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.     

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 resistant behaviour of PANI–metal bilayer coatings

The present work discusses on the corrosion resistant behaviour of polymer metal bilayer coatings, viz. polyaniline (PANI), polyaniline–nickel (PANI–Ni), nickel–polyaniline (Ni–PANI), polyaniline–zinc (PANI–Zn) and zinc–polyaniline (Zn–PANI). The coatings were synthesized by means of cyclic voltametric method. The coatings thus obtained were uniform in nature and highly adherent to the mild steel substrate. The effectiveness of the coatings in preventing corrosion was tested by electrochemical impedance studies (EIS) using Nyquist and Bode plots and potentiodynamic polarization studies as well. Among the various coatings synthesized, the PANI–Zn coating was found to offer the maximum protection, followed by PANI–Ni coatings. Metal–PANI coatings were found to offer the least resistance to corrosion. The coatings thus obtained were characterized by scanning electron microscopic (SEM) analysis and the results are discussed.     

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.     

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     

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     

Electrosynthesis and protection role of polyaniline–polvinylalcohol composite on stainless steel

Polyaniline–polyvinyl alcohol (PANI–PVA) composite has been electrodeposited on stainless steel surface from aqueous sulfuric acid solution of aniline monomer in presence of soluble PVA at different concentrations. The PVA increased the rate of electropolymerization where 4 g/L PVA formed a composite of 37 wt% PANI and 63 wt% PVA composition. The composite layer exhibited more adhesion to the steel surface in comparison with PANI layer but with less thermal stability. It has higher protection role for the stainless steel (SS) against general and pitting corrosion. It enhanced the passivation of the SS surface by increasing the thickness of oxide film and improving the composition.     

Electrochemical synthesis and corrosion performance of poly(pyrrole-co-o-anisidine)

The electrochemical synthesis of poly(o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole:o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly(o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly(o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.     

Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution

The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1 M sulfuric acid solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm⁻². Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1 M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.     

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.     

Synthesis of nano polyaniline and poly-<Emphasis Type="Italic">o</Emphasis>-anisidine and applications in alkyd paint formulation to enhance the corrosion resistivity of mild steel

Protection of oxidizable metals against corrosion has now being intensively investigated, by applying or developing different methods such as coatings and conversion films; however, all reported methods involve environmentally hazardous materials. Conducting polymers have now been used as corrosion inhibitor coatings that are either chemically or electrochemically deposited on the metal substrate. The application of nanotechnology in the corrosion protection of metals has recently gained momentum. Environmental impact can also be improved by utilizing nanostructure particulates in coatings and eliminating the requirement of toxic solvents. We report here the synthesis of nanoparticles of polyaniline (PANI) and poly-o-anisidine (POA) using emulsion polymerization method in micellar solution of SDS and their anticorrosive property has been experimentally checked. The prepared nanoparticles have been characterized by FTIR and TEM. The nanoparticles of the synthesized polymers were dispersed in alkyd paint formulation for coatings on the metal surface (mild steel). The water absorption in the prepared coatings was also studied. The corrosion rate of polymeric film was determined by weight loss measurement and the surface morphology was examined by SEM. The nano PANI/Alkyd coatings showed considerable protection against corrosion than the POA/alkyd coatings.     

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.     

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.     

Conducting polymer based hybrid nano-composites for enhanced corrosion protective coatings

Hybrid composite coatings containing zinc oxide (ZnO) and polyaniline (PANI) as nano-additives dispersions were prepared with poly(vinyl acetate) (PVAc) as the major matrix. The steel plates dip-coated with these formulations were tested for corrosion protection by immersion in saline water over long periods. The Tafel plots for the determination of open circuit potential (OCP) and corrosion current (I_corr) were recorded. The coatings containing both ZnO and PANI showed improved corrosion resistance as compared to the single component coating. The I_corr values of PVAc–ZnO–PANI are found to be two-order magnitude lower than that of PVAc and PVAc–ZnO coatings. The results are explained on the basis of enhancement in barrier properties due to nano-particulate additives in PVAc–ZnO–PANI film together with the redox behaviour of PANI and protective oxide layer formation near the substrate.     

High performance corrosion protective DGEBA/polypyrrole composite coatings

Conducting polymers (CP) have been envisaged as nontoxic substitutes for chromates in corrosion protective coatings owing to their environmental stability, excellent corrosion resistant performances and good adhesion to metal substrate. Recent advancements in the field of corrosion protective coatings have therefore headed towards the utilization of conducting polymers as “smart corrosion inhibitors” in the formulation of eco-friendly anti-corrosive coatings. With the aim to develop a facile method for the synthesis of anti corrosive coating material having superior corrosion protective properties, the present work reports the corrosion studies of polypyrrole/DGEBA composite coatings on mild steel (MS). The coatings were characterized by physicochemical as well as physicomechanical studies while the corrosion protective performance was evaluated by chemical resistance in different corrosive media, corrosion rate and open circuit potential (OCP) measurements. The morphologies of corroded, coated, uncorroded and uncoated samples were investigated by SEM studies. The composite coatings were found to show far superior anti corrosive performance than PANI/epoxy coatings in acid, alkaline as well as saline environments.     

Conducting polymer based hybrid nano-composites for enhanced corrosion protective coatings

Hybrid composite coatings containing zinc oxide (ZnO) and polyaniline (PANI) as nano-additives dispersions were prepared with poly(vinyl acetate) (PVAc) as the major matrix. The steel plates dip-coated with these formulations were tested for corrosion protection by immersion in saline water over long periods. The Tafel plots for the determination of open circuit potential (OCP) and corrosion current (I_corr) were recorded. The coatings containing both ZnO and PANI showed improved corrosion resistance as compared to the single component coating. The I_corr values of PVAc–ZnO–PANI are found to be two-order magnitude lower than that of PVAc and PVAc–ZnO coatings. The results are explained on the basis of enhancement in barrier properties due to nano-particulate additives in PVAc–ZnO–PANI film together with the redox behaviour of PANI and protective oxide layer formation near the substrate.     

Designing of corrosion resistant epoxy coatings embedded with polypyrrole/SiO2 composite

Polypyrrole/SiO₂ composite was synthesized by chemical oxidative polymerization of pyrrole using FeCl₃. The synthesized polymer composite was loaded in epoxy resin to develop coatings for mild steel substrates using powder coating technique. SEM and TEM images reveal homogenous dispersion of SiO₂ particles in polypyrrole matrix. TGA analysis confirms good thermal stability of the polymer composite. Tafel polarization and electrochemical impedance spectroscopy (EIS) results exhibit remarkably high corrosion protection efficiency of epoxy coatings with polymer composite in 3.5% NaCl solution. Corrosion studies of coatings with an artificial defect reveal the passivation of defect by the polymer composite present in the epoxy coatings. Salt spray test results revealed superior corrosion resistance offered by the polymer composite.     

聚苯胺修饰纳米ZnO薄膜及其光致阴极保护性能

从金属材料腐蚀特性及腐蚀保护要求出发,首先利用阳极氧化法制得ZnO薄膜,再通过恒电位法将ZnO薄膜用聚苯胺修饰得到ZnO/PANI复合薄膜。采用扫描电镜分析（SEM）、X射线衍射分析（XRD）、光电流、开路电位（OCP）及电化学阻抗等方法对制得的ZnO薄膜和ZnO/PANI复合薄膜进行物性分析和光电性能评价。研究表明：成功制得ZnO/PANI复合薄膜,且表现出优良的腐蚀保护性能。OCP实验表明,ZnO/PANI复合薄膜腐蚀保护性能与纳米ZnO薄膜相比提升了2～3倍。其中,光照后ZnO薄膜的光电流增加7μA,OCP下降5mV,复合薄膜的光电流增加22μA,OCP下降13mV。最后,失重实验对两种薄膜的光致阴极保护性能的分析数据显示,ZnO薄膜和ZnO/PANI复合薄膜都能对316L不锈钢和Q235碳钢起到光致阴极保护效果,但复合薄膜对316L不锈钢的保护效果尤为明显,其受腐蚀速率与在ZnO薄膜保护状态下相比降低了1倍以上。     

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.     

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.