A new smart coating of polyaniline–SiO2 composite for protection of mild steel against corrosion in strong acidic medium

Organic coating approaches 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. The present work is directed towards the synthesis of polyaniline (PANI) and polyaniline–SiO₂ composites (PSCs) by chemical oxidation polymerization in the presence of phosphoric acid and evaluation of synthesized PANI and PSCs for protection of mild steel from corrosion in a strong aggressive medium (i.e. 1.0 mol L^–1 HCl). A suitable coating with PSC was formed on mild steel using epoxy resin by the powder coating technique. A comparative study of the corrosion protection efficiency of mild steel coated with PANI and PSC in 1.0 mol L^–1 HCl solution was evaluated using the Tafel extrapolation, chrono‐amperometry and weight loss methods. The PSC coating showed that a significant reduction in the corrosion current density reflects the better protection of mild steel in an acidic environment. Higher protection efficiency up to 99% was achieved by using PSC‐coated mild steel at 6.0 wt% loading of PSC in epoxy resin. The coating performance and corrosion rate of mild steel were investigated by using immersion of polymer‐coated mild steel in 1.0 mol L^–1 HCl for 60 days and indicated that PSC‐coated mild steel showed better performance from corrosion than PANI in an acidic medium.© 2012 Society of Chemical Industry     

Accelerating effect and mechanism of passivation of polyaniline on ferrous metals

To investigate the corrosion protection mechanism of polyaniline (PANI) films on ferrous metals, this work presents preparation method of a separate protonated PANI film electrode and results of its open-circuit potential (OCP) in 0.5 M NaClO₄ and 0.5 M Na₂SO₄ solutions with different pH and the galvanic interaction between the PANI film electrode and ferrous metals. X-ray photoelectron spectroscopy (XPS) shows the lower pH corresponds to higher protonation level of H⁺ in the film, and a more positive OCP of PANI film. The PANI film accelerated the corrosion of 20A carbon steel slightly with a PANI to steel area ratio less than 25:1, while the PANI films maintained passivity for a ratio above to 25:1 for the 20A steel. For the coupling of 2Cr13 stainless steel/PANI, an equal area PANI film could maintain 2Cr13 in a passive state. The results suggest that corrosion protection of 20A carbon steel and 2Cr13 stainless steel by PANI film in the acid solution is due to passivity protection. The excess oxidative charge stored in the PANI and the equilibrium activity of protonated PANI with the acid environment provide a persistent driving force for carbon steel and 2Cr13 stainless steel passivity.     

Polyaniline Top Coat Modified on Nickel-Plated Mild Steel: AC Impedance Analyzer

Polyaniline (PANI) was synthesized from 0.1 M aniline containing neutral medium such as sodium oxalate. The synthesis was achieved on 1-µm Ni-plated mild steel (MS/Ni) by using cyclic voltammetry technique. The corrosion performances of PANI coating with and without MS/Ni electrodes were evaluated by using AC impedance spectroscopy (EIS) and anodic polarization curves in 3.5% NaCl solution. It was found that Ni plating showed an important barrier property on MS. This case decreased drastically in longer periods, and the porosity values increased in chloride ions medium, which has small ion diameter. In the presence of PANI top coat, the porosity values remained almost constant against the attack of corrosive products for extended periods. It indicated that PANI coating could provide a significant protection property to MS/Ni, by catalyzing the formation of a stable nickel oxide layers with time. The catalytic behavior of polymer film also contributed to improvement of barrier property of PANI coating due to transformation to the reduced structure.     

The influence of polyaniline (PANI) coating on corrosion behaviour of zinc–cobalt coated carbon steel electrode

Zinc–cobalt alloy plating (ZnCo) was successfully deposited on carbon steel (CS) applying current of 2 mA with galvanostatic technique. Polyaniline film (PANI) was synthesized with cyclic voltammetry technique from 0.20 M aniline containing 0.20 M sodium tartrate solution on zinc–cobalt plated carbon steel (CS/ZnCo) electrode. PANI film characterized by scanning electron microscopy (SEM), was covered with a dark green-brown homopolymer film of strongly adherent homogeneous characteristic while the other one was plated with a porous light ZnCo one. The corrosion behaviour of zinc–cobalt deposited carbon steel electrodes with and without polyaniline (PANI) film in 3.5% NaCl solution was investigated with AC impedance spectroscopy (EIS) technique and anodic polarization curves. The results showed that PANI coating led to decrease of the permeability of metallic plating. The PANI homopolymer film provided an effective barrier property on zinc–cobalt coating and a remarkable anodic protection to substrate for longer exposure time.     

Preparation of PANI/epoxy/Zn nanocomposite using Zn nanoparticles and epoxy resin as additives and investigation of its corrosion protection behavior on iron

Conducting polyaniline, zinc and epoxy resin solely have anticorrosive properties by different mechanisms on metallic substrates. In this work the triple hybrid of PANI/epoxy/Zn nanocomposite was prepared as a thin layer coating (70 ± 5 μm) on iron coupons and its anticorrosion performance was investigated in HCl (0.1 M) as corrosive solution. Epoxy resin and zinc nanoparticles were applied as additives in the PANI matrix to improve the mechanical properties of PANI coating and investigate their synergetic effects on the anticorrosion performance of PANI coating. At first PANI/Zn nanocomposite coatings with different Zn contents were prepared and the zinc content optimized so that the coating achieve the best anticorrosion performance. Accordingly the iron coupons coated by PANI/Zn coating having 4 wt% Zn content showed more noble open circuit potential and lower corrosion current values. Then epoxy resin was applied as additive to the optimized formulation of PANI/Zn coating in different weight percents (0–20 wt%) and the anticorrosion performance of the related PANI/epoxy/Zn triple hybrid nanocomposite coatings was evaluated. Results showed that the addition of epoxy resin causes to the decreasing of corrosion current of iron samples coated by PANI/epoxy/Zn nanocomposite. An optimum range of 3–7 wt% was obtained for the epoxy content in the composition of PANI/epoxy/Zn nanocomposite in which the coating exhibits the best anticorrosion performance. Iron metal coupon was elementally analyzed and the PANI/Zn and PANI/epoxy/Zn nanocomposites were characterized using Fourier Transform Infrared spectroscopy, X-ray diffraction patterns and Scanning Electron Microscopy techniques.     

Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Epoxy/polyaniline–ZnO nanorods hybrid nanocomposite coatings: Synthesis,characterization and corrosion protection performance of conducting paints

The objective of this research is the production of an epoxy coating blended with organic–inorganic hybrid nanocomposite as a corrosion inhibiting pigment applied over carbon steel grade ST37. A series of conducting polyaniline (PANI)–ZnO nanocomposites materials has been successfully prepared by an in situ chemical oxidative method of aniline monomers in the presence of ZnO nanorods with camphorsulfonic acid (CSA) and ammonium peroxydisulfate (APS) as surfactant and initiator, respectively. The synthesized polymers were characterized by X-ray diffraction pattern (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and electrical conductivity techniques. Synthesized nanocomposites were solved in tetraethylenpentamine (TEPA), and then prepared solution was mixed with epoxy and then was applied as a protective coating on carbon steel plates. The anti-corrosion behavior of the epoxy binder blended with PANI–ZnO nanocomposites were studied in 3.5% NaCl solution at a temperature of 25 °C by electrochemical techniques including electrochemical impedance spectroscopy (EIS) and chronopotentiometry at open circuit potential (OCP). It was observed that the epoxy coating containing conducting PANI–ZnO nanocomposites exhibited higher corrosion resistance and provided better barrier properties in the paint film in comparison with pure epoxy and epoxy/PANI coatings. In the case of conducting coatings, the OCP was shifted to the noble region due to presence of PANI pigments. Additionally, the possibility of formation of a passive film in the presence of PANI was reinforced at the substrate–coating interface. SEM studies taken from surface of the coatings showed that epoxy/PANI–ZnO hybrid nanocomposite coating systems (EPZ) are crack free, uniform and compact. Furthermore, it was found that the presence of ZnO nanorods beside PANI can significantly improve the barrier and corrosion protection performance of the epoxy coating due to the flaky shaped structure of the PANI–ZnO nanocomposites.     

Synthesis and characterization of poly(aniline) and poly(o-anisidine) films in sulphamic acid solution and their anticorrosion properties

Poly(o-anisidine) (POA) and polyaniline (PANI) coatings were synthesized on platinum (Pt) surface and stainless steel (SS) in monomer containing 0.50 M sulphamic acid (SA) solution by means of cyclic voltammetry (CV) technique. Meanwhile, poly(o-anisidine) film was also deposited with a different scan rate on SS electrode. The behaviour of PANI and POA films obtained on stainless steel examined by CV was different from the one obtained for PANI and POA on Pt electrode. The corrosion performances of PANI and POA coatings in 3.5% NaCl solution were investigated with anodic polarization technique and electrochemical impedance spectroscopy (EIS). EIS measurements verified the effect of monomers and that of scan rate on corrosion inhibition of coatings on SS electrode. The results showed that POA film synthesized at low scan rate exhibited an effective anticorrosive property on SS electrode. POA synthesized at low scan rate and PANI coatings provided a remarkable anodic protection to SS substrate for longer exposure time than the one observed for POA coating produced at high scan rate as well as that of bare SS electrode.     

Protection of type 430 stainless steel against pitting corrosion by ladder conductive polymer

Poly(o-phenylenediamine) (PoPD) was electropolymerized by cyclic voltammetry (CV) on 430 stainless steel from sulfuric acid solution containing o-phenylenediamine monomer. The formation of the polymer film is slower than that of polyaniline (PANI) film. Transparent and compact layers (∼1.0 μm) of PoPD deposited after 100 cycles, while thicker (∼3 μm), grainy and porous layers of PANI formed after 50 cycles. The PoPD layers protect the steel substrate from pitting in 3% NaCl but the layers of PANI fail, and pitting and crevice corrosion were observed on the steel surface. Both polymers keep the steel substrate in a passive state in sulfuric acid. After aging in acid solution the underlying oxides were investigated after peeling off the polymer layers; this showed an excellent passive film formed under PoPD. The passive steel was completely free from pitting after immersion in the chloride solution for 1 week.     

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.     

Corrosion protection of mild steel by nano-colloidal polyaniline/nanodiamond composite coating in NaCl solution

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was synthesized on mild steel via electrochemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. X-ray diffraction and FTIR techniques confirmed the intercalation of the nanoparticles in PANI matrix. The corrosion performance of the coatings was investigated in 3.5% NaCl solution by electrochemical impedance spectroscopy (EIS), polarization, and salt spray methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in corrosive medium. EIS and polarization measurements indicated that the coating resistance and corrosion resistance values for the PANI/ND nanocomposite coating were much higher than that of pure PANI-coated electrode. Also, the results obtained revealed that the protection efficiency of PANI/ND-coated mild steel is achieved about 90% after 3 days. The porosity in PANI/ND nanocomposite coating is almost 18 times lower than that of the PANI coating.     

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.     

A passivation mechanism of doped polyaniline on 410 stainless steel in deaerated H2SO4 solution

To investigate the role of polyaniline (PANI) in the corrosion protection of stainless steel (SS) in oxygen-deficient acidic solution, a separate doped PANI film electrode on a glass substrate was prepared and the test solution (1 M H₂SO₄) was purged with high-purity N₂ until dissolved oxygen level decreased more than two orders of magnitude. In this deaerated 1 M H₂SO₄ solution, the galvanic coupling interaction between the separate PANI film electrode and 410 SS was studied. Results reveal that the separate PANI film can passivate the 410 SS steadily for a long period of time. A variety of experimental methods including potentiodynamic measurement, potentiostatic (current-time) examination and X-ray photoelectron spectroscopy (XPS) are used to explore the mechanism by which the separate PANI film passivated the galvanic coupling SS in the deaerated sulfuric solution. These studies show that passivation is achieved because PANI film provides a large critical current at the early stage of coupling and a persistent passive current by its electrochemical dedoping/re-doping equilibrium activity with the acidic environment at the subsequent stage of coupling.     

Electrochemical deposition and characterization of ZnCo alloys and corrosion protection by electrodeposited epoxy coating on ZnCo alloy

ZnCo alloys electrochemically deposited on steel under various deposition conditions were investigated. The influence of deposition current density, temperature and composition of deposition solution on the phase structure and corrosion properties of ZnCo alloys were studied. It was found that ZnCo alloy obtained from chloride solution at 5 A dm⁻² showed the best corrosion properties, so this alloy was chosen for further examination. Epoxy coating was electrodeposited on steel and steel modified by ZnCo alloy using constant voltage method. The effect of ZnCo alloy on the corrosion behavior of the protective system based on epoxy coating is interpreted in terms of electrochemical and transport properties, as well as of thermal stability.     

Preparation of Tung Oil-Loaded PU/PANI Microcapsules and Synergetic Anti-Corrosion Properties of Self-Healing Epoxy Coatings

Tung oil is used as a catalyst-free repair agent. Tung oil-loaded polyurethane (PU) microcapsules are prepared by interfacial polymerization in a SiO₂-stabilized Pickering emulsion system, polyaniline (PANI) is deposited in situ on the PU microcapsule surface, and tung oil-loaded PU/PANI double-layer shell microcapsules are obtained. Synthesized PU/PANI microcapsules showed the characteristic dark-green color of conductive PANI. The average particle size is 31.1 ± 8.1 µm and the core content is 45.1 ± 4.3 wt%. The microcapsules have a good thermal stability, and the chemical structure of the PU/PANI wall and tung oil core is confirmed by Fourier transform infrared analysis. Self-healing anti-corrosion coatings are prepared by adding 10 wt% microcapsules into epoxy resin. The corrosion resistance properties of the self-healing coating are evaluated by immersing scratched coatings in 10 wt% NaCl solution for 15 days. The self-healing coating with 10 wt% tung oil-loaded PU/PANI microcapsules have the best anti-corrosion property, and slight corrosion do not occur until 15 days after immersion in salt solution. The self-healing and anti-corrosion mechanism are revealed. The tung oil core and the PANI wall of microcapsules contributed synergistically to the excellent self-healing and anti-corrosion properties of the coating through the formation of self-healing films and passivation layers.     

Preparation of Poly(<Emphasis Type="Italic">o</Emphasis>-toluidine)/Nano Zirconium Dioxide (ZrO<Subscript>2</Subscript>)/Epoxy Composite Coating and Its Corrosion Resistance

Conducting polymers represent a promising application prospect in the field of metal corrosion control. In this investigation, poly(o-toluidine) (POT)/nano zirconium dioxide (ZrO₂) composite were prepared by in situ polymerization of o-toluidine monomer in the presence of nano ZrO₂ particles. Fourier transformation infrared spectroscopy, UV–visible spectroscopy, X-ray diffraction and Scanning electron microscopy were used to characterize the composition and the structure of the composite. POT/nano ZrO₂ composite was mixed with epoxy resin (EP) through a solution blending method and the three components POT/nano ZrO₂/epoxy composite coating was coated onto the surface of steel coupon, and its corrosion protective efficiency was studied by electrochemical measurements and immersion test in 3.5 % NaCl solution as corrosion environment and also compared with that of POT/epoxy composite coated steel, polyaniline (PANI)/epoxy composite coated steel and pure epoxy coated steel. According to the results, POT/nano ZrO₂/epoxy composite coated steel has got higher corrosion resistance than that of POT/epoxy composite coated steel and PANI/epoxy composite coated steel. It was found that POT powders dispersed in the epoxy and polyamide system improved the barrier and electrochemical protection properties of epoxy coating and the addition of nano ZrO₂ particles increased the tortuosity of the diffusion pathway of corrosion substances.     

Preparation and anticorrosive properties of PANI/Na-MMT and PANI/O-MMT nanocomposites

Nanocomposites of polyaniline (PANI) with organophilic montmorillonite (O-MMT) and hydrophilic montmorillonite (Na-MMT) were prepared. The nanocomposites were characterized using FT-IR, D.C. electrical conductivity measurement and cyclic voltammetry techniques. It was found that PANI/Na-MMT nanocomposite has lower (5.8%) and PANI/O-MMT nanocomposite has higher (29.4%) conductivity compared to pure polyaniline. Cyclic voltammetry experiments showed that both nanocomposites are electroactive. The anticorrosive properties of a 100 μm thickness coating of nanocomposites on iron coupons were evaluated and compared with pure polyaniline coating. According to the results PANI/MMT nanocomposites have enhanced corrosion protection effect in comparison to pure polyaniline coating. Results showed also that the PANI/Na-MMT and PANI/O-MMT nanocomposites have considerably different corrosion protection efficiencies in various corrosive environments.     

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%.     

Epoxy curing by polyaniline (PANI) – Characterization and self-healing evaluation

Polyaniline (PANI) was synthesized by chemical oxidative polymerization of aniline dissolved in aqueous phosphoric acid. The polymer was characterized by UV–Visible spectroscopy (UV–Vis), thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopic (FTIR) techniques. Hardener free epoxy coating was formulated with 10% PANI. The curing process of epoxy resin by PANI was analyzed using FTIR and a suitable mechanism of curing was suggested. The corrosion protective performance of conventional polyamide cured epoxy and PANI cured epoxy coating on steel has been assessed in 3% NaCl by electrochemical impedance spectroscopy (EIS). The self-healing property of the PANI cured epoxy coating on steel in 3% NaCl was studied by scanning vibrating electrode technique (SVET).