Corrosion protective bi‐layered composites of polyaniline and poly(o‐anisidine) on low carbon steel

Bi‐layered composites of polyaniline (PANI) and poly(o‐anisidine) (POA) were investigated for corrosion protection of low carbon steel (LCS). In this work, homopolymers and bi‐layers of PANI and POA were electropolymerized on LCS from an aqueous salicylate solution by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Corrosion tests were carried out in aqueous 3% NaCl solution for LCS coated with PANI, POA, bi‐layered POA/PANI (POA on top of the PANI) or PANI/POA (PANI on top of the POA) composites using open circuit potential (OCP) measurements, potentiodynamic polarization technique, and electrochemical impedance spectroscopy (EIS). The single layer of PANI and POA protected the LCS in 3% NaCl for 8 and 16 h, respectively. The bi‐layered composite coatings provide effective protection to LCS for a longer time than a single layered PANI or POA coating. However, the corrosion protection offered to LCS depends on the deposition order of polymer layers in the composite. The PANI/POA composite provides better protection to LCS against corrosion than POA/PANI coating. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and corrosion protection aspects of poly(<Emphasis Type="Italic">o</Emphasis>-toluidine)/CdO nanoparticle composite coatings on mild steel

This study examines the possibility of using poly(o-toluidine)/CdO (POT-CdO) nanoparticle composite coating for corrosion protection of mild steel in chloride environment. The POT-CdO nanoparticle composite coating was synthesized on mild steel from aqueous tartrate solution containing CdO-nanoparticles (size ~18 nm) by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, UV–Visible absorption spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction measurements. The corrosion protection aspects of the resulting POT-CdO nanocomposite structure were investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy. The results of these investigations reveal that the POT-CdO nanoparticle composite acts as a protective coating on mild steel and reduces the corrosion rate of mild steel almost by factor of 70.     

Comparison of the corrosion protection of mild steel by polypyrrole–phosphate and polypyrrole–tungstenate coatings

The electrodeposition of polypyrrole–phosphate (PPy–P) and polypyrrole–tungstenate (PPy–W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy–P and PPy–W films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) and tungstenate (PPy–W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open‐circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–W coatings could provide much better protection than the PPy–P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X‐ray analyses. The results reveal that the PPy–P and PPy–W coated electrodes offered a noticeable enhancement in protection against corrosion processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

聚吡咯的绿色制备及其环氧树脂复合涂层对Q235钢的防腐性能

采用一种绿色、温和的氧化体系（H2O/FeCl2/H2O2）合成了结构规整的聚吡咯纳米微球,其结构和形貌采用FTIR和SEM进行表征。以聚吡咯为功能成分,环氧树脂为成膜物质,制备了聚吡咯/环氧树脂复合涂层,研究了其复合涂层在3.0% NaCl溶液中的防腐性能（EIS曲线、开路电位、Tafel极化曲线）,结果表明0.6% Ppy-H复合涂层在3.0% NaCl溶液中浸没60天后,仍表现出高的涂层电阻（5.14×107 Ω?cm2）和腐蚀电位 （Vcorr = ?0.202 mV）。     

Study on electrochemical behavior of Nano‐ZnO modified alkyd‐based waterborne coatings

A nano‐composite coating was formed using nano‐ZnO as pigment in different concentrations, to a specially developed alkyd‐based waterborne coating. The nano‐ZnO modified composite coatings were applied on mild steel substrate by dipping. The dispersion of nano‐ZnO particles in coating system was investigated by scanning electron microscopic and atomic force microscopic techniques. The effect of the addition of these nano‐pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy. Coating modified with higher concentration of nano‐ZnO particles showed comparatively better performance as was evident from the pore resistance (R_po) and coating capacitance (C_c) values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano‐particle modified coatings as compared with the neat coating, confirming the positive effect of nano‐particle addition in coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of poly(aniline‐co‐o‐toluidine) coatings and their corrosion‐protection performance on low‐carbon steel

Strongly adherent poly(aniline‐co‐o‐toluidine) coatings were synthesized on low‐carbon‐steel substrates by the electrochemical copolymerization of aniline with o‐toluidine with sodium tartrate as the supporting electrolyte. These coatings were characterized with cyclic voltammetry, ultraviolet–visible absorption spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and scanning electron microscopy. The formation of the copolymer with the mixture of monomers in the aqueous sodium tartrate solution was ascertained by a critical comparison of the results obtained from the polymerizations of the individual monomers, aniline and o‐toluidine. The optical absorption spectrum of the copolymer was drastically different from the spectra of the respective homopolymers, polyaniline and poly(o‐toluidine). The extent of the corrosion protection offered by poly(aniline‐co‐o‐toluidine) coatings to low‐carbon steel was investigated in aqueous 3% NaCl solutions by open‐circuit‐potential measurements and a potentiodynamic polarization technique. The results of the potentiodynamic polarization measurements showed that the poly(aniline‐co‐o‐toluidine) coatings provided more effective corrosion protection to low‐carbon steel than the respective homopolymers. The corrosion rate depended on the feed ratio of o‐toluidine used for the synthesis of the copolymer coatings. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:1868–1878, 2007     

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.     

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.     

Laboratory evaluation of corrosion resistance at metallic substrates by an organic coating: delamination effects

The corrosion behaviour of an epoxy-polyamide primer applied on galvanized steel specimens during immersion in 3% NaCl aqueous solution was examined by electrochemical impedance spectroscopy (EIS). The investigation of both intact and defective coatings allowed for the comparison of their electrochemical behaviours in order to assess the anticorrosive characteristics of the system. The impedance response of the intact coating was found to correspond to a porous film presenting localised electrochemically active areas, in which the precipitation of zinc-containing corrosion products contributes to the sealing of the coating. Conversely, scribed defects cannot be spontaneously sealed and no effective protection of the metal can be achieved.     

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.     

Corrosion protection of mild steel by polypyrrole phosphate composite coating

Electrodeposition of polypyrrole phosphate (PPy–P) on mild steel (ST₁₂) was achieved in oxalic acid medium using cyclic voltammetry (CV) technique. Adherent and homogeneous PPy–P films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) coatings in 3.5% NaCl solutions was investigated through potentiodynamic polarization technique, open circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). Based on a physical model for the corrosion of mild steel composite, the Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–P coatings could provide much better protection than PPy. The effect of phosphate on the morphology and structure of the passive film was investigated by scanning electron microscopy and electron dispersion X-ray analysis (EDX). The results reveal that the PPy–P coated electrode provided a noticeable enhancement of protection against corrosion process.     

Corrosion performance of chemically synthesized poly(aniline-co-o-toluidine) copolymer coating on mild steel

A soluble copolymer from aniline and o-toluidine [poly(aniline-co-o-toluidine)] was synthesized by chemical oxidative copolymerization using ammonium persulphate as an oxidant in hydrochloride aqueous medium. The resultant copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy and chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of copolymer coating was investigated in major corrosive environments, such as 0.1 M HCl, 5% NaCl solution, artificial seawater, distilled water and open atmosphere by conducting various corrosion tests which include: immersion test, open circuit potential (OCP) measurements, potentiodynamic polarization measurements and atmospheric exposure test. The corrosion performance of copolymer coating was also compared separately with polyaniline (PANi) and poly(o-toluidine) (POT) homopolymer coatings. The surface morphologies of polymer coatings were evaluated using scanning electron microscopy (SEM). The synthesized copolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 78–94% after 30 days of immersion. The corrosion performance of copolymer in 5% NaCl and artificial seawater was comparable, which was only marginally better than in 0.1 M HCl. In general, the performance of copolymer coating was found to be better than that of homopolymer coatings.     

Styrene butadiene co-polymer based conducting polymer composite as an effective corrosion protective coating

Electroactive conducting polymer composite coatings of polyaniline (PANI) are electrosynthesized on styrene–butadiene rubber (SBR) coated stainless steel electrode by potentiostatic method using aqueous H₂SO₄ as supporting electrolyte. The protective behaviour of these coatings in different corrosion media (3.5% NaCl and 0.5 M HCl) is investigated using Tafel polarization curves, open circuit potential measurements and electrochemical impedance spectroscopy. The results reveal that SBR/PANI composite coating is much better in corrosion protection than simple PANI coating. The corrosion potential of composite films shifts to more noble values indicating that SBR/PANI composite coating act as an effective corrosion protective layer.     

Enhancing corrosion resistance of aluminum composites in 3.5% NaCl using pigmented epoxy fluoropolymer

The corrosion protection performance of AA6061 T6–10% Al₂O₃ composite, coated with four different fluoropolymer paint systems, were investigated in 3.5% NaCl aqueous solutions under uniform and scratched conditions. A comparison between epoxy-treated clear and pigmented fluoropolymer coatings with newly developed vanadate-based fluoropolymer coatings was performed from corrosion protection, adhesion and durability points of view. The corrosion rates of epoxy-treated clear FLBZ 1074 increased dramatically after less than one month of exposure in 3.5% NaCl aqueous solutions. The addition of iron oxide or titanium oxide as pigments to the fluoropolymer decreased the porosity of epoxy and hence, improved the corrosion resistance. The newly developed vanadate based-clear FLBZ 1074 system showed outstanding corrosion resistance even after two months of immersion in 3.5% NaCl aqueous solutions under scratched coating conditions. The durability of such new coating based on salt spray test results was very promising (>2000 h without any sign of corrosion). The vanadate-pigmented FLBZ 1074 showed a dramatic increase in the corrosion rates. Moreover, the presence of pigments affected negatively the adhesion performance as well as the durability of the coating. A general model has been used to analyze the impedance data in terms of reactions occurring during the interaction of the coated metal with the environment. It was found that the vanadate-treated specimens not only improve the protective power against filiform corrosion as a factor of time, but also maintain the adhesion performance within the acceptable ranges.     

The long-term effectiveness and failure mechanism of the chemically bonded phosphate ceramic coatings with different thickness

In this study, the chemically bonded phosphate ceramic coatings (CBPCs) with different thickness (100 µm, 200 µm, and 300 µm) are prepared on the mild steel (Q235). Potentiodynamic polarization testing and electrochemical impedance spectroscopy were carried out to study the synthetic effect of coating thickness and etching time (12, 24, 36, and 48 hours) on the corrosion behavior of CBPCs. The surface and cross section microstructure of CBPCs before and after different immersion time in 3.5 wt.% NaCl solution is investigated to better understand the corrosion behavior. Results revealed that the enhanced coating thickness can effectively postpone the corrosive factors infiltration into the substrate and prohibit the corrosion of the mild steel. From the potentiodynamic polarization testing results, the protection efficiency of the coating greatly increases with the increase in etching time. In addition, an increase in 10 000 and 1000 orders of magnitude of impedance value for the CBPCs with 12 hours and 48 hours etching time has been observed, respectively, indicating the CBPCs can effectively protect the mild steel from corrosion damage even with long-term service.     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.     

Electropolymerization of aniline in phosphonium‐based ionic liquids and their application as protective films against corrosion

Conductive polyaniline (PANI) films were deposited on mild steel by an electropolymerization technique in the presence of different types of phosphonium‐based ionic liquids, including tetrabutylphosphonium bromide, tetraoctylphosphonium bromide, and ethyltributylphosphonium diethylphosphate. The formation of the PANI films was followed by repetitive cyclic voltammetry scans and was confirmed with diffuse reflectance infrared Fourier transform spectroscopy. The morphology, surface roughness parameters, and grain sizes of these coatings were evaluated by atomic force microscopy. The corrosion behavior of the bare and PANI‐coated electrodes was investigated by potentiodynamic polarization, open‐circuit potential, and electrochemical impedance spectroscopy techniques in a simulated marine environment in 3.5 wt % aqueous NaCl solutions. The quantum chemical parameters of the PANI composite films were also calculated with parametric method 3, a semi‐empirical quantum mechanical method. The theoretical conclusions were found to be consistent with the reported experimental data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43923.     

Service life prediction of organic coatings: electrochemical impedance spectroscopy vs actual service life

Electrochemical impedance spectroscopy (EIS) is used to derive an expression for predicting the service life of organic coating in a C4-type environment (industrial and costal areas with moderate salinity) as defined in ISO 12944 standard for paints and varnishes—corrosion protection of steel structures by protective paint systems. Three coating systems with a record of 2, 5, and 10 years of durability were selected for the study. The selection was also based on proven composition and dry film thickness (DFT) of the coatings as per ISO 12944. Electrochemical impedance measurements of the paint-coated panels were carried out by exposing the coated mild steel panels without scribe in different corrosive environments such as immersion in NaCl solution, neutral salt spray, etc. Neutral salt spray exposure was found to be the most severe corrosive environment among all the three coating systems. In most of the cases, EIS gave early indication of coating failure when compared to visual defects such as blistering and over-film corrosion.     

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.     

Poly(N-ethylaniline) coatings on 304 stainless steel for corrosion protection in aqueous HCl and NaCl solutions

Poly(N-ethylaniline) (PNEA) coatings were grown by potentiodynamic synthesis technique on 304 stainless steel (SS) alloy from 0.1 M of N-ethylaniline (NEA) in 0.3 M oxalic acid solution. Characterization of adhesive and electroactive PNEA coatings was carried out by cyclic voltammetry, FT-IR spectroscopy and scanning electron microscopy (SEM) techniques. The protective properties of PNEA coatings on SS were elucidated using linear anodic potentiodynamic polarization, Tafel and electrochemical impedance spectroscopy (EIS) test techniques, in highly aggressive 0.5 M HCl and 0.5 M NaCl solutions. Linear anodic potentiodynamic polarization test results proved that PNEA coating improved the degree of protection against pitting corrosion in HCl and NaCl solutions. Tafel test results showed that PNEA coating appears to enhancement protection for SS in 0.5 M NaCl and 0.5 M HCl solutions. However, according to long-term EIS results, PNEA coating is better for the protection of SS electrodes during the long immersion period in NaCl compared to that in HCl medium.