Electropolymerization of poly(N-ethyl aniline) on mild steel: Synthesis, characterization and corrosion protection

Poly(N-ethylaniline) (PNEA) coatings on the mild steel electrode were synthesized by electrochemical oxidation of N-ethylaniline using aqueous oxalic acid solutions as reaction medium. Electrodeposition was carried out by potentiodynamic, potentiostatic and galvanostatic synthesis techniques. Smooth, adhesive and thick PNEA coatings on mild steel could be electrosynthesized during sequential scanning of the potential region between −0.5 and 1.4 V versus SCE, with scan rate of 20 mV s⁻¹. The electrodeposited coatings were characterized by cyclic voltammetry, FT-IR and UV-vis techniques. Corrosion behavior of PNEA coated steels was investigated by linear anodic potentiodynamic polarization technique and Tafel test. Anodic potentiodynamic polarization results showed that electrodissolution current value of PNEA coated steel decreased about 90% compared to that of the uncoated steel in 0.5 M H₂SO₄ aqueous solution. Tafel plots showed also strong decrease of corrosion current for the PNEA coated electrode compared to the uncoated steel electrode in 3% NaCl as corrosive medium.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Electropolymerization, characterization and corrosion performance of poly(N-ethylaniline) on copper

Poly(N-ethylaniline) (PNEA) coatings were grown by cyclic voltammetry technique on copper from 0.1 M N-ethylaniline (NEA) in 0.3 M oxalic acid solution. The optimum conditions (e.g. upper potential limit, scan rate and cycle number) effect on corrosion performance of synthesized PNEA films were determined in order to obtain best protection results against corrosion. The electrodeposited coatings were characterized by cyclic voltammetry (CV), Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) spectroscopy and scanning electron microscopy (SEM). Redox parameters were found after electrochemical tests and results of stability tests of these films impart an electroactive behavior that is composed of both diffusion control and thin film behavior. In addition, corrosion performance of PNEA coatings were investigated in 0.1 M H₂SO₄ by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) techniques.     

Poly(N-ethylaniline) coatings on 304 stainless steel for corrosion protection in aqueous HCl and NaCl solutions

Poly(N-ethylaniline) (PNEA) coatings were grown by potentiodynamic synthesis technique on 304 stainless steel (SS) alloy from 0.1 M of N-ethylaniline (NEA) in 0.3 M oxalic acid solution. Characterization of adhesive and electroactive PNEA coatings was carried out by cyclic voltammetry, FT-IR spectroscopy and scanning electron microscopy (SEM) techniques. The protective properties of PNEA coatings on SS were elucidated using linear anodic potentiodynamic polarization, Tafel and electrochemical impedance spectroscopy (EIS) test techniques, in highly aggressive 0.5 M HCl and 0.5 M NaCl solutions. Linear anodic potentiodynamic polarization test results proved that PNEA coating improved the degree of protection against pitting corrosion in HCl and NaCl solutions. Tafel test results showed that PNEA coating appears to enhancement protection for SS in 0.5 M NaCl and 0.5 M HCl solutions. However, according to long-term EIS results, PNEA coating is better for the protection of SS electrodes during the long immersion period in NaCl compared to that in HCl medium.     

Electrosynthesis of PAni/PPy coatings doped by phosphotungstate on mild steel and their corrosion resistances

Polyaniline/polypyrrole (PAni/PPy), polyaniline-phosphotungstate/polypyrrole (PAni-PW₁₂/PPy) and PAni/PPy-PW₁₂ have been successfully electrodeposited on mild steel (MS) by cyclic voltammetry in aqueous oxalic acid solutions. It was found that the incorporation of PW₁₂ enhanced the corrosion resistance of PAni/PPy coating. Moreover, in comparison to PAni-PW₁₂/PPy, PAni/PPy-PW₁₂ coating exhibited better corrosion resistance for mild steel. After immersion of 36 h in 0.1 M HCl, for instance, the polarization resistance of PAni/PPy-PW₁₂ coating reached 1695 Ω cm², more than those of both PAni/PPy and PAni-PW₁₂/PPy.     

Dynamic light scattering studies on the aggregation behavior of tributyl phosphate and straight chain dialkyl amides during thorium extraction

Dynamic light scattering (DLS) studies were carried out to investigate the aggregation behavior of 1.1 M solutions of tributyl phosphate (TBP), N,N-dihexyl octanamide (DHOA) and of N,N-dihexyl decanamide (DHDA) in n-dodecane equilibrated with varying concentrations of nitric acid (0.1–6 M) and of Th (10–200 g/L). There was a gradual increase in thorium extraction with increased aqueous phase acidities. A significant enhancement in the aggregate sizes was observed with increasing concentration of thorium in the organic phase. The effect of 1-octanol as phase modifier was also investigated on the aggregation behavior of extracted species for TBP system.     

Corrosion inhibition effectiveness of zeolite ZSM-5 coating on mild steel against various organic acids and its antimicrobial activity

Zeolite ZSM-5 coating on mild steel had been assessed for its corrosion resistance property against organic acids, namely, acetic acid, formic acid and citric acid of varying concentrations at temperatures up to 60 °C under stagnant as well as stirred conditions by weight-loss and polarization methods. Biocidal activity of the zeolite coating against Gram-negative bacteria Escherichia coli, Pseudomonas putida, Salmonella typhi and Gram-positive bacteria Staphylococcus aureus by using minimum inhibitory concentration (MIC) was also studied. With zeolite coating, corrosion inhibition efficiency up to 98% was achieved for 6 h of duration of contact between coating and acid solutions. Similar resistance persisted for the duration of 7 days too. Results obtained showed that extent of corrosion of mild steel decreased in the order, formic acid > citric acid > acetic acid. Also as expected, corrosion resistance though only slightly, decreased with solution temperature and concentration. High anti-microbial activity was observed at very low values of MIC (100 μg/mL). In light of reported literature, the presence of the structure directing agent within the channels of the zeolite has been attributed for the high corrosion resistance as well as anti-microbial activity observed here. Thus, zeolite offers a “greener” alternate to chromium and epoxy polymers based corrosion resistance coating.     

Corrosion protection of new composite polymer coating for carbon steel in sulfuric acid medium by electrochemical methods

In this paper, electropolymerization technique has been used for the obtained of new composite: polypyrrole – dioctyl sulfosuccinate sodium/poly N-ethylaniline (PPY-AOT/PNEA) coatings over carbon steel of type OLC 45 electrode for anticorrosion protection. The PPY-AOT/PNEA coatings were successfully synthesized onto OLC 45 electrode by galvanostatic deposition from aqueous solutions 0.1 M NEA, 0.1 M PY, 0.01 M AOT and 0.3 M H₂C₂O₄ solution at different current densities (5, 3 and 1 mA/cm²) in different molar ratio. The anionic surfactant (AOT) as a dopant ion used during electropolymerization can have a significant result on the anticorrosion protection of the composite film by hindering the penetration of aggressive ions. The polymeric composite coatings have been analyzed by cyclic voltammetry (CV), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) methods. The corrosion resistance of PPY-AOT/PNEA coated carbon steel has been examined by potentiodynamic polarization techniques and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solutions. The data of the corrosion samples demonstrated that PPY-AOT/PNEA coatings assure a great anticorrosion protection of OLC 45 electrode in corrosive media. The corrosion rate of PPY-AOT/PNEA coated OLC 45 has been indicated to be ~9 times lower than of uncoated electrode. The corrosion protection effectiveness of the composite coating is more than 89%. The best efficiency is accomplished of PPY-AOT/PNEA obtained by electrodeposition at 5 mA/cm² current densities applied in molar ratio 5:1.     

The influence of pulse plating parameters on microstructure and properties of Ni-W-Si3N4 nanocomposite coatings

Nanosized silicon nitride (Si₃N₄) particles reinforced Nickel-tungsten composite coatings were deposited on the surface of C45 steel sheet by pulse electrodeposition. The effect of duty cycle, frequency, current pattern and presence of Si₃N₄ nanoparticles on microstructure, phases and corrosion resistance and mechanical properties of the coatings were investigated. The Si₃N₄ phase was incorporated into Ni-W alloy matrix uniformly and the inclusion content of in the coating was analyzed by energy dispersive x-ray spectrometer (EDS). The structure, microhardness and surface roughness of the coatings was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers micro-indenter and atomic force microscopy (AFM). The corrosion protection of steel by the coatings was evaluated by weight loss and electrochemical impedance spectroscopy (EIS). Corrosion rates of the coatings were determined using the Tafel polarization test. The results indicated that the duty cycle of 60%, pulse frequency of 1000 Hz, average current density of 5 A/dm⁻², and Si₃N₄ nanoparticles concentration of 30 g/L were the optimal plating conditions. The amount of Si₃N₄ particles incorporated into the coating that were produced under the optimum plating conditions was 2.1 wt%, and the microhardness was 1031 Hv as well as the crystallite size of this coating was 27 nm.     

Novel heterobimetallic Cu/Mn coordination polymers prepared by “direct permanganate” synthesis

Two heterometallic Cu/Mn complexes [Cu(Me₂en)₂][Mn₂(ox)₃] · 2H₂O (1) (Me₂en = N,N-dimethylethylenediamine, H₂ox – oxalic acid) and [Cu(1,3-pn)(ox)(H₂O)][Mn(ox)(H₂O)₂] · H₂O (2) (1,3-pn = 1,3-diaminopropane) are prepared by the one-pot reaction of copper powder, tetrabutylammonium permanganate, oxalic acid and N-chelating ligands. Their structures are investigated by single-crystal X-ray analysis that reveals interesting variation in bridging motives of the oxalate groups composing the Mn-polymeric fragments.     

Electrodeposition of poly(N-methylpyrrole) on stainless steel in the presence of sodium dodecylsulfate and its corrosion performance

Poly(N-methylpyrrole)-dodecylsulfate (PNMPy-DS) coating was electrosynthesized by potentiodynamic method on a stainless steel in oxalic acid solution containing sodium dodecylsulfate for the first time. The effects of electrochemical synthesis parameters, such as applied potential, scan rate and cycle number, on the protective behaviors of PNMPy-DS films were investigated and the optimum synthesis conditions were determined. The PNMPy-DS coating was characterized by the cyclic voltammetry, FT-IR spectroscopy and SEM methods. Corrosion protection behavior of this polymer-coated steel was investigated in 0.5 mol L⁻¹ HCl solution by potentiodynamic polarization and EIS methods. The results show that the PNMPy-DS coating provides effective protection for the stainless steel against to corrosion due to the fact that the large negatively charged dodecylsulfate dopant in the polymer structure electrostatically repels corrosive chloride ions and delays their access to metal surface.     

Assessment of soil washing for Zn contaminated soils using various washing solutions

Bench-scale soil washing experiments were conducted to remove Zn from contaminated soils. Various washing solutions including hydrochloric acid (HCl), nitric acid (HNO₃), sodium hydroxide (NaOH), oxalic acid (HOOCCOOH·2H₂O), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and tartaric acid (C₄H₆O₆) were used. The concentration of the washing solutions used in this study ranged from 0.1 M to 2 M with a liquid to solid ratio of 10. The soil washing results showed the following order of washing solution decreasing effectiveness for the removal of Zn: HCl > HNO₃ > H₂SO₄ > H₃PO₄ > C₄H₆O₆ > HOOCCOOH·2H₂O > NaOH.     

Electrochemical synthesis of poly(N-methylaniline) on an iron electrode and its corrosion performance

Synthesis of poly(N-methylaniline) (PNMA) on pure iron and Pt electrodes was carried out from aqueous 0.3 M oxalic acid solution containing 0.1 M N-methylaniline (NMA) by potentiodynamic and galvanostatic techniques. It was found that when compared to polyaniline (PAni) and its ring- and N-ethyl-substituted derivatives, PNMA can be electrosynthesized with lower upper scanning potential (upper potential limit, E_upp) of 0.8 V vs. saturated calomel electrode (SCE) on an Fe electrode. PNMA coatings were characterized by electrochemical, scanning electron microscopy (SEM) and FTIR techniques. Linear anodic potentiodynamic polarization results proved that increasing the acidity of the polymerization solution causes more effective protection against corrosion in 0.5 M H₂SO₄ medium for PNMA. Moreover, PNMA exhibited similar protective properties with PAni under the same corrosion test conditions. Tafel test results reveal that the PNMA coating appears to enhance protection for iron in 0.5 M NaCl and 0.1 M HCl solutions. According to EIS results, the PNMA coating is able to offer protection to Fe electrodes in NaCl compared to that in HCl medium over a long immersion period.     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.     

Selective boron extraction by polymer supported 2-hydroxylethylamino propylene glycol functions

Boron sorption ability of polymer supported 2-hydroxyethylamino propylene glycol functions was investigated. 2-hydroxyethylamino propylene glycol was prepared by reaction of glycidol with excess ethanolamine in N-methyl, 2-pyrrolidone (NMP). This was reacted with terpolymer of glycidyl metacrylate (0.4 mol) with methyl metacrylate (0.5 mol) and divinylbenzene (0.1 mol) which was prepared in spherical beads form (210–422 μm) by suspension polymerization.The resulting terpolymer having hydroxyethylamino propylene glycol functions (1.82 mmol g⁻¹) was found to be as efficient as previously reported iminodipropylene glycol functional resins in removal of trace boron from water. The resin showed a boron loading capacity of 1.6 mmol g⁻¹. Nearly second-order kinetics, with respect to the boric acid (k = 1.65 mol l⁻¹ s⁻¹, with a correlation factor of 0.99129) was determined in non-buffered conditions.It was observed that, more than 95% of boron is extracted by this resin from very dilute H₃BO₃ solution (100 ppm initial concentration) in less than 30 min of contact time. Splitting of sorbed boron can be achieved by simple acid leaching (4 M HCl) and regenerated by NaOH (0.1 M) solution.     

Polyaniline/polyacrylate core–shell composites: Preparation,morphology and anticorrosive properties

Polyaniline/partially phosphorylated poly(vinyl alcohol)/polyacrylate nanoparticles ((PAn/P-PVA)_x/PAc_y) were synthesized by encapsulation of varying amounts of PAn/P-PVA nanoparticles (x = 0.3, 0.5 or 0.7 g) with PAc (y = 4, 6 or 8 g acrylate monomers) via emulsifier-free emulsion polymerization. A monomer conversion level of 93.9% was achieved for the synthesis of the (PAn/P-PVA)_0.5/PAc₄ nanoparticles. X-ray diffraction analysis revealed that PAc was intercalated between the PAn/P-PVA layers, whilst transmission electron microscopy analysis of the different nanoparticles revealed they were spherical PAn/P-PVA agglomerates coated with PAc. Thermogravimetric analysis revealed that the thermal stability of the (PAn/P-PVA)/PAc nanoparticles decreased with increasing amounts of PAc. Cyclic voltammetry based analysis of the different (PAn/P-PVA)/PAc nanoparticles coated onto carbon fiber electrodes revealed that the PAn/P-PVA nanoparticles were encapsulated sufficiently by the non-conductive PAc and that the peak current decreased with increasing amounts of acrylate. With respect to the corrosion resistance in 1.0 M sulfuric acid, steel coated with the (PAn/P-PVA)_0.7/PAc₈ nanocomposite showed the best corrosion resistance (11.4%), but for the nanocomposites at each PAn/P-PVA loading level, the anticorrosive properties increased with increasing PAc levels, presumably due to the increasing tortuosity of the diffusion pathway through the coating for any corrosion agents.     

Electrochemical investigation of chromium nanocarbide coated Ti–6Al–4V and Co–Cr–Mo alloy substrates

This study investigated the electrochemical behavior of chromium nano-carbide cermet coating applied on Ti–6Al–4V and Co–Cr–Mo alloys for potential application as wear and corrosion resistant bearing surfaces. The cermet coating consisted of a highly heterogeneous combination of carbides embedded in a metal matrix. The main factors studied were the effect of substrate (Ti–6Al–4V vs. Co–Cr–Mo), solution conditions (physiological vs. 1 M H₂O₂ of pH 2), time of immersion (1 vs. 24 h) and post coating treatments (passivation and gamma sterilization). The coatings were produced with high velocity oxygen fuel (HVOF) thermal spray technique at atmospheric conditions to a thickness of 250 μm then ground and polished to a finished thickness of 100 μm and gamma sterilized. Native Ti–6Al–4V and Co–Cr–Mo alloys were used as controls. The corrosion behavior was evaluated using potentiodynamic polarization, mechanical abrasion and electrochemical impedance spectroscopy under physiologically representative test solution conditions (phosphate buffered saline, pH 7.4, 37 °C) as well as harsh corrosion environments (pH ～ 2, 1 M H₂O₂, T = 65 °C). Severe environmental conditions were used to assess how susceptible coatings are to conditions that derive from possible crevice-like environments, and the presence of inflammatory species like H₂O₂. SEM analysis was performed on the coating surface and cross-section. The results show that the corrosion current values of the coatings (0.4–4 μA/cm²) were in a range similar to Co–Cr–Mo alloy. The heterogeneous microstructure of the coating influenced the corrosion performance. It was observed that the coating impedances for all groups decreased significantly in aggressive environments compared with neutral and also dropped over exposure time. The low frequency impedances of coatings were lower than controls. Among the coated samples, passivated nanocarbide coating on Co–Cr–Mo alloy displayed the least corrosion resistance. However, all the coated materials demonstrated higher corrosion resistance to mechanical abrasion compared to the native alloys.     

Poly(N-ethyl-4-vinylpyridinium bromide)–sodium dodecyl sulfate complexes. Formation and supramolecular organization in salt containing aqueous solutions

Formation and supramolecular organization of poly(N-ethyl-4-vinylpyridinium bromide) (PEVP)–sodium dodecyl sulfate (SDS) complexes in aqueous-salt solutions have been studied. PEVP samples of three polymerization degrees (P_w = 570, 1200 and 2350) were used. For PEVP of lower polymerization degree (P_w = 570) only insoluble complexes were observed in the whole range of the reaction mixture composition studied: Z = [SDS]/[PEVP] ≤ 1. For PEVP of higher polymerization degrees (P_w = 1200 and 2350), water-soluble complexes are formed up to a critical value of the reaction mixture composition, Z, that is similar for both PEVP fractions. It was found that water-soluble complex species are either molecularly dispersed (i.e. each complex particle comprises only one macromolecule) or aggregated (includes about 40 polymer chains and 20,000 surfactant ions) depending on the complex composition. Complex composition, in its turn, was shown to be determined by PEVP polymerization degree and the reaction mixture composition.     

Adsorption performance of suitable nanostructured novel composite adsorbent of poly(N-methylaniline) for removal of heavy metal from aqueous solutions

Poly(N-methylaniline) (PNMA) composite composed of N-methylaniline and poly(ethanol) was prepared by in situ polymerization technique and characterized using FTIR, SEM-EDS and XRD instruments. Characterization of product revealed that this composite is crystalline in nature and the particles size is less than100 nm. The potential of this composite in removal of Cr(VI) ions from synthetic aqueous effluents was investigated by batch sorption system. The experimental results confirmed that this adsorbent has the potential application for removal of Cr(VI) ions from aqueous solution with the sorption capacity of 125 mg/g of Cr(VI)/0.1 g of adsorbent.     

Synthesis and swelling properties of poly[acrylamide-co-(crotonic acid)] superabsorbents

Superabsorbent polymers of acrylamide (AAm)/crotonic acid (CA) were synthesized by foamed polymerization in an aqueous solution of AAm with CA as a comonomer, initiated by an initiator couple of ammonium persulfate and N,N,N′N′-tetramethylethylenediamine. A crosslinking agent N,N′-methylenebisacrylamide, a foaming agent sodium bicarbonate, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The influences of the relative contents of CA, crosslinking agent, and initiator, on the swelling properties of the superabsorbent polymer systems were examined. The superabsorbent polymer synthesized with an AAm/CA ratio of 98:2 by mole, 0.5 wt.% of N,N′-methylenebisacrylamide and 1 wt.% of ammonium persulfate at 250 rpm and 50 °C for 30 min of polymerization time produced the highest water absorption of 211 ± 9 times its dried weight and could absorb water up to 162 ± 4 g g⁻¹ of the dry copolymer within 10 min. The electrochemical reaction for acrylamide–crotonic acid polymerization was investigated by cyclic voltammetry. The anodic current indicated that acrylamide acting as an electron donor whereas crotonic acid performed as an electron receiver, then providing the cathodic current. The diffusion of water into the superabsorbent polymer was non-Fickian (case II and anomalous). Acrylamide–crotonic acid superabsorbents containing various crosslinker concentrations had a water swelling in the range of 79–289 g g⁻¹. The diffusion coefficients varied between 6.9 × 10⁻⁹ and 5.1 × 10⁻⁸ cm² s⁻¹. Adsorption of the basic dye by the superabsorbent was a monolayer evaluated by the Langmuir isotherm. The superabsorbents can thus be used to adsorb cationic dyes in textile industry.