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.     

Corrosion behavior study of AZ91 magnesium alloy coated with methyltriethoxysilane doped with cerium ions

The present work aims to investigate the corrosion behavior of AZ91 magnesium alloy treated with a 4% (v/v) methyltriethoxysilane (MTES) alcohol solution, with and without an alkaline pretreatment. The corrosion resistance was assessed by electrochemical impedance spectroscopy (EIS) and current densities were monitored by potentiodynamic polarization curves during immersion in a 0.1 M Na₂SO₄ solution. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to perform a surface analysis. The electrochemical results showed an improvement of anticorrosion properties of AZ91. Furthermore, alkaline pretreatment enhances adhesion between silane film and substrate surface. This can be attributed to a surface enrichment in hydroxyl groups after the alkaline step, which increases formation of Si–O–Mg covalent bonds. The addition of Ce(NO₃)₃ to the MTES bath was evaluated, and it was found that the electrochemical response depends on the cerium ions concentration used. It was shown that the addition of 6.0 × 10⁻⁵ M of Ce(NO₃)₃ to a MTES bath improves corrosion resistance. Higher concentration of cerium ions lead to destabilizing the siloxane network, decreasing the efficiency of the silane coatings.     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

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.     

Thermomechanical and corrosion inhibition properties of graphene/epoxy ester–siloxane–urea hybrid polymer nanocomposites

The effect of graphene on the corrosion inhibition properties of a hybrid epoxy–ester–siloxane–urea polymer was investigated. The weight fraction of graphene was varied from 1 to 2 wt%. Direct current polarization (DCP) and electrochemical impedance spectroscopic (EIS) techniques were used to measure the polarization and coating resistance of the coated aluminum alloy substrate. The grapheme/hybrid polymer composite coatings showed much higher corrosion inhibition property when compared to the neat hybrid polymer coating. An increase in glass transition temperature and rubbery region modulus was also observed for composites containing 1–2 wt.% of graphene. A direct correlation between the rubbery plateau modulus of free standing composite thin films and corrosion resistance of the composite coatings was made, indicating that the corrosion protection mechanism is due to restriction of the polymer chain motion by graphene which causes a decrease in coating permeability.     

Electroanalysis of ascorbic acid (vitamin C) using nano-ZnO/poly(luminol) hybrid film modified electrode

Electrochemical analysis of ascorbic acid (AsA) in physiological condition using a new hybrid film modified electrode is described. Electrochemical polymerization of luminol in 0.1 M H₂SO₄ solution was carried out using ZnO nanoparticles (ZnO-NPs) coated glassy carbon electrode (GCE) as working electrode. This hybrid film coated electrode noted as poly(luminol)/ZnO-NPs hybrid film modified GCE (PLu/ZnO-NPs/GCE). The atomic force microscope (AFM) and scanning electron microscope (SEM) studies were demonstrated that PLu/ZnO-NPs hybrid film covered the electrode surface and the ZnO-NPs particle sizes were <100 nm. The visible blue colored organic–inorganic (PLu/ZnO-NPs) hybrid films were observed on the electrode surface. Electrochemical studies proved that PLu/ZnO-NPs hybrid film modified electrode is electroactive in the pH range from 1 to 11 and the poly(luminol) (PLu) redox peak was pH dependent with a slope of ?53 mV/pH. The PLu/ZnO-NPs modified electrodes electroactivity also investigated by catalyzing the oxidation of AsA, demonstrating its great potential applications in electroanalysis of AsA. The resulting, AsA electrochemical sensor exhibited a wide linear response range (from 1 × 10^?6 to 3.6 × 10^?4 M, r² = 0.9989), lower detection limit (1 × 10^?6 M) and fast response time (3 s) for AsA determination. Our results show that PLu/ZnO-NPs hybrid film provides a novel and efficient platform for the oxidation of AsA and realizing efficient electrocatalysis and that the materials have potential applications in the fabrication of electrochemical sensors. Analysis of commercial vitamin C samples using PLu/ZnO-NPs hybrid film modified electrode was demonstrated and the obtained results are good agreement with the labeled amount.     

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.     

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.     

Assessment of a one-step intelligent self-healing vanadia protective coatings for magnesium alloys in corrosive media

Eco-friendly vanadia based chemical conversion coating was applied for improving the corrosion resistance of a newly developed magnesium AZ31 HP-O alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) and pH on the corrosion protection performance of magnesium substrate were investigated. EIS and cyclic voltammetry techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. Results showed a marked increase in the localized corrosion resistance after applying vanadia surface treatment of 50 g/l as measured by EIS and polarization techniques. The optimum conditions to obtain protective coatings for AZ31 HP-O were determined. The surface morphology, composition and microstructure of conversion coatings were followed by AFM, SEM-EDS and macroscopic imaging techniques.     

Wear-corrosion behavior of ultra-thin diamond-like carbon nitride films on aluminum alloy

Diamond-like carbon films exhibit high hardness, high wear resistance and a low friction coefficient. They are extensively utilized in the mechanical, electronic and biomedical industries. This work evaluates the effect of the thickness of ultra-thin diamond-like carbon nitride films on their corrosion properties and their wear-corrosion resistance in a mixed 1 M NaCl + 1 M H₂SO₄ solution using electrochemical methods. The corrosion current density and weight loss of all films during and after wear-corrosion test are also recorded. This work employs ion beam-assisted deposition (IBAD) to deposit DLC nitride films of various thicknesses (1.5, 2.0, 2.5 and 3.0 nm), containing 60% nitrogen gas in the form of a gaseous mixture of C₂H₂ + 60%N₂. The thickness of the films was measured using a transmission electron microscope (TEM). The atomic bonding structures of these DLC nitride films are analyzed using a Raman spectrometer and by electron spectroscopy for chemical analysis (ESCA). A scanning electron microscope (SEM) was adopted to elucidate the surface morphologies of the specimens after corrosion and wear-corrosion. The results indicated that all of the nitrogen-containing DLC films excellently protected the 5088 Al–Mg alloy substrate with an electroless plated Ni–P interlayer against corrosion, and that the degree of protection increases with the thickness of the film. In the wear-corrosion tests various potentials were applied during wear in the particular corrosive solution. The results further demonstrated that the wear-corrosion resistance of all the nitrogen-containing DLC films was as effective as corrosion protection, and that the wear-corrosion loss decreased as the film thickness increased.     

Impedance characterization of the electrochemical environment under a polymer film artificially delaminated

Knowledge of the electrical conductivity of the zone under a delaminated paint film is one necessary input parameter for the simulation of electrochemically driven underpaint corrosion. In this work, a microelectrode array system has been developed, tested, and applied to measure the spatial distribution of resistivity in the delaminated zone along the metal/polymer interface. The experimental device consists of a linear array of six 100 μm diameter stainless steel microelectrodes (100 μm in diameter) embedded in a steel substrate. A polymer coating was applied and an artificial “delaminated zone” was created using the laser-induced decohesion technique. The electrochemical impedance was measured between the first uncovered electrode and the electrodes at progressively increasing distances in the artificial delaminated zone. A steady decrease in the impedance with time can be observed, probably due to the continued ingress of electrolyte and a variation of the gap width.     

The effect of SCMs on the corrosion of rebar embedded in mortars subjected to an acetic acid attack

Agricultural effluents are transformed under bacteria effect into organic acids which constitute severe chemical and electrochemical attacks for the reinforced concrete of agricultural structures. Among supplementary cementing materials (SCMs), blast-furnace slag (GBFS) and metakaolin (MK) are classified chemically resistant to the aggressiveness of acidic media and especially organic acids. The objective of this research was to evaluate the effect of GBFS and MK on the corrosion performance of reinforced mortars. Here, electrochemical measurements allow determining the time needed to initiate the corrosion. Mortar cylinders were made with three cement types including ordinary Portland cement (OPC), GBFS and MK cements at a fixed water/cementitious material (w/cm) ratio of 0.65. Corrosion of rebars was simulated by subjecting cylinder specimens to cyclic loading with acetic acid solution (pH 4, 0.5 M) and drying. Concrete resistivity and reinforcing steel potentials were measured up to 429 days of age. At the end of the experiment, all specimens were saw cut split open, and visually inspected. It was found that the drop in the linear polarization resistance and corrosion potential curves reflect the time needed to initiate the corrosion. Blending the cement with 20% of MK is beneficial with regard to delaying the onset of the corrosion by a factor of more than two. However, using high percentage of GBFS (80%) decreases the time to initiate the corrosion for specimen subjected to acetic acid attack.     

Electrochemical preparation and characterization of nickel and zinc-modified poly-2-aminothiazole films on mild steel surface and their corrosion inhibition performance

Poly-2-aminothiazole (pAT) was electrochemically synthesized on a mild steel (MS) specimen from 0.3 M aqueous ammonium oxalate solution containing 0.01 M 2-aminothiazole (2-AT) using cyclic voltammetry technique. The synthesized polymer film was then modified by electrodeposition of 100 μg cm⁻² Ni (MS/pAT–Ni) and Zn (MS/pAT–Zn) on top of the polymer surface. The surface morphologies of the polymer films were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental analysis of the surface films was performed by energy dispersive X-ray spectroscopy (EDX). The effectiveness of the coatings in preventing corrosion of MS in 3.5% NaCl solution was assessed using electrochemical techniques. It was found that the obtained coatings were adherent to the steel surface. The pAT film provided a good corrosion protection against the attack of corrosive environment. Moreover, the modification of pAT film by deposition of Ni and Zn on top of the polymer surface significantly enhances the corrosion protection performance of the polymer film by exhibiting an improved barrier effect against the attack of corrosive environment. The surface morphologies and protection ability of the layers were found to be dependent on the type of deposited metal.     

The application of polycarbazole,polycarbazole/nanoclay and polycarbazole/Zn-nanoparticles as a corrosion inhibition for SS304 in saltwater

Polycarbazole (PCz), polycarbazole/nanoclay and polycarbazole/Zn-nanocomposites were chemically and electrochemically synthesized on a stainless steel (SS304) electrode. The modified electrodes were characterized by electrochemical methods (CV and chronoamperometry), Fourier transform infrared spectroscopy (FTIR)-attenuated transmission reflectance (ATR), scanning electron microscopy (SEM)-energy dispersive X-ray analysis (EDX), four point probe, electrochemical impedance spectroscopy (EIS), and equivalent circuit model of R_s(Q_c(R_c(Q_pR_ct))). The electrochemical behavior of the modified films on SS304 was assessed by open circuit potential monitoring, potentiodynamic polarization and EIS measurements to test the corrosion protection efficiency against 3.5% NaCl solution. PCz, PCz/nanoclay and PCz/nanoZn films obtained by chemical method coated on SS304 electrode exhibited better corrosion protection performance compared to the films obtained by the electrochemical method. This result may be attributed to the effective formation of a thin and protective layer. The highest protection efficiency (PE = 99.81%) was obtained for chemically synthesized PCz films.     

Electrochemical synthesis and characterization of a novel thiazole-based copolymer and its application in biosensor

A novel copolymer based on 2-aminothiazole (AT) and 2-amino-4-thiazoleacetic acid (ATA) is electrochemically synthesized and then characterized using UV–visible absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and electrochemical techniques. The results confirmed that the obtained polymer was a copolymer rather than a blend or a composite of the respective homopolymers and could improve the electrochemical response of both positively and negatively charged analytes. Therefore, the copolythiazole film was applied to determine ascorbic acid (AA), dopamine (DA) and uric acid (UA). It is found that the peak separating degrees and peak currents of AA, DA and UA at copolythiazole modified electrode were much better than those at bare GCE. Under the optimum conditions, the linear calibration curves were obtained in the range of 10–2000 μM for AA, 1–150 μM for DA, 1–180 μM for UA. The detection limits of AA, DA and UA were 2, 0.04 and 0.4 μM, respectively (S/N = 3). The practical application of the modified electrode was demonstrated by the determination of UA in urine sample.     

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.     

Plant derived cationic dye as an effective corrosion inhibitor for 7075 aluminum alloy in 3.5% NaCl solution

The inhibition of the corrosion of 7075 aluminum alloy in 3.5 wt.% NaCl solution by 5,6-dihydro-9,10-dimethoxybenzo[g]-1,3-benzodioxolo[5,6-a]quinolizinium (berberine) has been studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM). Inhibition efficiency was found to increase with increasing concentration of berberine. The adsorption of the berberine on the 7075 aluminum alloy surface obeyed the Langmuir adsorption isotherm. The adsorbed film on 7075 aluminum alloy surface containing inhibitor was confirmed by the SEM, and SECM. The results obtained showed that the berberine could serve as an effective inhibitor of the corrosion of 7075 aluminum alloy in 3.5% NaCl.     

Performance of EP/PpPDA and EP/PpPDA/SiO2 nanocomposite on corrosion inhibition of steel in hydrochloric acid solution

Epoxy-poly p-phenylendiamine (EP/PpPDA) and its nanocomposite with SiO₂ nanoparticles (EP/PpPDA/SiO₂) were synthesized and tested as potential corrosion inhibitors of steel in 1 M HCl solution. Performance of EP/PpPDA/SiO₂ and EP/PpPDA coatings on protection of steel against corrosion was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Atomic force microscopy (AFM) and at various temperatures between 298 and 328 K. Changes in the coating resistance and charge-transfer resistance with temperature were analyzed to determine the activation energies of the processes involved. The determined values of activation energy showed that the EP/PpPDA/SiO₂ coating has better anti-corrosion effect than EP/PpPDA. The thermodynamic functions of dissolution processes were also calculated and discussed. The results from AFM observations indicated that the presence of SiO₂ nanoparticles increased the roughness of Epoxy-poly p-phenylendiamine/SiO₂ nanocomposite (EP/PpPDA/SiO₂). It was finally concluded that the presence of silica nanoparticles enhance the protection properties of EP/PpPDA coating as a novel potential corrosion inhibitor for steel.     

Recognition of dimethoate carried by bi-layer electrodeposition of silver nanoparticles and imprinted poly-o-phenylenediamine

Thin film of a molecular imprinted polymer based on electropolymerization method with sensitive and selective binding sites for dimethoate was developed. This film was cast on gold electrode by electrochemical polymerization in solution of o-phenylenediamine and template dimethoate via cyclic voltammetry scans and further deposition of Ag nanoparticles. The surface plasmon resonance and cyclic voltammetric signals were also recorded simultaneously during the electropolymerization, controlling the thickness of the polymer film to be 25 nm. The imprinted film showed high selectivity towards to dimethoate. The recognition between the imprinted sensor and target molecule was observed by measuring the variation amperometric response of the oxidation–reduction probe, K₃Fe(CN)₆, on electrode. Under the optimal experimental conditions, the peak currents were proportional to the concentrations of dimethoate in two ranges, from 1.0 to 1000 ng mL^?1 and from 1.0 to 50 μg mL^?1, with the detection limit of 0.5 ng mL^?1. Due to the high affinity, selectivity and stability the imprinted sensor provides a simple detection platform for organophosphate compounds.     

The effect of temperature and hydrodynamics on carbon steel corrosion and its inhibition in oxygenated acid–salt solution

Corrosion of carbon steel in hydrochloric acid (HCl)–sodium sulphate (Na₂SO₄) solution mixture was investigated using rotating cylinder electrode (RCE) for a range of rotation velocity, 0–2000 rpm, solution temperature of 32–52 °C, and different oxygen concentrations. The corrosion rat was determined by using both weight loss method and electrochemical polarization technique. Different acid and salt concentrations were used ranged from 0.01 to 0.2 M for salt and 0.5 to 5% for acid. The conjoint effect of increased oxygen concentration and high rotational velocity was studied based on experimental measurements of O₂ concentration. The effects of operating conditions on indole and cetyl trimethyl ammonium bromides (CTAB) inhibition efficiency were also studied and discussed. The results showed that increasing the rotational velocity leads to an increase in the corrosion rate depending on the concentration of salt and acid. Increasing the temperature and acid concentrations leads to an increase in the corrosion rate while the corrosion rate exhibited unstable trend with salt concentration leads to change of corrosion. It is found that increasing O₂ concentration leads to a considerable increase in the corrosion rates especially at high rotational velocity. Indole and CTAB inhibitors exhibited very good inhibition efficiency in most conditions investigated with the former exhibited better inhibition efficiency arriving up to 87% at low rotational velocities. The inhibition efficiency of both inhibitors was found to decrease with increasing velocity. In addition, indole inhibitor reveals excellent inhibition efficiency even at high temperatures while CTAB efficiency decreased appreciably with temperature increase.