Effect of current density on the corrosion protection performance of polyaniline coated AISI 4140 steel

The present work reports on electropolymerisation of aniline onto AISI 4140 steel substrate at room temperature in oxalic acid media by the potentiodynamic electrodeposition method. The effect of coating current density on the morphology of conductive polymer films and their corrosion behaviour has been investigated. The electrolyte solution comprised 0.1 M aniline?+?0.3 M oxalic acid. The effects of deposition current density changes (0.1, 0.2, 0.3, 0.4 and 0.5?mA cm^?2) on the films were investigated. The PANI film was characterised using cyclic voltammetry and optical microscopy; it was covered with a dark green-yellow homopolymer film of strongly adherent homogeneous characteristic. The corrosion behaviour of steel electrodes with and without polyaniline (PANI) film in 3.5 wt-% NaCl solution was investigated through anodic polarisation curves. The results indicated that the PANI coating obtained under 0.2?mA cm^?2 was the most corrosion protective.     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.     

One-Step Synthesis of the Polyaniline–Single-Walled Carbon Tubes Nanocomposite in Formic Acid and Its Electrochemical Properties

A one-step synthesis of a stable dispersion of nanocomposite consisting of polyaniline (PANI) and single-walled carbon nanotubes (SWCNTs) was carried out by the oxidative polymerization of aniline with benzoyl peroxide (PB) in concentrated formic acid (FA). Electrically conductive film coatings were obtained by direct application of this dispersion to an electrode. The coatings have high specific electrochemical capacitance and stability during prolonged cycling in an aprotic electrolyte (1 M LiBF₄ in γ-butyrolactone).     

Exploration of the formation mechanisms of polyaniline nanotubes and nanofibers through a template-free method

This study reports the polymerization of aniline monomers in different HCl concentrations to investigate the formation mechanisms of one-dimensional polyaniline (PANI) nanostructures. Fourier transform infrared (FT-IR) spectra indicate that the products obtained in different acidic solutions have different molecular structures. In low-acidity conditions (HCl concentration ≤0.1 M), aniline monomers form phenazine-like aniline units in the initial reaction stage. As the reaction continues, a structure consisting of a head of phenazine-like aniline units and a tail of para-linked aniline units develops. By contrast, the reaction only produces para-linked aniline units as the concentration of HCl increases to 0.2 M. PANI products with different molecular structures exhibit different shapes, including nanotubes and nanofibers. For nanotubes, electron microscopy images reveal the flake-like intermediates formed in the initial reaction stage and then curl into nanotubes as the reaction proceeds. The phenazine-like aniline units serve as the axis for PANI nanotube curling. On the other hand, the para-linked aniline units act as a template for the formation of PANI nanofibers. This study demonstrates the formation mechanisms of PANI nanotubes and nanofibers. The acid concentration in the polymerization solution is the critical factor determining whether the aniline monomers form nanotubes or nanofibers.     

Dependence of the corrosion performance of polyaniline films applied on stainless steel on the nature of electropolymerisation solution

Polyaniline (PANI) films were deposited under cyclic voltammetric conditions on 304L stainless steel by aniline electropolymerisation from acidic and slightly basic solutions containing respectively the followed support-electrolytes: H₂C₂O₄ and KNO₃.It was found that the film produced in oxalic acidic medium was more conductive than that obtained in potassium nitrate one.The PANI coatings corrosion performances in 0.5 M NaCl were investigated and compared using standard electrochemical methods, electrochemical impedance spectroscopy (EIS) and SEM analysis.The highest corrosion resisting efficiency was obtained for PANI_nitrate which exhibited a significant physical barrier property against the attack of corrosive products. However, the corrosion protection of conductive PANI_oxalic coating was related to its catalytic behavior.     

Comparison study on anticorrosion performances of the epoxy coatings with two different nano‐polyanilines for Q235 steel

Sulfuric acid doped nano‐polyaniline was prepared by direct mixed oxidation in two different systems. A novel approach for preparing polyaniline (PANI) in FeCl₂/H₂O₂ system was developed. The PANI possessed an excellent dispensability. Corrosion protection of epoxy coatings containing two kinds of polyaniline (PANI) on Q235 steel was studied by electrochemical impendance spectroscopy (EIS) technique and Tafel polarization test in 3.5 wt% sodium chloride (NaCl) aqueous solution. The results indicated that the epoxy coating containing PANI obtained in FeCl₂/H₂O₂ system had the best performance of the corrosion protection among three systems under investigation. The possible protective mechanism of PANI was discussed.     

Preparation of polyaniline–TiO2 composite and its comparative corrosion protection performance with polyaniline

Due to strict environmental regulations on the usage of chromate in the coating industries, search for effective inhibitive pigment in replacing those chromate pigments has become necessary. In recent years it has been shown that electrically conducting polymers such as polyaniline (PANI) incorporated coatings are able to protect steel due to their passivating ability similar to that of chromates. This work presents the comparative corrosion protection performance of the coatings containing polyaniline and polyaniline–TiO₂ composite (PTC) on steel in acrylic binder. The PANI and PTC were prepared by chemical oxidative method of aniline by ammonium persulfate. The polymers were characterized by FTIR, XRD and SEM. The corrosion protection performance of the coatings containing PANI and PTC on steel was evaluated by immersion test in 3% NaCl for 60 days and salt fog test for 35 days. The performance of the coatings in both the tests was investigated by open circuit potential measurements and EIS technique. It has been found that the open circuit potential values of PTC containing coating are more nobler by 50–200 mV in comparison to that of coatings with PANI. Besides, the resistance values of the coating containing PTC were more than 10⁷ Ω cm² in the 3% NaCl immersion test after 60 days and 10⁹ Ω cm² in the salt fog test of 35 days which were two orders high in comparison to that of PANI containing coatings. The better performance of PTC containing coatings may be due to uniform distribution of polyaniline which can form uniform passive film on the iron surface.     

Effect of Aspergillus niger Tiegh. L-10 on the physical and chemical properties of a polyaniline coating in the growth substrate

The influence of the growth of Aspergillus niger Tiegh. fungi on the morphological, chemical and electrochemical properties of the polyaniline (PANI) modified Ni surface has been investigated. The strain of Aspergillus niger Tiegh. L-10 was cultivated on the malt extract agar (DIFCO OXOID). A PANI film was synthesized by potentiodynamic polymerization in an aqueous 0.3 M H₂C₂O₄ solution containing 0.1 M aniline on the Ni electrode. The electrochemical behaviour of polymer films was determined in a 0.05 M H₂SO₄ solution by the cyclic voltammetry method. The composition of PANI and Aspergillus niger Tiegh. treated PANI surfaces have been characterized using X-ray photoelectron spectroscopy (XPS). The morphology has been studied using scanning electron microscopy (SEM). The attachment of a polymer film via the metabolic product resulted in oxidation of the surface. It was estimated that at the PANI/microorganism interface, a Ca-complexed carboxylate interfacial reaction product was formed.     

Electrochemical synthesis and corrosion behavior of poly(N-ethyl aniline) coatings on Al-2024 alloy

Poly(N-ethyl aniline) coating was electrodeposited onto Al-2024 by using cyclic voltammetry. The coating was characterized by infrared spectroscopy, cyclic voltammetry and UV-Vis spectroscopy. The corrosion resistance of the film was evaluated by dc polarization studies. These coatings were formed in aqueous solution of oxalic acid. The concentration of monomer and oxalic acid were kept constant at 0.1 and 0.3 M, respectively. The formation of the polymer coating was monitored by cyclic voltammetry and infrared spectroscopy. Preliminary dc polarization results show that poly(N-ethyl aniline) has a corrosion rate of about 0.004 mmpy, which is significantly lower (about one order of magnitude) than that for the non-coated Al-2024.     

Properties of electropolymerised polyaniline thin films obtained from different supporting electrolytes

This work reports on the properties of polyaniline (PANI) films electrochemically synthesised onto indium tin oxide (ITO) coated glass substrate from a mixed solution of 0.1?M aniline with three different types of supporting electrolytes: HNO₃, H₂SO₄ and H₃PO₄. In order to investigate the effect of dopant on the behaviour of polyaniline different techniques have been employed. These characterisations were made using photoelectrochemical, FTIR and Raman spectroscopies, field-emission scanning electron microscopy, UV–vis spectroscopy, diffuse reflectance spectrophotometry and photoluminescence techniques. The potocurent transients show a change of PANI films conductivity from p-type to n-type by changing the supporting electrolytes. The FTIR technique and Raman spectroscopy confirmed the formation of PANI thin film on ITO substrates. The morphology of the electropolymerised PANI thin films is closely related to the supporting electrolytes. Compact and spongy morphologies were observed for PANI films deposited in different supporting electrolytes. The optical measurements show an optical transmittance in the visible region, with variations depending on the nature of electrolytes.     

Electro-Synthesis of Nano-Colloidal PANI/ND Composite for Enhancement of Corrosion-Protection Effect of PANI Coatings

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was prepared 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. The corrosion performance of the coatings was investigated in 0.5 M H₂SO₄ solution by electrochemical impedance spectroscopy and polarization methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in 0.5 M H₂SO₄ corrosive medium. X-ray diffraction and FT-IR techniques confirmed the intercalation of the nanoparticles in PANI matrix.     

Corrosion inhibition of aluminum alloy in chloride mediums by undoped and doped forms of polyaniline

Corrosion inhibition of Al 3003 alloy by pure undoped PANI (emeraldine base) and PANI doped with p-toluene-sulfonic, camphorsulfonic and dodecylbenzenesulfonic acids was investigated. Corrosion resisting properties of PANI coatings with an artificially created hole defect were evaluated by electrochemical impedance spectroscopy (EIS) in aqueous 3.5% NaCl and 0.1 N HCl solutions. The highest corrosion inhibition factor was obtained for undoped PANI being equal to 12 and 4.4 in neutral and acidic media, respectively. The results indicated that corrosion protection of the bare aluminum alloy surface resulting from a defect of the PANI coating is in line with an increase of the thickness of the oxide layer protecting the aluminum alloy surface. The efficiency of corrosion protection of mild steel and aluminum alloy by polyaniline coatings was compared.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

Poly(N-methylaniline) coatings on stainless steel by electropolymerization

Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion.     

Synthesis of polyaniline nanotubes using Mn2O3 nanofibers as oxidant and their ammonia sensing properties

In this work, a new method for the synthesis of polyaniline (PANI) nanotubes was presented. Experimentally, Mn₂O₃ nanofibers prepared by electrospinning technique were used as the oxidant template to initiate the polymerization of aniline in acid solution. After reaction, polyaniline shells were formed on the Mn₂O₃ nanofiber surface, and the Mn₂O₃ nanofibers were spontaneously removed. As a result, PANI nanotubes were obtained. As-prepared PANI nanotubes show an average diameter of 80 nm and inner diameter of 38 nm. The final PANI nanotubes were characterized by SEM, EDX, TEM, FTIR and XRD. The gas sensing of as-obtained PANI nanotubes was also investigated. It was found that the PANI nanotube sensing device could detect as low as 25 ppb NH₃ in air at room temperature with good reversibility.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped conductive fibers based on polyaniline and polyacrylonitrile

Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirring with magnetic bar. This research was conducted to investigate conducting fibers of polyaniline:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with 5 mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electrical conductivity with different type doping agents (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

Anticorrosive properties with catalytic behaviour of primer PANI film and top PPy coating synthesised in presence of novel norephedrine based amino alcohol compound

Polyaniline film as primer coating was deposited on stainless steel (SS) in aniline containing aqueous oxalic acid solution, and subsequent synthesis of top PPy film with 2-((5-ethylthiophen-2-yl) methylamino)-1-phenylpropan-1-ol (AAN) compound of different concentrations was achieved in acetonitrile-LiClO₄ successfully. The corrosion performances of coated and uncoated electrodes in 3·5%NaCl solution were evaluated with the help of AC impedance spectroscopy, anodic polarisation plots and open circuit potential time curves. The protective effect of bilayer coatings with AAN compound on SS electrode grew in parallel with extended exposure time. The regular increase in the charge transfer resistance of SS/PANI/PPy-AAN17 electrode was attributed to allowing the limited ion diffusion of top PPy coating with AAN17 compound. The high 21764 Ω s^?1/2 value of the Warburg coefficient showed that PPy-AAN17 film on the SS/PANI coating led to the formation of protective oxide layers due to the catalytic behaviour of PANI film.     

Synthesis and properties of high performance nanostructured polyaniline: Effect of initiator dosage and molecular oxygen

The effects of ammonium persulfate (APS)/aniline feed molar ratio or O₂ bubbling on the polymerization of polyaniline (PANI) in self-stabilized dispersion polymerization (SSDP) were examined. As the APS/aniline feed molar ratio was increased from 0.25/1.00 to 1.50/2.00, the polymerization yield was enhanced from 20% to 80%. However the molecular weight reduction with increased feed ratio, that is normally observed when PANI was polymerized in aqueous medium, was little. The O₂ bubbling during polymerization made the nanostructure of PANI to be finer, and this improved the solubility of PANI in solvent. The FT-IR spectra showed that the PANI prepared by SSDP, which have high conductivity in the range of 600–800 S/cm, contained less amount of the structures by ortho-coupling or Michael reductive addition of aniline compared to that synthesized by the standard method in an aqueous medium.     

Polyaniline microtubes synthesized via supercritical CO2 and aqueous interfacial polymerization

We report a new route to prepare polyaniline (PANI) microtubes via supercritical (SC) CO₂/aqueous interfacial polymerization. The synthesis is based on the well-known chemical oxidative polymerization of aniline in an acidic environment, with ammonium peroxydisufate (APS) as the oxidant, and sodium dodecyl sulfate (SDS) surfactant was used as the template. The main feature of this route is that the monomer (aniline) which is dissolved in SC CO₂ phase, slowly polymerized at the interface of SC CO₂ and aqueous solution to form the PANI microtubes. The morphologies, phase structure, composition and some properties of PANI microtubes were characterized by TEM, SEM, XRD, IR, XPS UV–vis and SYSTEM DM digital multimeter, respectively.     

Redox behaviour of polyaniline–palladium catalytic system in the presence of formic acid

Redox behaviour of polyaniline (PANI) films containing chemically incorporated palladium particles in the presence of formic acid was studied. Two types of PANI–Pd hybrids were prepared: PANI-PdHA and PANI-PdLA, depending on the acidity of the PdCl₂ solution used for the introduction of palladium into the polymer matrix. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the nature of processes involved upon the decomposition of formic acid on polyaniline–palladium hybrids. In particular, UV–vis changes of both kinds of films were followed in situ (in 1 M aqueous HCOOH solution) as a function of time. Rather unexpectedly, the redox properties of polyaniline films are found to be significantly altered in the presence of palladium particles. Particles of Pd⁰ promote the reduction of PANI from the most oxidized and semi-oxidized states to the most reduced one with simultaneous decomposition of formic acid.