials, nanocomposites, and carbon-based materials in corrosion science.