The improvement of anticorrosion properties of zinc-rich organic coating by incorporating surface-modified zinc particle

The corrosion behaviors of zinc-rich coating with various zinc contents, ranging from 0 to 60 volume percent, in thin organic coatings (below 5 μm) were characterized by electrochemical impedance spectroscopy (EIS), free corrosion potential (E_corr) measurement and cycle corrosion test (CCT). It was verified that both coatings with 60 volume percent of zinc powder and without zinc powder showed good corrosion resistance mainly due to the cathodic protection and barrier effect, respectively. On the other hand, coatings with an intermediate concentration (10–40 vol.%) of zinc powder was not successful in protecting a steel substrate efficiently. To improve anticorrosion property of zinc-rich coating, the surface modification of zinc particle was carried out with derivatives of phosphoric and phosphonic acid in the aqueous solution. The effects of the surface modification of zinc particle on corrosion resistance of the coating were investigated with scanning vibrating electrode technique (SVET) and X-ray photoelectron spectroscopy (XPS). The best anti-corrosion performance was achieved when the incorporated zinc particle was treated with phosphoric acid 2-ethylhexyl ester and calcium ion simultaneously, which induced the formation of alkyl-phosphate-calcium complex layer of 190 nm in thickness on zinc particles. Corrosion resistance was improved by the decreased zinc activity and the increased compatibility between the formed complex layer on zinc surface and polymer binder matrix.     

Mica/polypyrrole (doped) composite containing coatings for the corrosion protection of cold rolled steel

Micas/polypyrroles (PPys) doped with molybdate, p-toluene sulfonate, dodecyl benzene sulfonate, and 2-naphthalene sulfonate composite pigments were synthesized by chemical oxidative polymerization and characterized in coatings for corrosion protection on cold rolled steel substrate by various electrochemical techniques. Synthesized composite pigments were characterized for morphology by scanning electron microscopy, which indicated physical formation of PPy on the surface of mica. Chemical composition of the composite pigments was analyzed by X-ray photoelectron spectroscopy which chemically confirmed doped PPy formation on the mica surface. Coatings were formulated at 20% pigment volume concentration (composite pigments or as-received mica pigment) and were applied on cold rolled steel substrate. Coatings were exposed to salt spray test conditions (ASTM B117) for 30 days and were periodically assessed for corrosion with electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and potentiodynamic polarization. EIS and circuit modeling results demonstrated higher coating resistance (R _c) for mica/PPy (doped) composite coatings as compared to as-received mica pigment containing coating after 30 days of salt spray exposure. Lower current density and more positive corrosion potential values were observed for mica/PPy (doped) composite coatings as compared to mica pigment-based coating in potentiodynamic polarization measurements, indicating improved corrosion protection for cold rolled steel substrate. OCP measurements revealed more positive values for mica/PPy (doped) composite coatings as compared to mica pigment-based coating suggesting superior corrosion protection for mica/PPy (doped) composites.     

Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte

The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn²⁺ and Al³⁺ ions. The low pH value was further confirmed by observing evolution of gas due to H⁺ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test.     

Epoxy/polyaniline–ZnO nanorods hybrid nanocomposite coatings: Synthesis,characterization and corrosion protection performance of conducting paints

The objective of this research is the production of an epoxy coating blended with organic–inorganic hybrid nanocomposite as a corrosion inhibiting pigment applied over carbon steel grade ST37. A series of conducting polyaniline (PANI)–ZnO nanocomposites materials has been successfully prepared by an in situ chemical oxidative method of aniline monomers in the presence of ZnO nanorods with camphorsulfonic acid (CSA) and ammonium peroxydisulfate (APS) as surfactant and initiator, respectively. The synthesized polymers were characterized by X-ray diffraction pattern (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and electrical conductivity techniques. Synthesized nanocomposites were solved in tetraethylenpentamine (TEPA), and then prepared solution was mixed with epoxy and then was applied as a protective coating on carbon steel plates. The anti-corrosion behavior of the epoxy binder blended with PANI–ZnO nanocomposites were studied in 3.5% NaCl solution at a temperature of 25 °C by electrochemical techniques including electrochemical impedance spectroscopy (EIS) and chronopotentiometry at open circuit potential (OCP). It was observed that the epoxy coating containing conducting PANI–ZnO nanocomposites exhibited higher corrosion resistance and provided better barrier properties in the paint film in comparison with pure epoxy and epoxy/PANI coatings. In the case of conducting coatings, the OCP was shifted to the noble region due to presence of PANI pigments. Additionally, the possibility of formation of a passive film in the presence of PANI was reinforced at the substrate–coating interface. SEM studies taken from surface of the coatings showed that epoxy/PANI–ZnO hybrid nanocomposite coating systems (EPZ) are crack free, uniform and compact. Furthermore, it was found that the presence of ZnO nanorods beside PANI can significantly improve the barrier and corrosion protection performance of the epoxy coating due to the flaky shaped structure of the PANI–ZnO nanocomposites.     

Corrosion behaviour of electrogalvanized steel in sodium chloride and ammonium sulphate solutions; a study by E.I.S.

Zinc and zinc-nickel (13% Ni) electrodeposits were passivated by dipping in chromate baths and characterized by scanning electron microscopy. The corrosion behaviour was studied using a.c. electrochemical techniques; electrochemical impedance spectroscopy (EIS) measurements were performed at open circuit and under galvanostatic control during the 24 h immersion time. In sodium chloride solution the zinc-nickel electrodeposits show a better corrosion resistance compared to the pure zinc coatings. During the immersion time, a surface nickel enrichment was observed which, together with the zinc corrosion products, acts as a barrier layer reducing the total corrosion rate. In the same solution the passivation treatment improves the corrosion resistance of the electrodeposits; nevertheless, on zinc substrates, the protection exerted by the chromate film is not, always effective during the immersion time. On the contrary the chromate coating on zinc-nickel substrates induces a remarkable and durable improvement of the corrosion resistance reducing the zinc dissolution almost completely. In the ammonium sulphate solution, the corrosion mechanism is significantly influenced by hydrogen reduction on the zinc-nickel surfaces, and by the production of a local surface acidity which is aggressive for the chromate coatings.     

High corrosion protection of a polyaniline/organophilic montmorillonite coating for magnesium alloys

Epoxy coatings containing polyaniline (PANI) and polyaniline/organophilic montmorillonite (PANI/OMMT) powders were prepared on the surface of AZ91D magnesium alloy. The corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and open-circuit potential analysis in 3.5% NaCl. The results indicate that the PANI/OMMT coating retained its high corrosion protection for AZ91D magnesium alloy after 6000 h of immersion. The protective mechanism conferred by the PANI/OMMT coating was also discussed. The effects of oxygen on the protective mechanism of PANI were evaluated by EIS measurements in a 3.5% deaerated NaCl solution.     

Inhibition of nickel coated mild steel corrosion by electrosynthesized polyaniline coatings

Polyaniline (PANI) coatings were electrochemically synthesized on nickel (Ni) coated mild steel (MS) and their corrosion protection properties were investigated. In this work, the Ni layer (∼1 μm thick) was electrodeposited on MS under galvanostatic condition. Thereafter, the PANI coating was deposited over the Ni layer from aqueous salicylate medium by using cyclic voltammetry. These bi-layered composite coatings were characterized by cyclic voltammetry, UV–vis absorption spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The corrosion protection properties of Ni coated MS (Ni/MS) and PANI coated Ni/MS (PANI/Ni/MS) were investigated in aqueous 3% NaCl by using open circuit potential (OCP) measurements, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). It was shown that the top layer of PANI exhibits a lower porosity behavior with respect to Ni coating and reduces the corrosion rate of Ni/MS almost by a factor of 3500 and increases the lifetime of Ni coating.     

Eco‐friendly,acrylic resin‐modified potassium silicate as water‐based vehicle for anticorrosive zinc‐rich primers

Potassium silicate binder of zinc‐rich coating was modified by adding water‐based acrylic resin. Several series of coatings containing 5, 10, and 15 wt % of acrylic and acrylic/styrene binders were added to potassium silicate. The coatings were applied on steel and the corrosion resistance of coatings was evaluated by conventional methods such as electrochemical impedance spectroscopy, corrosion potential, salt spray, and scanning electron microscopy. The results indicated that the modification of silicate binder with acrylic and acrylic/styrene led to shortening the curing time, improved corrosion protection, better dispersion of zinc particles, and enhanced salt spray resistance of resultant coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40370.     

Conducting polymer based hybrid nano-composites for enhanced corrosion protective coatings

Hybrid composite coatings containing zinc oxide (ZnO) and polyaniline (PANI) as nano-additives dispersions were prepared with poly(vinyl acetate) (PVAc) as the major matrix. The steel plates dip-coated with these formulations were tested for corrosion protection by immersion in saline water over long periods. The Tafel plots for the determination of open circuit potential (OCP) and corrosion current (I_corr) were recorded. The coatings containing both ZnO and PANI showed improved corrosion resistance as compared to the single component coating. The I_corr values of PVAc–ZnO–PANI are found to be two-order magnitude lower than that of PVAc and PVAc–ZnO coatings. The results are explained on the basis of enhancement in barrier properties due to nano-particulate additives in PVAc–ZnO–PANI film together with the redox behaviour of PANI and protective oxide layer formation near the substrate.     

Inhibition of steel corrosion by electrosynthesized poly(o-anisidine)-dodecylbenzenesulfonate coatings

Poly(o-anisidine)-dodecylbenzenesulfonate (POA-DBSA) coatings were synthesized on stainless steel from aqueous solution containing o-anisidine and dodecylbenzene sulfonic acid by using cyclic voltammetry. These coatings were characterized by Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Corrosion tests of these coatings were carried out in aqueous 3% NaCl solution by using open circuit potential (OCP) measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The results reveal that POA-DBSA acts as a corrosion protective coating on steel and reduces the corrosion rate (CR) of steel almost by a factor of 14.5.     

Zinc deposited polymer coatings for copper protection

Polypyrrole (PPy) and polyaniline (PAni) coatings were electrosynthesized on copper, by using cyclic voltammetry technique. Then, these coatings were modified with the deposition of zinc particles from aqueous zinc sulphate solution. The electrodeposition of zinc was achieved at a constant potential value of −1.20 V, in the amount of ∼0.75 mg/cm². The corrosion performance of zinc modified polymer coatings were investigated in 3.5% NaCl solution; by using the electrochemical impedance spectroscopy (EIS), and anodic polarization curves. The zinc particles improved the barrier property of polymer films, thanks to formation of voluminous zinc corrosion products within the pores of polymer coating. Also, the zinc particles provided cathodic protection to the substrate, where the polymer film played the role of conductance between zinc particles and copper.     

Corrosion protection assessment of sacrificial coating systems as a function of exposure time in a marine environment

The present investigation assessed the corrosion protection performance of 17 different Zn and Al sacrificial coating system configurations during marine atmospheric exposure at Kure Beach, NC. The coating systems incorporated several conversion coating layers, primers and organic topcoats. Visual observations and electrochemical measurements (including electrochemical impedance spectroscopy, EIS) were made on six different occasions throughout the 20-month exposure time. Milled scribes on each of the coating specimens allowed for defect protection as well as barrier protection to be investigated. A novel corrosion analysis technique utilizing a specialized conducting agar (SCAR) cell enabled impedance measurements to be made on both intact and defect areas. Visual observations, E_oc's, and EIS as a function of atmospheric exposure time provided complementary results. Impedance results were found to be useful in determining a coating's barrier protection and scribe damage analysis accurately represented defect protection.     

Electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings

In this work, hydrochloride polyaniline (PANI-Cl) powder was incorporated as a conductive pigment into powder zinc-rich primer (ZRP) formulations in order to enhance the electronic conduction paths between zinc particles inside the coating and the steel substrate (i.e. percolation). Coatings were applied onto steel substrates and immersed in a 3% NaCl solution at ambient temperature.The protective properties and electrochemical behaviour of coatings were investigated by monitoring the free corrosion potential versus time and by using EIS. It was found that corrosion potential remains cathodic and constant for a long time up to 100 days of immersion. From EIS results, it was shown that the coatings exhibit larger impedance values than those observed with liquid or other zinc-rich powder formulations containing carbon black. From Raman spectroscopy results, it may be proposed that zinc particles in contact with PANI-Cl pigments were passivated. Other zinc particles remain still active which ensures the cathodic protection of the substrate. Moreover, coatings exhibit good barrier properties.     

In-situ AFM and EIS study of a solventborne alkyd coating with nanoclay for corrosion protection of carbon steel

A solventborne alkyd composite coating containing modified montmorillonite (MMT) nanoclay was made on carbon steel, and its corrosion protection was investigated by in-situ atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) measurements in 3 wt.% NaCl solution. X-ray diffraction (XRD) analysis indicated intercalation of the MMT sheets in the composite coating. Thermo-gravimetric analysis (TGA) demonstrated improved thermal stability of the composite coating due to the modified nanoclay. Scanning electron microscopy (SEM) and AFM examination revealed dispersion and also some aggregation of the nanoclay particles in the coating. In-situ AFM images show a stable coating surface at nano-scale during relative long time exposure in the NaCl solution, indicating an enhanced stability of the composite coating. The EIS results confirmed that the composite coating provides an enhanced barrier type corrosion protection for carbon steel in the corrosive solution, which could be attributed to the intercalated lamellar MMT sheets in the coating that block the defects and decrease the transport of water and corrosive species.     

Corrosion protection with zinc-rich epoxy paint coatings embedded with various amounts of highly dispersed polypyrrole-deposited alumina monohydrate particles

Active anodic zinc content below 90 wt.% does not support sufficient electrical contacts but higher contents cause high porosity of traditional liquid zinc-rich paints (ZRPs). To resolve this problem, our proposal is the application of highly dispersed polypyrrole (PPy) coated alumina inhibitor particles (PCAIPs) in zinc-rich paint compositions. Using these nano-size inhibitor particles at concentrations from 4.55 to 0.85 wt.%, hybrid paints were formulated with zinc contents ranging from 60 to 85 wt.% at the same time. Submicron morphology and nano-scale structure, spectroscopy characteristics and electrochemical properties of the PCAIPs were studied by transmission electron microscopy (TEM) and rheology, Fourier-transform infrared spectroscopy (FT-IR) and cyclic voltammetry (CV) in first part of the work. In the second part, electrolytic corrosion resistivity of two sets of paint coatings were salt-spray chamber and immersion tested with 5 wt.% aqueous solution of sodium chloride. Active corrosion prevention ability of the salt-spray tested coatings was evaluated in compliance with ISO recommendations. Dielectric properties of the coatings during the immersion tests were monitored by electrochemical impedance spectroscopy (EIS). Corrosion tested area of the coatings was investigated by glow-discharge optical emission spectroscopy (GD-OES) to disclose infiltration of corrosive analytes and oxygen enrichment in the cross-section of the primers in comparison with their pristine states. Morphology of the zinc pigments was examined by scanning electron microscopy (SEM), and quality of steel specimens and the interfacial binder residues by X-ray photoelectron spectroscopy (XPS) as well as FT-Raman and Mössbauer spectroscopy. The results of both types of corrosion tests evidenced efficient utilisation of sacrificial anodic current for galvanic protection and improved barrier profile of the hybrid coatings, along with the PCAIP inhibited moderate self-corrosion of zinc. As a result of well balanced active/passive function, the hybrid coating containing zinc at 80 wt.% and PCAIPs at 1.75 wt.% embedding PPy at 0.056 wt.% indicated the most advanced corrosion prevention. Galvanic function of the hybrid paints is interpreted on the basis of size-range effect and spatial distribution of the alumina supported PPy inhibitor particles and basic electrical percolation model considerations.     

新型活化环氧富锌涂层的耐腐蚀性研究

富锌涂料在防腐蚀领域具有广泛应用,然而其长效防护性能却受到锌粉活性影响。本文以冷涂锌涂层、传统环氧富锌涂层作为对照,研究了新型具有电化学活性的环氧富锌涂层在盐雾加速腐蚀试验后的耐腐蚀性。宏观形貌分析表明:盐雾加速腐蚀1 800 h后,活化环氧富锌涂层表面并未出现锈点;采用扫描电子显微镜、维体式显微镜观察试验后涂层的表面形貌和涂层结构,发现活化环氧富锌涂层微观表面更加平滑,锌粉并未出现大面积的氧化,涂层内部大小锌粉颗粒均匀排列;通过电化学方法研究涂层的耐蚀机理与防护性,发现活化富锌涂层具有更持久的低防护电位。以上研究结果表明,较冷涂锌及传统环氧富锌涂层而言,新型活化环氧富锌涂层具有优异的长期防护性能,是值得关注和研究的一种新型技术。     

Conducting polymer based hybrid nano-composites for enhanced corrosion protective coatings

Hybrid composite coatings containing zinc oxide (ZnO) and polyaniline (PANI) as nano-additives dispersions were prepared with poly(vinyl acetate) (PVAc) as the major matrix. The steel plates dip-coated with these formulations were tested for corrosion protection by immersion in saline water over long periods. The Tafel plots for the determination of open circuit potential (OCP) and corrosion current (I_corr) were recorded. The coatings containing both ZnO and PANI showed improved corrosion resistance as compared to the single component coating. The I_corr values of PVAc–ZnO–PANI are found to be two-order magnitude lower than that of PVAc and PVAc–ZnO coatings. The results are explained on the basis of enhancement in barrier properties due to nano-particulate additives in PVAc–ZnO–PANI film together with the redox behaviour of PANI and protective oxide layer formation near the substrate.     

Enhanced corrosion protective coating based on conducting polyaniline/zinc nanocomposite

Conducting polyaniline (PANI) is being explored as promising material for protection of metals against corrosion. It has the possibility of making smart coatings on metals, which can prevent corrosion even in scratched areas where bare metal surface is exposed to the aggressive environment. However, PANI coatings have poor barrier and mechanical properties. The barrier property of coatings can be enhanced by the addition of appropriate filler particles. Also it has been demonstrated that nanoparticulate fillers give much better barrier properties even at lower concentrations. In this study, the effect of zinc nanoparticles on the anticorrosive property of PANI coating on iron samples has been investigated. The PANI/Zn nanocomposite was synthesized by in situ polymerization of aniline in the presence of Zn nanoparticles. The nanocomposite was characterized by using FTIR, conductivity measurement, cyclic voltammetry, and AFM techniques. Results showed that PANI/Zn nanocomposite coating has improved corrosion protection effect when compared with pure PANI coating. The corrosion current of PANI/Zn coated samples were found to be much lower than that of pure PANI coated samples. The results were referred to the good barrier properties of Zn nanoparticles and improvement in electrochemical corrosion protection of PANI coating in the presence of Zn nanoparticles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Corrosion resistant performance of hydrophobic poly(N-vinyl imidazole-co-ethyl methacrylate) coating on mild steel

Functional copolymers are often used as protective coating against corrosion. In this research article, we have applied poly(NVI-co-EMA) coating over the mild steel surface which provides barrier protection against corrosion in aggressive environment. Hydrophobic nature of the copolymer film may augment the corrosion resistance behavior and thermal stability of the copolymer also influences the corrosion protection. Thus, the coating precluded the corrosive elements and corrosion products from diffusing through the coating. EIS technique revealed that the mild steel coated with hydrophobic copolymer film, which is immersed in 3% NaCl solution provides excellent protection from corrosion. Further, it is evidenced by protection efficiency of the copolymer which is greater than 90%. The results from surface analysis techniques like SEM, AFM and FTIR also supports and confirms a very thin film on the metal surface with excellent anticorrosion effects.     

Electrochemical behavior and anticorrosion properties of modified polyaniline dispersed in polyvinylacetate coating on carbon steel

Conducting polyaniline (Pani) was prepared in the presence of methane sulfonic acid (MeSA) as dopant by chemical oxidative polymerization. The Pani-MeSA polymer was characterized by FT-IR, UV-vis, X-ray diffraction (XRD) and impedance spectroscopy. The polymer was dispersed in polyvinylacetate and coated on carbon steel samples by a dipping method. The electrochemical behavior and anticorrosion properties of the coating on carbon steel in 3% NaCl were investigated using open-circuit potential (OCP) versus time of exposure, and electrochemical techniques including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic voltammetry (CV). During initial exposure, the OCP dropped about 0.35 V and the interfacial resistance increased several times, indicating a certain reduction of the polymer and oxidation of the steel surface. Later the OCP shifted to the noble direction and remained at a stable value during the exposure up to 60 days. The EIS monitoring also revealed the initial change and later stabilization of the coating. The stable high OCP and low coating impedance suggest that the conducting polymer maintains its oxidative state and provides corrosion protection for carbon steel throughout the investigated period. The polarization curves and CV show that the conducting polymer coating induces a passive-like behavior and greatly reduces the corrosion of carbon steel.