Corrosion protection of steel by polyaniline blended coating

Phosphate doped polyaniline was synthesized from aqueous phosphoric acid containing aniline by chemical oxidation method using ammonium persulphate as oxidant. The polymer was characterized by UV–vis and FT-IR spectroscopic techniques. Using this polymer, a paint with 1% polyaniline was prepared with epoxy binder. The corrosion resistant property of the polymer containing coating on steel was found out by open circuit potential measurements and electrochemical impedance spectroscopic method in 0.1 N HCl, 0.1 N H₃PO₄ and 3% NaCl for a duration of 50 days. The coating was able to protect the steel more in 0.1 N H₃PO₄ and 3% NaCl media than in 0.1 N HCl.     

Improvement of corrosion protection offered to galvanized steel by incorporation of lanthanide modified nanoclays in silane layer

Silane sol–gel based films are very promising alternatives to the traditional chromate pre-treatments. However, the protection offered by the silane films strongly decreases when the coating is damaged. Some previous studies showed that the barrier properties of the silane layer can be improved by incorporation of clay nanoparticles. Moreover, inhibitive metallic cations can be incorporated in the nanoclays by ion exchange, providing a way to prepare cheap corrosion inhibitors nanoreservoirs offering self-healing properties. Rare earth (RE) metal salts have been shown to be effective corrosion inhibitors on a wide range of metals, including hot dip galvanized (HDG) steel. For this study, montmorillonite clay is modified to obtain a Ce(III) montmorillonite clay (Ce-MMT). The amount of incorporated Ce(III) is characterized by means of XRF measurements. X-ray diffraction showed that the Ce(III) is located in the interlayer space.     

Inhibition of mild steel corrosion in the presence of fatty acid triazoles

The influence of some fatty acid triazoles namely, 4-Phenyl-5-undecyl-4H- [1,2,4] triazole-3-thiol (PUTT), 5-Heptadec-8-enyl-4-phenyl-4H- [1,2,4] triazole-3-thiol (HPTT), and 5-Dec-9-enyl-4-phenyl-4H- [1,2,4] triazole-3-thiol (DPTT) on the corrosion of mild steel in 1 M hydrochloric acid (HCl) and 0.5 M sulfuric acid (H₂SO₄) was studied by weight loss and potentiodynamic polarization methods. The values of activation energy and free energy of adsorption of all the triazoles were calculated to investigate the mechanism of corrosion inhibition. The potentiodynamic polarization studies were carried out at room temperature, according to which all the compounds were mixed type inhibitors and inhibit the corrosion of mild steel by blocking the active sites of the metal. The adsorption of all the triazoles on mild steel surface in both the acid solutions was found to obey the Langmuir adsorption isotherm. All the compounds showed good inhibition efficiency in both acids. The inhibition efficiency of the compounds was found to vary with their nature and concentration, solution temperature and immersion time. Electrochemical impedance spectroscopy was also used to investigate the mechanism of the corrosion inhibition.     

Coatings based on electronic conducting polymers for corrosion protection of metals

In this work, corrosion protection of mild steel by a novel epoxy resin (EP)-based coating system containing polyaniline (PAni) as an anticorrosive agent was studied. The corrosion behavior of mild steel samples coated with an EP/PAni-EB (emeraldine base), EP/PAni-ES (emeraldine salt), EP/SPAN (PAni sulfonated), EP/PAni-fibers, EP/PhoZn (zinc phosphate), EP/ChroZn (zinc chromate) or EP/Charge was investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy measurements were utilized. It was found that the addition of three forms of PAni—undoped, sulfonated and fibers—to the EP resin increased its corrosion protection efficiency.     

Localized EIS characterization of corrosion of steel at coating defect under cathodic protection

Localized electrochemical impedance spectroscopy (LEIS) technique was used to investigate localized corrosion of steel at defect of coating and, furthermore, to determine the effects of cathodic protection (CP) on local electrochemical environment and the resultant corrosion reaction at the base of coating defect. The results demonstrated that corrosion of steel is dependent on CP potential and the defect geometry. For coated steel containing defect under appropriate CP potentials, cathodic reaction is dominated by reduction of oxygen. Mass-transfer of oxygen through solution layer and the defect with a narrow, deep geometry (the depth/width ratio is about 5.5) is the rate-limiting step for the corrosion process of steel. Even at a very negative potential, e.g., −1200 mV (SCE), the measured impedance spectroscopy is still associated with the diffusion-controlled charge-transfer reaction of steel at the base of defect. It is attributed to the fact that the applied CP is partially shielded by the defect with a narrow, deep geometry. With the negative increase of cathodic potential, charge-transfer resistance and the local impedance of electrode increase. It is attributed to the elevation of local alkalinity at the base of defect when the coated steel is under CP. This conclusion is subject to the condition that a significant cathodic disbonding of coating has not occurred. Furthermore, with the increase of test time, the charge-transfer resistance increases, which is attributed to the enhancement of the alkaline environment at the base of defect under CP with time.     

Electrochemical and spectroscopic evidences of corrosion inhibition of bronze by a triazole derivative

The electrochemical behavior of the bronze (Cu-8Sn in wt%) was investigated in 3% NaCl aqueous solution, in presence and in absence of a corrosion inhibitor, the 3-phenyl-1,2,4-triazole-5-thione (PTS). The inhibiting effect of the PTS was evidenced for concentrations higher than 1 mM for the cathodic process whereas its effect was clearly seen with a concentration as low as 0.1 mM for the anodic process. A significant positive shift of the corrosion potential was also observed, and its inhibiting effect increased with both its concentration and the immersion time of the sample. From voltammetry and electrochemical impedance spectroscopy experiments, the inhibiting efficiency of the PTS was found to be in the 94-99% range for 1 mM concentration. Scanning electron microscopy and X-ray energy dispersion analysis of the specimen surface show the presence of sulphur on the surface. Raman micro-spectrometry study confirms the protective effect of the PTS in aqueous solution through three types of interactions with the electrode, namely the adsorption of the inhibitor in a flat configuration, the formation of copper-thiol molecules, and when copper is released, the formation of a polymeric complex.     

Electrochemical behavior of (Cr,W, Al,Ti, Si)N multilayer coating on nitrided AISI 316L steel in natural seawater

AISI 316L steel is often used in materials applied toward nuclear power but are subjected to pitting corrosion in a marine environment. In this study, (Cr, W, Al, Ti, Si)N multilayer coatings were deposited using multi-arc ion plating on the surface of non-nitrided and nitrided AISI 316L steel. The microstructure and corrosion resistance of four different systems were investigated, namely, (i) untreated AISI 316L steel, (ii) plasma nitrided (PN), (iii) coated on an untreated matrix (coating) only, and (iv) coated on nitrided (hybrid) specimens. The phase structures, morphologies, and compositions of the different specimens were characterized using X-ray diffraction, transmission electron microscope, Atomic Force Microscope, scanning electron microscope, X-ray photoelectron spectroscopy, and energy dispersive x-ray spectroscopy. The results show that a thin CrWAlTiSiN multilayer coating, approximately 2.3 μm in thickness, is deposited on the surface of an ~12 μm nitrided layer. Potentio-dynamic polarization and electrochemical impedance spectroscopy were used to evaluate the assessment of the electrochemical behavior in the natural seawater of China's Yellow Sea. The hybrid specimens exhibited excellent corrosion resistance compared to both the nitrided and coated specimens.     

Electrochemical frequency modulation as a new technique for monitoring corrosion inhibition of iron in acid media by new thiourea derivative

The electrochemical frequency modulation EFM technique provides a new tool for electrochemical corrosion monitoring. EFM is a non-destructive technique as electrochemical impedance spectroscopy (EIS). EFM technique was used in comparison with the traditional dc and ac techniques. Results obtained by EFM technique were shown to be in agreement with other electrochemical techniques. With EFM technique, a corrosion rate can be obtained instantaneously in very short time which makes this technique ideal in online corrosion monitoring. New synthesized thiourea derivative named 1,3-diarylidenethiourea (DAT) was examined as a new corrosion inhibitor for iron in 1 M hydrochloric acid solution.     

Corrosion protection of magnesium alloy ZM21 by polyaniline-blended coatings

Phosphate-doped polyaniline pigment was prepared by a chemical oxidation method using ammonium persulfate in phosphoric acid media. Fourier transform infrared studies were done to characterize the pigment. The magnesium alloy ZM 21 was coated with polyaniline-pigmented paint, based on an epoxy binder, and the corrosion performance of the coating was studied by potential measurements and electrochemical impedance spectroscopy in 0.1% and 0.5% NaCl solutions. The results were compared with strontium chromate and filler material-pigmented coatings. It was found that the coating containing polyaniline provided similar protection for the magnesium alloy as that offered by chromate-pigmented paint.     

EIS investigation of passive film formation on mild steel in oxalic acid solution

The properties of oxide films on mild steel formed anodically in aqueous solution containing oxalic acid were investigated by means of electrochemical impedance spectroscopy (EIS). The morphology of the passive layers at different stages of film formation was investigated using scanning electron microscopy (SEM). Passivation of mild steel in oxalic acid solution is a multi-stage process that occurs before passive layer breakdown. The influence of potential on the electrochemical behavior of the passive layer was also investigated. Depending on the passive layer potential, the EIS spectra obtained exhibited a one- or two-time constant system. This suggests the formation of either a one layer or two layer oxide film on the mild steel surface, depending on the passivation potential.     

Inhibitive effect of FA derivatives on mild steel corrosion in the presence of formic acid

The influence of selected long-chain FA hydrazides and thiosemicarbazides on the corrosion inhibition of mild steel in the presence of 20% formic acid was studied. The inhibition efficiency of these compounds varied with concentration, temperature, and immersion time. All the FA derivatives in the formic acid solution followed Temkin's adsorption isotherm. The activation energies and free energies of adsorption of all the hydrazides and thiosemicarbazides also were calculated. Potentiodynamic polarization studies indicated that all the tested compounds were of mixed type. Electrochemical impedance spectroscopy was also used to investigate the mechanism of corrosion inhibition.     

A comparative study of epoxy and polyurethane based coatings containing polyaniline-DBSA pigments for corrosion protection on mild steel

Organic coatings based on epoxy and polyurethane matrices containing polyaniline doped with dodecyl benzene sulfonic acid (Pani-DBSA) were prepared and applied over steel plates (SAE 1020). The plates were submitted to salt spray chamber for up to 30 days in order to evaluate the corrosion protection of these coatings. The properties of the coated plates were analyzed as a function of time by electrochemical impedance spectroscopy, open circuit potential, optical microscopy, and Raman spectroscopy. In general, results indicate a decrease in the electrical resistance, increase in capacitance and decrease in open circuit potential. Epoxy based coatings have improved performance when Pani-DBSA is used as pigment, whereas for the polyurethane coatings, Pani-DBSA seems to play an adverse effect. Raman spectroscopy indicates a possible chlorination of the epoxy matrix after 30 days exposure to salt spray chamber.     

Effect of sodium molybdate on the corrosion behavior of cold rolled steel in peracetic acid solution

The effect of sodium molybdate (Na₂MoO₄) on the corrosion of cold rolled steel (CRS) in peracetic acid (PAA) solution was investigated by gravimetric measurements, Tafel polarization curves, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). All the data indicate that Na₂MoO₄ acts as a very good inhibitor in PAA solution. The inhibition efficiency increases with increasing concentration of Na₂MoO₄ and immersion time. The inhibition efficiencies, calculated from gravimetric measurements, Tafel polarization curves and electrochemical impedance spectroscopy, are in reasonably good agreement and are very similar in the three cases. Furthermore, polarization data show that Na₂MoO₄ behaves as an anodic passive type inhibitor. Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used to characterize the corrosion surface. A probable mechanism is presented to explain the experimental results.     

Hector bases – a new class of heterocyclic corrosion inhibitors for mild steel in acid solutions

Three heterocyclic compounds namely 3-anilino-5-imino-4-phenyl-1, 2,4-thiadiazoline (AIPT), 3-anilino-5-imino-4-tolyl-1, 2,4-thiadiazoline (AITT), and 3-anilino-5-imino-4-chlorophenyl-1, 2,4-thiadiazoline (AICT) were synthesized and their influence on the inhibition of corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ was investigated by weight loss and potentiodynamic polarization techniques. The values of activation energy and free energy of adsorption of these compounds were also calculated. Potentiodynamic polarization studies were carried out at room temperature, and showed that all the compounds were mixed type inhibitors causing blocking of active sites on the metal. The inhibition efficiency of the compounds was found to vary with concentration, temperature and immersion time. Good inhibition efficiency was evidenced in both acid solutions. The adsorption of the compounds on mild steel for both acids was found to obey the Langmuir adsorption isotherm. Electrochemical impedance spectroscopy was also used to investigate the mechanism of corrosion inhibition.     

Electrochemical impedance studies of corrosion protected surfaces covered by epoxy polyamide coating systems

Electrochemical impedance spectroscopy (EIS) was used to study the corrosion behavior of different types of commercial quality epoxy polyamide dry coatings on mild steel, with thickness between 150 and 250 μm, which were previously weather accelerated in a wet chamber. The following data were established on the basis of impedance curves and corresponding equivalent circuits: the coating capacity that relates to the coating dimension, the pore resistance that represents conductive paths through the pores, and Warburg coefficients, which are the measure of ion diffusion through the coating. EIS data were compared with a criterion in the European standard, and samples were classified on the basis of their quality, also receiving a final ranking by summing-up all the individual rankings. Suggestions have been made, namely that the use of anticorrosive active pigments is obsolete, when the thickness of the coatings exceeds 200 μm.     

Eco friendly inhibitor for corrosion inhibition of mild steel in phosphoric acid medium

The inhibition effect of Zenthoxylum alatum plant extract on the corrosion of mild steel in 20, 50 and 88% aqueous orthophosphoric acid has been investigated by weight loss and electrochemical impedance spectroscopy (EIS). Plant extract is able to reduce the corrosion of steel more effectively in 88% phosphoric acid than in 20% phosphoric acid. The effect of temperature on the corrosion behaviour of mild steel in 20, 50 and 88% phosphoric acid with addition of plant extract was studied in the temperature range 50-80 °C. Results on corrosion rate and inhibition efficiency have indicated that this extract is effective up to 70 °C in 88% phosphoric acid medium. Surface analysis (XPS and FT-IR) was also carried out to establish the mechanism of corrosion inhibition of mild steel in phosphoric acid medium.     

Electrochemical impedance spectroscopic investigation of the role of alkaline pre-treatment in corrosion resistance of a silane coating on magnesium alloy, ZE41

The protective performance of the coatings of bis-1,2-(triethoxysilyl) ethane (BTSE) on ZE41 magnesium alloy with different surface pre-treatments were evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.1 M sodium chloride solution. Electrical equivalent circuits were developed based upon hypothetical corrosion mechanisms and simulated to correspond to the experimental data. The morphology and cross section of the alloy subjected to different pre-treatments and coatings were characterized using scanning electron microscope. A specific alkaline pre-treatment of the substrate prior to the coating has been found to improve the corrosion resistance of the alloy.     

Corrosion of steel under the defected coating studied by localized electrochemical impedance spectroscopy

Corrosion of steel under the defected coating in near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS) measurements. The LEIS response is dependent on the size of the defect. For small defects, e.g., less than 200 μm in diameter, localized corrosion process and mechanism of steel, as indicated by the measured LEIS plots, change with time. The diffusion process dominates the interfacial corrosion reaction, which is due to the block effect of the deposited corrosion product combined with the geometrical factor of a large coating thickness/defect width ratio. In the presence of a big defect, e.g., up to 1000 μm, the LEIS responses measured at the defect are always featured by a coating impedance in the high-frequency range and an interfacial corrosion reaction in the low-frequency range. The block effect of corrosion product does not apply due to the relatively open geometry. Conventional EIS measurements on a macroscopic-coated electrode reflect the “averaged” impedance results from both coating and defect. The information of the localized electrochemical corrosion processes and mechanisms at the small defect is lost, and the coating impedance information is “averaged” out when a big defect is contained. LEIS measurement provides an essential technique to characterize microscopically the local electrochemical corrosion reaction of steel under the defected coating.     

Corrosion inhibition by fatty acid triazoles for mild steel in formic acid

5-Heptadec-8-enyl-4-phenyl-4H–[1,2,4] triazole-3-thiol (HPTT), 4-phenyl-5-undecyl-4H–[1,2,4] triazole-3-thiol (PUTT), and 5-dec-9-enyl-4-phenyl-4H–[1,2,4] triazole-3-thiol (DPTT) were synthesized and their influence on the inhibition of corrosion of mild steel in 20% formic acid was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency of these compounds was found to vary with their nature and concentration, temperature and immersion time. The values of activation energy and free energy of adsorption of the triazoles were calculated to investigate the mechanism of corrosion inhibition. Good inhibition efficiency (>90%) was found even at lower concentration (i.e., 25 ppm) in acid solution. The adsorption on mild steel surfaces was found to obey Temkin's adsorption isotherm. Potentiodynamic polarization results revealed that the compounds studied are mixed type inhibitors. Electrochemical impedance spectroscopy was also used to investigate the mechanism of the corrosion inhibition.     

Comparisons of clear coating degradation in NaCl solution and pure water

Organic coating's degradation behavior is essential to its corrosion protective function and has been widely studied. A main function of anti-corrosive organic coatings is acting as barriers to water uptake and ion diffusion. It is of great fundamental importance to study the influence of different working fluids on the degradation of organic coatings. In this study, a 3.5 wt% NaCl solution and the pure water are adopted as the working fluids based on their distinct properties. The commercially available polyurethane and epoxy based clear coatings are chosen for evaluation. The coating degradation is monitored by electrochemical impedance spectroscopy (EIS) measurement. Equivalent circuit models are employed to interpret the EIS spectra. The time evolution of coating resistance, capacitance, and water volume fraction of the coating is analyzed. Besides the fact that the coating's barrier property is deteriorated by the percolating of both NaCl solution and pure water, we also discover that pure water leads to faster coating degradation, demonstrated by a more substantial decrease in coating resistance, a more prominent increase in coating capacitance, and a greater saturated water volume fraction.