Corrosion Protection of Stainless Steel by Polyaniline/Polypyrrole Composite Coating

Department of Technology, Annamalai University, nagar -608 002, Annamalai
International Journal of Engineering Science and Technology 01/2010; 2:7105-7111.

ABSTRACT Electrochemical deposition of polyaniline/polypyrrole coatings on stainless steel was carried out by the constant potential technique. The surface properties and corrosion behavior of the coatings were studied by varying the time of deposition and the initial monomer concentration. The corrosion current and corrosion potential were measured by direct current polarization test. The changes in corrosion current and corrosion potential with the deposition time and the initial monomer concentration were thoroughly investigated. The surface energy of coated stainless steel was calculated by using dynamic contact angle analyzer.

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    ABSTRACT: Polyaniline (PANI) salts doped with inorganic acids (HCl, H2SO4 and H3PO4) were directly synthesized by using solid-state polymerization method. The FTIR spectra, UV–vis absorption spectra and X-ray diffraction patterns were used to characterize the molecular structures of the PANI salts. Voltammetric study was done to investigate the electrochemical behaviors of all these PANI salts. The PANI salts were affected by varying the protonation media (HCl, H2SO4 and H3PO4). The FTIR and UV–vis absorption spectra revealed that all PANI salts contained the conducting emeraldine salt phase at different oxidation state. The crystallinity of PANI doped with HCl was better than those doped with H2SO4 and H3PO4. The conductivity of the PANI doped with HCl is the highest among the inorganic acid doped PANI.
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    ABSTRACT: The anti-corrosion performance of polyaniline coated mild steel samples exposed to artificial brine and dilute hydrochloric acid environments was evaluated. Samples of mild steel (UNS G10100) coated with polyaniline deposited from solution, and overcoated with an epoxy barrier paint, when scratched to expose precise areas of bare metal, exhibited corrosion rates in aqueous 3.5% NaCl solutions 2 times less, and in 0.1 N HCl solutions, 100 times less than observed on identical samples coated with epoxy paint alone. Mechanistic information, and quantitative corrosion rates were obtained by Tafel Extrapolation, Potentiodynamic Polarization, Galvanic Coupling and Electrochemical Impedance Spectroscopic techniques. These studies, in conjunction with surface analysis by ESCA and Auger techniques, indicate that the corrosion protection, even for exposed bare steel areas, occurs by the formation of passivating iron oxide (γ - Fe2O3 and Fe3O4) surface layers. The formation of these specific oxide layers occurs when the polyaniline is galvanically coupled to the steel. This is evident by the fact that the dimensions of the exposed bare steel area that can be protected in a scratch can be large, but are limited in each corrosion environment.
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    ABSTRACT: Preparation and characterization of highly conducting polyaniline (PANI) doped with picric acid (PA) was proved with the help of various techniques. Elemental analysis, FTIR and XPS spectroscopic measurements confirm that the PA operates as a protonating agent to induce the internal conversion of PANI emeraldine base (PANI-EB) to the PANI emeraldine salt (PANI-ES) with the doping level 50%. Molecular modeling calculations (MM+) showed that the optimum geometric structure of 2PA:1PANI (energy 38.231388 kcal/mol, and gradient 0.065246).The observed higher conductivity (σ ∼150 S/cm) of PA-doped PANI film prepared at molar ratio 2PA:1PANI (EB) is attributed to the change in the molecular conformation from coil to expanded coil-like. PA-doped PANI is thermally unstable above ∼135 °C and the thermal processing with other insulating matrix is not profitable but the solution casting is highly promising. PA-doped PANI with acrylonitrile-butadiene-styrene copolymer has been fabricated and showed the threshold value ∼4 wt.% of a conducting material. The reduced PA-doped PANI reveals an ability to store electrical energy of about 110.43 Wh/kg in a condensed lightweight form. The immediate decoloration of the dark green () PANI after addition of 5.5 μg/ml KMnO4 in strong acid medium (pH 1.0, H2SO4, 40% DMF) is due to the highest oxidized form of PANI. Increasing the absorbance with increases in the KMnO4 concentration (μg/ml) at ∼385 nm has been successfully applied to the determination of trace amount (0.55 μg/ml) of Mn(VII) in a synthetic solution.
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