Corrosion protection of steel by polyaniline blended coating

Phosphate doped polyaniline was synthesized from aqueous phosphoric acid containing aniline by chemical oxidation method using ammonium persulphate as oxidant. The polymer was characterized by UV–vis and FT-IR spectroscopic techniques. Using this polymer, a paint with 1% polyaniline was prepared with epoxy binder. The corrosion resistant property of the polymer containing coating on steel was found out by open circuit potential measurements and electrochemical impedance spectroscopic method in 0.1 N HCl, 0.1 N H₃PO₄ and 3% NaCl for a duration of 50 days. The coating was able to protect the steel more in 0.1 N H₃PO₄ and 3% NaCl media than in 0.1 N HCl.     

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

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 (0.2 M) as a monomer and ammonium persulfate (0.2 M) as an oxidant. The polymer powder produced was changed into emeraldine base (EB) form after treatment with dilute ammonia solution (0.5 M) 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).     

High performance polyaniline containing coating system for wet surfaces

Application of paint coatings on wet surfaces is rather difficult due to poor adhesion of coatings. For painting of wet surfaces, moisture curable coating systems based on epoxy resin and ketimine are found to be useful. Hence a study has been made on the corrosion protection ability of coating on wet surfaces using epoxy resin, ketimine and polyaniline. Paints with 20–30% PVC were prepared and applied over the wet steel surface and the corrosion protection performance of the coating was found out by salt spray and electrochemical impedance spectroscopic techniques. Coating with 20% PVC is found to offer very high protection since the impedance values are remained at greater than 10⁹ Ω cm² after immersion and salt spray tests.     

Corrosion protection of galvanized iron by polyaniline containing wash primer coating

Wash primer treatment of galvanized iron (GI) structure is widely used before painting in order to improve adhesion. Traditional wash primer contains zinc tetroxy chromate. Due to hazardous nature of chromate, alternate compounds for chromate replacements have been identified. In recent years polyaniline containing coating has been found to protect GI. In this study, a wash primer based on polyaniline has been formulated and its corrosion protection ability of GI has been compared with that of traditional chromate based wash primer by salt spray and EIS test. It has been found that the polyaniline based wash primer is able to protect GI and its corrosion protection performance is similar to chromate based wash primer coating.     

Corrosion protection of steel by polyaniline (PANI) pigmented paint coating

The corrosion performance of polyaniline (PANI) pigmented coating on steel has been studied by electrochemical impedance spectroscopy (EIS) in 3% NaCl and 0.1N HCl solutions. Initially, the impedance values were found to decrease due to the corrosion of steel in pin holes of the coating. However, on increased exposure time, the impedance values were found to increase due to the formation of passive film on the exposed steel in pin holes. These studies have shown that the polyaniline pigmented coatings are able to protect the steel both in acid and neutral media.     

Performance evaluation of polyaniline pigmented epoxy coating for corrosion protection of steel in concrete environment

Corrosion protection of mild steel reinforcement offered by a newly developed epoxy based coating system containing inherently conducting polyaniline as one of the pigments has been studied. The synthesis of polyaniline and preparation of epoxy based coating system containing this polyaniline are described here. The corrosion resistant property of epoxy polyaniline system, coated on mild steel was evaluated by various techniques such as electrochemical impedance spectroscopy, potential time studies, cathodic disbondment test, anodic polarization study, salt spray test and chemical resistance test. The corrosion resistance of epoxy polyaniline coating system coated on reinforcement bars embedded in concrete was also studied by an accelerated time to cracking study. The formation of polyaniline was characterized using FTIR, UV, GPC, particle size analyzer and fineness studies. Electrochemical impedance studies reveal that the resistance of the coating decreased initially and then increased due to passivating ability of the polyaniline pigment. Based on the results of different techniques, it is found that epoxy coating with polyaniline pigment is effective in corrosion protection of steel in concrete environment.     

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.     

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.     

In situ electrochemical preparation of multi-walled carbon nanotubes/polyaniline composite on the stainless steel

Polyaniline–carbon nanotubes (PANI–CNTs) composites have been deposited via in situ electropolymerization on stainless steel (SS) surface. The presence of the oxidized multi-walled carbon nanotubes (mCNTs) in the composite was confirmed by thermal gravimetric analysis (TGA) and scanning electron microscope. Introducing 28 and 70 mg L⁻¹ mCNT in the electrolyte increased the growth rate of PANI from 38 to 67 and 83 mC/cycle, respectively. The mCNT decreases the porosity of the PANI, forming networks which held the polymer. Influences of the composite layer on the passivation and corrosion of the stainless steel were studied and compared with pure PANI layer. It was confirmed that a higher resistant passive film was formed on the steel under the composite layer compared to that formed under the pure PANI.     

Corrosion protection of new composite polymer coating for carbon steel in sulfuric acid medium by electrochemical methods

In this paper, electropolymerization technique has been used for the obtained of new composite: polypyrrole – dioctyl sulfosuccinate sodium/poly N-ethylaniline (PPY-AOT/PNEA) coatings over carbon steel of type OLC 45 electrode for anticorrosion protection. The PPY-AOT/PNEA coatings were successfully synthesized onto OLC 45 electrode by galvanostatic deposition from aqueous solutions 0.1 M NEA, 0.1 M PY, 0.01 M AOT and 0.3 M H₂C₂O₄ solution at different current densities (5, 3 and 1 mA/cm²) in different molar ratio. The anionic surfactant (AOT) as a dopant ion used during electropolymerization can have a significant result on the anticorrosion protection of the composite film by hindering the penetration of aggressive ions. The polymeric composite coatings have been analyzed by cyclic voltammetry (CV), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) methods. The corrosion resistance of PPY-AOT/PNEA coated carbon steel has been examined by potentiodynamic polarization techniques and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solutions. The data of the corrosion samples demonstrated that PPY-AOT/PNEA coatings assure a great anticorrosion protection of OLC 45 electrode in corrosive media. The corrosion rate of PPY-AOT/PNEA coated OLC 45 has been indicated to be ~9 times lower than of uncoated electrode. The corrosion protection effectiveness of the composite coating is more than 89%. The best efficiency is accomplished of PPY-AOT/PNEA obtained by electrodeposition at 5 mA/cm² current densities applied in molar ratio 5:1.     

A new corrosion protection coating with polyaniline-TiO2 composite for steel

Organic coating strategies for corrosion protection with inherently conducting polymers have become important because of restriction on the use of heavy metals and chromates in coatings due to their environmental problems. This work presents the synthesis of polyaniline-TiO₂ composites (PTC) and the corrosion protection behaviour of PTC containing coating on steel. PTC was prepared by chemical oxidation of aniline and TiO₂ by ammonium persulfate in phosphoric acid medium. The PTC was characterized by FTIR, XRD and SEM techniques. Suitable coating with PTC was formed on steel using acrylic resin. Using electrochemical impedance spectroscopy, the PTC containing coating's behaviour in 3% NaCl immersion test and salt spray test has been found out. Results indicate that the coating containing PTC is able to maintain the potential of steel in passive region due to its redox property. The resistance of the coating containing PTC was more than 10⁷ Ω cm² in 3% NaCl solution after 60 days and 10⁹ Ω cm² in the salt spray test of 35 days. But the resistance of the TiO₂ containing coating was found to be less than 10⁴ Ω cm² in both the cases. The high performance of PTC containing coating is attributed to the passivation of steel by polyaniline.     

Corrosion of mild steel with composite polyaniline coatings using different formulations

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

Nanosilicon dioxide/o-phenylenediamine hybrid composite as a modifier for steel paints

Different amounts of the hybrid composite nano SiO₂/o-phenylenediamine were added to a typical paint being used for protecting steel against corrosion to increase its protection efficiency. The nano features of the composite were confirmed by different electron microscopic investigations. It was found that the protection efficiency of the paint increased significantly as well as its adhesion to the steel surface increased. These conclusions had been inferred from both potentiodynamic polarization and electrochemical impedance spectroscopy techniques. To confirm the previous concept salt spray test and adhesion force measurements were carried out. The results were interpreted in terms of the filling properties of nano SiO₂ and adsorption/hardening power of o-phenylenediamine.     

Performance of polyaniline pigmented vinyl acrylic coating on steel in aqueous solutions

Using electrochemical impedance spectroscopy method, the performance of vinyl acrylic coating containing polyaniline on steel in 0.1 N HCl, 3% NaCl and cement extract (pH 13.0) has been evaluated. The resistance of the paint coating in all the media has been found to decrease initially from 10⁸ to 10⁶ Ω cm². On subsequent exposure to the aqueous media, the resistance of the coating has been found to increase steadily. Further, the open circuit potential values have been found to shift in active direction initially and then move in noble direction with longer immersion period due to the passivating effect of polyaniline pigment.     

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.     

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.     

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.     

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.     

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.     

Resistance of metallic substrates protected by an organic coating containing glass flakes

The resistance against corrosion of an epoxy-polyamine-based coating immersed in a 3 wt.% sodium chloride solution was investigated by electrochemical impedance spectroscopy (EIS). The organic coating contained glass flakes as pigment in order to enhance its barrier characteristics. The data show that this coating is more strongly adhered and exhibits higher protection characteristics when applied onto carbon steel substrates than on galvanized steel. Though the capacitance of the coating (C_C) does not show any appreciable variation with immersion time, the resistance (R_PO) of the film is observed to increase with time upon immersion. The analysis of the data sustains that the organic film behaves as a porous, non-barrier coating. Two time constants are observed even at earlier exposures, and the improved corrosion resistance developed after the coating system was exposed to the test electrolyte is considered to originate from the precipitation of corrosion products within the pores in the film.