Effect of electrolyte and monomer concentration on anticorrosive properties of poly(N-methylaniline) and poly(N-ethylaniline) coated mild steel

The electrosynthesis of poly(N-methylaniline) (PNMA) and poly(N-ethylaniline) (PNEA) coatings on mild steel in aqueous oxalic acid solutions was carried out by potentiodynamic synthesis technique. The effects of monomer and electrolyte concentrations on electrochemical growth of PNMA and PNEA coatings on mild steel substrates were investigated. Repassivation peak did not appear during electrosynthesis of PNMA and PNEA coatings from solutions containing 0.1 M monomer and 0.1 M electrolyte. The tests for corrosion protection of the polymer coated and uncoated mild steel substrates were done in 3% NaCl solutions by dc polarization and electrochemical impedance spectroscopy (EIS) techniques. Corrosion tests revealed that PNMA and PNEA coatings exhibited effective anti-corrosive properties. The acidity of the polymerization solution was found to influence the anticorrosive behavior of the polymer coating.     

Effect of sulphate ion on the electrochemical polymerization of pyrrole and N-methylpyrrole

Pyrrole and N-methylpyrrole were electrochemically polymerized in an identical manner in aqueous electrolytes containing (Et₄N)BF₄, LiClO₄ or Na₂SO₄ to give films of the corresponding p-doped polymers. The polymer obtained from the aqueous Na₂SO₄ electrolyte, [(poly N-methylpyrrole)^+y (SO₄)_y/2^2-]_x, differed from the other polymers in that it exhibited a very low conductivity (≈ 10^?7 S/cm), contained a high concentration of > C=O groups and had an EPR linewidth, ΔH_pp, more than an order of magnitude greater than that found in the corresponding polymers obtained from the (Et₄N)BF₄ and LiClO₄ electrolytes. A sample of [(polyN-methypyrrole)^+y(BF₄)_y^?]_x electrochemically synthesized in CH₃CN and subsequently converted electrochemically to the corresponding sulphate in the Na₂SO₄ aqueous electrolyte exhibited normal behaviour. A mechanism is proposed for the introduction of > C=O groups into the poly(N-methylpyrrole) polymer during its electrochemical polymerization in the Na₂SO₄ aqueous electrolyte.     

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.     

Characterization of metal—oxide—semiconductor field-effect transistor (MOSFET) for polypyrrole and poly (N-alkylpyrrole)s prepared by electrochemical synthesis

In this study, films of the polypyrrole series, polypyrrole (PPy), poly(N-methylpyrrole) (PNMePy) and poly(N-ethylpyrrole) (PNEtPy), are prepared at room temperature by electrochemical polymerization of the corresponding monomer in acetonitrile, utilizing p-toluenesulfonic acid monohydrate (p-TSA) as a supporting electrolyte. The results show that the thermodecomposition temperature, interchain spacing, electrical conductivity and optical absorption peak wavelength decrease with an increase in the alkyl side chain length. On the other hand, the semiconductor characteristics of these conjugated conducting polymers are utilized in the metal—oxide—semiconductor field-effect transistor (MOSFET) fabrication by electrochemical synthesis. The MOSFETs of Au/p-TSA doped PPy (PNMePy, PNEtPy)/SiO₂/Si/Au exhibit ideal field-effect characteristics. The channel current, carrier mobility and transconductance of MOSFETs increase dramatically after adequate heat treatment. The carrier mobilities of the PPy and PNEtPy MOSFETs can reach about 1.7 cm² V⁻¹ s⁻¹, which is close to those of amorphous silicon inorganic transistors (0.1–1.0 cm² V⁻¹ s⁻¹ used extensively at present.     

Charge trapping in bilayers of conducting polymers under open circuit conditions: a protection of conducting polymer films from spontaneous charging/discharging

Spontaneous charging/discharging processes of polymers: polypyrrole and poly(N-methylpyrrole), doped with perchlorate (anion exchanging PPy and PMPy, respectively) and poly(4-styrenesulphonate) ions (cation exchanging PPy(PSS) and PMPy(PSS)) occurring in aqueous electrolyte solutions were studied using different electrochemical techniques. These reactions (oxidation of the polymer by dissolved oxygen and discharge of the polymer redox capacitance) are usually undesired processes leading to alteration of the charge accumulated in the polymer films. This paper points out that these processes can be significantly limited in polymer bilayers due to effect of charge trapping.     

Poly(N-methyl pyrrole) and its copolymer with pyrrole for mild steel protection

In this study, it was aimed to overcome disadvantages of polypyrrole films like water up taking and resulting low stability, via copolymerization of pyrrole and N-methyl pyrrole and preparing their bilayer films. Poly(N-methyl pyrrole) coating was synthesized electrochemically on mild steel and its corrosion performance has been investigated in 3.5% NaCl aqueous solution, by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential-time relation. This coating was found to have lower protection efficiency than single poly(pyrrole) coating. This case was related to weak adsorption behavior of poly(N-methyl pyrrole) film on mild steel. On the other hand, when this film was applied as a top coat on polypyrrole coated sample; the obtained coating system hindered the attack of corrosive environment and protected mild steel efficiently. The underlying poly(pyrrole) film was strongly adherent and the top poly(N-methyl pyrrole) coat improved barrier property by decreasing permeability and water mobility. Poly(pyrrole-co-N-methyl pyrrole) has also been synthesized from aqueous oxalic acid solutions containing various ratios of these two monomers. The copolymerization rate and protective behavior of copolymer were strongly affected by the monomer concentration ratio. The ratio of 1:3 (N-methyl pyrrole/pyrrole) gave the most protective copolymer coating and it exhibited better barrier property than single PPy. This was related to introduction of -CH₃ group which creates hydrophobic effect, when compared to -NH group of pyrrole unit. However, the solution with the ratio of 1:1 yielded a coating which had lower protection efficiency than single poly(pyrrole) film. This behavior was attributed to significant decrease in adsorption strength as the ratio of n-methyl pyrrole increased.     

Effects of electrochemical process parameters on the synthesis and properties of polypyrrole coatings on steel

Polypyrrole coatings have been successfully formed on low carbon steel by aqueous electrochemical process. The effects of electrochemical process parameters such as pH of the reaction medium, applied current density and initial monomer and electrolyte concentrations on the formation process of polypyrrole coatings were systematically investigated. The composition and morphology of the coatings were studied by FT-IR, elemental analysis and scanning electron microscopy (SEM). Our results show that passivation of the steel, electropolymerization of pyrrole, the morphology and properties of the coatings were all dependent on the electrochemical process parameters. By proper choice of the electrochemical process parameters, the passivation of the steel could be established within a short time and smooth, uniform, strongly adherent coatings could be formed on the steel substrate.     

In situ characterization of N-methylpyrrole and (N-methylpyrrole-cyclodextrin) polymers on gold electrodes in aqueous and nonaqueous solution

Electrosynthesized polymers of N-methylpyrrole (NMPy) and N-methylpyrrole-2,6-dimethyl-β-cyclodextrin NMPy-β-DMCD were characterized with cyclic voltammetry and in situ conductivity measurements in aqueous and nonaqueous solutions. In situ UV–vis-spectra of PNMPy and poly(NMPy-β-DMCD) films show differences both in band absorbances and in energies of polaronic transitions. For the electrosynthesis of poly(NMPy-β-DMCD), a (1:1) (mole–mole) NMPy-β-DMCD supramolecular cyclodextrin complex of N-methylpyrrole was used as starting material, which was previously characterized with proton NMR spectroscopy. The PNMPy and poly(NMPy-β-DMCD) films were prepared from 0.05 M NMPy and 0.05 M NMPy-β-DMCD complex, respectively, in 0.1 M LiClO₄ aqueous solution and 0.1 M LiClO₄ nonaqueous solution (acetonitrile) by electropolymerization. A slight positive shift of the oxidation peak and further differences are observed for poly(NMPy-β-DMCD) electrosynthesized in comparison with PNMPy prepared in both aqueous and nonaqueous solutions. Different CVs and ΔE_p of films were observed at various scan rates. In situ conductivity values of PNMPy and poly(NMPy-β-DMCD) films prepared in nonaqueous solution (acetonitrile) show higher values than with films prepared in aqueous solutions.     

FTIR study of chemically synthesized poly(N-methylpyrrole)

A FTIR study has been carried out on poly(N-methylpyrrole) chemically synthesized in water and in acetonitrile with 10% water. Conductivity of the polymer has been measured in pellets formed by pressing the powder obtained in the synthesis. The FTIR of the pellet is very different from that of the powder showing that there has been a pressure-induced conformational change. Evolution of the IR spectra with temperature shows that the polymer is stable up to 403 K and from that temperature conformational changes followed by decomposition of the polymer take place.     

Electropolymerization of N-methylanthranilic acid and spectroelectrochemical characterization of the formed film

The electropolymerization of N-methylanthranilic acid (NMAA) is reported in this paper. The monomer is substituted both at ortho- and N-position and, to the best of our knowledge, it has not been previously electropolymerized. Electropolymerization of NMAA was done on glassy carbon and optically transparent (indium) tin oxide electrodes. The obtained films, which are probably of an oligomeric nature (oligoNMMA), were characterized with cyclic voltammetry (CV), in situ UV–vis and Raman spectroscopy, ex situ FTIR spectroscopy and scanning electron microscopy (SEM).Our results show that NMAA can be electropolymerized as thin films in 1.0 M HClO₄, but the oxidation and reduction peak currents in the CVs indicate that the formed oligoNMAA films are thinner than poly(N-methylaniline) or poly(N-butylaniline) films prepared under similar conditions. The CV and UV–vis measurements confirm that oligoNMAA have three oxidation states like suggested in the redox scheme of substituted polyanilines. The Raman spectra of oligoNMAA also verify that more quinoid units are formed at higher potentials in accordance with the redox scheme. The ex situ FTIR measurement proves that covalently attached carboxylic acid groups are present in the film structure and attached to the oligoNMAA backbone.     

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.     

Electrochemical polymerization of o-anisidine on low carbon steel from aqueous salicylate solution: Corrosion protection study

The electrochemical polymerization of o-anisidine was carried out on low carbon steel from an aqueous salicylate medium using cyclic voltammetry. The resulting poly(o-anisidine) coatings were uniform and adherent to the steel substrates. These coatings were characterized by cyclic voltammetry, UV-visible absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction measurements and scanning electron microscopy. The ability of the poly(o-anisidine) coatings to protect low carbon steel in an aqueous 3% NaCl was evaluated by the potentiodynamic polarization measurements. The potentiodynamic polarization measurement reveals that the poly(o-anisidine) coating increases the corrosion potential and reduces the corrosion rate of low carbon steel almost by a factor of 15.     

Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium

In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (β _a) and cathodic (β _c) Tafel slopes, corrosion potential (E _corr), corrosion current density (i _corr), corrosion rate (CR) and polarization resistance (R _p), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks.     

Electrochemical synthesis of poly(para-phenylene) on platinum electrode in glacial acetic acid–sulfuric acid solvent

In concentrated sulfuric acid–glacial acetic acid solvent benzene is oxidized to poly(para-phenylene) (PPP) if the concentration of glacial acetic acid is less than 40 vol.%. Depending on the potential applied the chains containing 11–18 monomer units are formed. PPP forms quasi-reversible redox system, which is deactivated if oxidized at potentials greater than +1.35 V (vs SCE).     

Amperometric alcohol biosensors based on conducting polymers: Polypyrrole,poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxypyrrole)

Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, and l-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rak?) were determined with the sensors constructed. A good match with the chromatography results was observed.     

Corrosion and Wear Behaviors of Cr-Doped Diamond-Like Carbon Coatings

A combination of plasma-enhanced chemical vapor deposition and magnetron sputtering techniques has been employed to deposit chromium-doped diamond-like carbon (DLC) coatings on stainless steel, silicon and glass substrates. The concentrations of Cr in the coatings are varied by changing the parameters of the bipolar pulsed power supply and the argon/acetylene gas composition. The coatings have been studied for composition, morphology, surface nature, nanohardness, corrosion resistance and wear resistance properties. The changes in I _D /I _G ratio with Cr concentrations have been obtained from Raman spectroscopy studies. Ratio decreases with an increase in Cr concentration, and it has been found to increase at higher Cr concentration, indicating the disorder in the coating. Carbide is formed in Cr-doped DLC coatings as observed from XPS studies. There is a decrease in sp ³/sp ² ratios with an increase in Cr concentration, and it increases again at higher Cr concentration. Nanohardness studies show no clear dependence of hardness on Cr concentration. DLC coatings with lower Cr contents have demonstrated better corrosion resistance with better passive behavior in 3.5% NaCl solution, and corrosion potential is observed to move toward nobler (more positive) values. A low coefficient of friction (0.15) at different loads is observed from reciprocating wear studies. Lower wear volume is found at all loads on the Cr-doped DLC coatings. Wear mechanism changes from abrasive wear on the substrate to adhesive wear on the coating.     

Optimization of electrolyte concentration for surface modification of tantalum using plasma electrolytic nitridation

Plasma Electrolytic Nitriding (PEN) is a cathodic atmospheric plasma process which has shown a promising deposition of metal coatings that exhibits a significant adhesion to the substrate as well as high deposition rates. The structure of tantalum alloy, microhardness and corrosion resistance behavior after cathodic plasma electrolytic nitriding (PEN) in electrolyte containing urea and distilled water were investigated. An Optical microscope (OM), X-ray diffractometer and scanning electron microscopy (SEM) were used to characterize the phase composition of the modified layer and its surface morphology. The corrosion resistance properties of nitrided tantalum alloy are investigated. It was shown that various electrolytes provided metallic tantalum (Ta), TaN_0.43, TaN_0.1, Ta₄N, Ta₄N₅ and TaN phases and nitrogen solid solution in tantalum. The cathodic PEN with 78 wt% urea and 21.6 wt% distilled water had a microhardness of 1198.18 VHN, which was selected as the best sample in term of electrolyte composition.     

Electrooxidation of O-methoxyaniline as studied by electrochemical and SERS methods

The electrooxidation of o-methoxyaniline (o-MA) has been studied by electrochemical and surface-enhanced Raman scattering (SERS) methods. The electrochemical measurements showed that the early stages of o-MA electropolymerization were affected by both the monomer to acid concentration ratio and by the acid concentration. The SERS experiments demonstrated the C-N coupling mechanism of o-MA dimerization or oligomerization. The results of both methods indicate that the intermediate redox couple observed in electrochemical response of poly (o-methoxyaniline) can be assigned to the incorporated dimer probably having the cyclic structure.     

Poly (o-methoxy aniline): solubility,deprotonation-protonation process in solution and cast films

Solubility tests were performed at room temperature for poly (o-methoxyaniline) (POMA) inN,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), m-cresol, acetonitrile, chloroform, dichloromethane and xylene, and compared with those for polyaniline. A reversible solvatochromic transition from green to blue was observed in dilute POMA solutions in DMF, NMP and m-cresol indicating the occurrence of deprotonation-protonation processes. The solvent NMP more readily induced deprotonation processes at higher concentrations than those observed in DMF solutions. On the other hand, m-cresol exhibited an ability to protonate POMA in solution regardless of its undoped or doped state. Ultraviolet-visible spectra confirmed modifications of electronic transitions in agreement with the color changes. Correlations among crystalline properties, electron paramagmetic resonance results and electric conductivity of POMA films processed from DMF, NMP and m-cresol solutions are discussed.     

A.c. conductivity of poly(N-methylpyrrole)

The dielectric constant ɛ′(ω) and measured a.c. conductivity σ_m(ω) of lightly doped poly (N-methylpyrrole) films have been investigated in the temperature range 77–350 K and in the frequency range 100 Hz–1 MHz. In the low-temperature region the measured a.c. conductivity can be described by the relation σ(ω) = Aω_s, where the exponent s is found to be less than unity. At high temperatures the conductivity remains strongly frequency dependent but the dependence becomes weak at low frequencies. The temperature and frequency dependences of a.c. conductivity σ(ω) can be qualitatively explained by the contributions from two mechanisms, one giving rise to a broad dielectric loss peak having a distribution of relaxation times, and the other giving a linear dependence of conductivity on frequency.