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.     

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 coating containing polyaniline glass flake composite for steel

Corrosion protection of steel by glass flake (GF) containing coatings is widely used in marine atmosphere. Even though, the coatings containing glass flake are highly corrosion resistant, their performance is decreased due to the presence of pinholes and coating defects. It is well established that polyaniline containing coating is able to protect the pinhole defects in the coatings due to passivating ability of polyaniline. Hence a study has been made on the corrosion protection ability of steel using polyaniline-glass flake composite containing coating with 10% loading of glass flake in epoxy binder. The polyaniline glass flake composite (PGFC) was synthesized by chemical oxidation of aniline by ammonium persulphate in presence of glass flake. The corrosion protection ability of GF and PGFC containing coating on steel was found out by salt spray test and EIS test in 3% NaCl. In both the tests, the resistance value of the PGFC containing coating has remained at 10⁸-10⁹ Ω cm² where as for the GF containing coating, the resistance values decreased to 10⁵ Ω cm². The enhanced corrosion protection ability of the PGFC containing coating is due to the passivation ability of the polyaniline present in the coating.     

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.     

Soluble polyanilines obtained by nucleophilic addition of arenesulphinic acids

Polyaniline powder and films can be modified by nucleophilic addition of arenesulphinic acids to oxidized forms of polyaniline. The FTIR spectra of modified polymers suggest the formation of sulphone and/or sulphonamide moieties linked to the polymer backbone. The modification degree increases with the increasing of the oxidation state of the polymer. The addition decreases significantly at pH above 7. It is proposed a mechanism of nucleophilic addition, which explains the effect of the oxidation state of the polymer and pH of the solution. The modification increases the solubility of the polymers in common organic solvents. The modification reaction seems to provide a simple pathway to the incorporation of organic moieties to polyaniline backbone.     

Corrosion protection of carbon steel and copper by polyaniline and poly(ortho-methoxyaniline) films in sodium chloride medium. Electrochemical and morphological study

The aim of this work was to obtain polyaniline (Pani) and poly(ortho-methoxyaniline) (Poma) by chemical synthesis and to evaluate their corrosion protection properties on carbon steel (CS) and copper (Cu) in an aggressive media such as sodium chloride. The syntheses of the polymers were carried out by chemical oxidation of the monomers by (NH₄)₂S₂O₈ in nitric acid solutions. Under these conditions, the polymers were obtained in the oxidized form, dissolved in 1-methyl-2-pyrrolidone and casted by solvent evaporation onto the metallic substrates (carbon steel and copper) for corrosion evaluation. The morphology of the polymers was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical behavior was determined by open circuit potential (OCP) measurements and polarization curves (PC). The best results were obtained with Pani because this polymer film participates in the formation of an oxide film at the polymer–metal interface, a phenomenon which is not observed with Poma. This oxide film increases the barrier effect that the polymeric film has by itself.     

Engineering detonation nanodiamond - Polyaniline composites by electrochemical routes: Structural features and functional characterizations

Novel detonation nanodiamond (DND) - polyaniline (PANI) composite systems have been prepared by electrochemical polymerization techniques. Thanks to the use of two different electrochemical methods, i.e. cyclic voltammetry and chronoamperometry, it has been possible to emphasize the influence of DND particles on the nucleation mechanism of the conducting polymer. In particular, the presence of DND into the reaction environment has proven to modulate the organization of the aniline oligomers into π-stacked aggregates and to induce the production of one-dimensional nanostructures. Scanning and transmission electron microscopy was used to investigate the morphology of the final composites. The protonated conducting form of the PANI matrix has been evidenced by Raman spectroscopy and the ionic/electronic transport of the PANI-DND systems was tested by means of electrocatalysis measurements toward the iodine/iodide redox couple. Based on the present experimental data, the use of nanodiamond as filler for conducting polymer based nanocomposite represents not only a fascinating challenge for the production of advanced technological applications but it can also be exploited for the controlled growth of polymeric units and for the fabrication of tailored polymeric architectures.     

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.     

Study of polyaniline films degradation by thin-layer bidimensional spectroelectrochemistry

Degradation of polyaniline films electrodeposited on optically transparent gold electrodes has been followed by thin-layer bidimensional spectroelectrochemistry. The influence of the anodic potential reached during multiple potential scans has been assessed. Correlation of changes in the spectral signals in normal and parallel arrangement has enabled identifying species of different nature, both soluble and insoluble, electroactive and inert, during the degradation of the polymer film. The three bidimensional spectroelectrochemistry signals have demonstrated the occurrence of different types of degradation processes depending on the applied potential, ranging from the simple release of oligomers and hydrolysis products retained in the film during electropolymerization to more dramatic modifications of the film.     

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).     

Silver electrocrystallization at polyaniline-coated electrodes

The initial stage of silver electrocrystallization is studied at polyaniline (PANI)-coated platinum electrodes by means of potentiostatic current transients and electron microscopic observations. Data for the nucleation frequency and the number of active sites for nucleation are obtained by interpreting of current transients according to the theory for nucleation and 3D growth under diffusion limitations. It is found that depending on the PANI layers thickness, d, two different regimes for silver nucleation and growth exist. For thin PANI coatings (d<0.3 μm), the crystallization occurs with high nucleation frequency at active sites located at the polymer layer/metal electrode interface, the number of active sites decreasing sharply with increasing PANI coverage. For thick PANI layers (d>0.3 μm), silver nucleation occurs with a two orders of magnitude lower nucleation frequency at active sites located most probably at the polymer surface, their number remaining constant for thicknesses up to 1.4 μm. It is established that reduction of the PANI layer occurring in parallel with the silver electrodeposition does not influence the number of active sites for nucleation. The results obtained by interpretation of current transients are in good agreement with results for the number of crystals obtained by microscopic observation.     

聚邻甲苯胺防腐涂层对碳钢的腐蚀保护作用

离分子聚苯胺及其衍生物具有良好的电活性。本文介绍了聚邻甲苯胺的合成,并利用线性极化法和动电位扫描极化曲线拟合法研究了聚邻甲苯胺涂覆碳钢电极在０．１ｍｏｌ／Ｌ盐酸溶液中的腐蚀行为。试验发现：用聚邻甲苯胺作底漆、环氧作面漆的复合涂层大大提高了碳钢电极的检化电阻,减小了其腐蚀电流。其对碳钢的腐蚀保护作用主要是由于掺杂态聚邻甲苯胺的电活性。     

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.     

Electrochemical synthesis of polyaniline in the presence of poly(amidosulfonic acid)s with different rigidity of polymer backbone and characterization of the films obtained

We have studied electrochemical matrix polymerization of aniline in the presence of poly(amidosulfonic acid)s of different nature: poly(2-acrylamido-2-methyl-1-propanosulfonic acid) (PAMPSA, flexible backbone); poly(p,p′-(2,2′-disulfoacid)-diphenylene-iso-phthalamid) (i-PASA, semi-rigid backbone); poly(p,p′-(2,2′-disulfoacid)-diphelylene-tere-phthalamid) (t-PASA, rigid backbone). Also, we have investigated spectral and electrochemical properties of the films obtained, as well as their surface morphology. The matrix polymerization results in the formation of interpolymer complexes of polyaniline (PANI) and the above-cited polyacids. The acceleration of aniline electropolymerization in the presence of poly(amidosulfonic acid)s was observed due to association of aniline molecules to sulfonic groups of the polyacid and higher local concentration of protons near the polyacid backbone. The rigid-chain polyacids interfere with the normal course of the electropolymerization, which manifests itself in the changes of the shape of time dependences of absorbance and charge. Cyclic voltammetry and spectroelectrochemical experiments showed that the formation of interpolymer complex with rigid-chain polyacids distorts spectroelectrochemical characteristics of PANI. This evidently results from steric hindrances in the formation of quinoid units.     

纳米TiO2涂层在低碳钢上的防腐蚀性能

采用溶胶-凝胶法与浸渍提拉法在经过黑化处理后的普通低碳钢上制备了纳米TiO2涂层。分别研究了不同热处理温度以及不同提拉次数所得的纳米TiO2/Ironoxides/Fe在25g/LNaHCO3溶液中,在无光照和紫外光照射下的腐蚀电位。结果表明,在无光照和紫外光照射下,纳米TiO2/Ironox-ides/Fe的腐蚀电位均低于基体的腐蚀电位。纳米TiO2涂层可作为光生阳极从而对低碳钢基体起到阴极保护作用。其最佳工艺条件为提拉4~5次,400℃下热处理1h。     

Influence of electrode geometry on the redox switching characteristics of conducting polymers

The dimensions of working electrodes relative to those of conducting polymer films have been found to influence the redox switching characteristics of polymer films. Using microband electrode arrays, the electrodes were operated either altogether as a single electrode or individually as the working electrode, leading to a large difference in the contact area between the electrode and the overlaying polymer film. When the microband electrodes were operated altogether, the voltammetric peak potential was significantly lower and the rate of oxidation was much faster than when the electrodes were operated individually. Each electrode within the array can also be operated individually (i.e. with equivalent contact area) to address the polymer from different positions across the film. An individual electrode located towards the edge of the film gave rise to higher oxidation peak potentials and slower rates of oxidation when compared to an electrode situated towards the centre of the film. Potentiometric measurements of electrodes situated adjacent to the working electrode showed that the rate of the oxidation was controlled by the propagation of the interface between the conducting and insulating phases [1].     

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.     

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.     

Fabrication of Schottky diode based on Zn electrode and polyaniline doped with 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt

The electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, of ITO/polyaniline/Al and ITO/polyaniline/Zn Schottky diodes have been investigated. Polyaniline (PANI) was prepared chemically and doped with 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPSNa). The maximum conductivity value for PANI-AMPSNa films was 1.8 × 10⁻² S/cm at 0.5 weight ratio of AMPSNa. The values of various junction parameters such as ideality factor, barrier height and charge carrier concentration were calculated based on the thermionic emission theory. Zn electrode showed better rectifying behavior with PANI-AMPSNa film than Al electrode. The obtained C-V characteristics showed that the charge carrier concentration is in the range of 10¹⁶/cm³.     

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.