Formulation and performance evaluation of hydroxyl terminated hyperbranched polyesters based poly (ester–urethane–urea) coatings on mild steel

A low molecular weight, anticorrosive hyperbranched poly (ester–urethane–urea) [HB-P(EUU)] coatings were formulated using 2nd generation hydroxyl terminated hyperbranched polyesters (OH–HBPEs), isophorone di-isocyanate (IPDI) as a cross linking agent and dibutyltin dilaurate (DBTDL) as a catalyst with certain additives. First, NCO terminated prepolymers (HBPEUs) were formulated by reacting OH–HBPEs with IPDI at NCO:OH ratio of 1.1:1 for 4 h at 70–80 °C, then HBPEUs were mixed with DBTDL and various additives and finally coated on pretreated cold rolled mild steel (MS) substrates by dip coating method. Before applying on MS substrates, viscosity and volume solid of coatings were measured. The molecular structure of HBPEUs was characterized by ATR-FTIR and ¹H NMR analysis. Surface morphology of coated panels was characterized by atomic force microscopy (AFM) and found that coating components were homogeneously distributed and surface was smooth and crack free. Performance of coated substrates was evaluated by various tests such as cross hatch and pull off adhesion, abrasion resistance, scratch resistance, impact resistance, flexibility, and pencil hardness. UV stability of coated substrates was evaluated by UV-whether-o-meter and corrosion resistance property was evaluated by salt spray, humidity, polarization and electrochemical impedance (EIS) test. Results were also compared with polyurethane coating based on linear polyester. HB-P(EUU) coatings showed excellent enhancement in mechanical, durability as well as corrosion resistance properties than their linear counterpart.     

High performance corrosion protective DGEBA/polypyrrole composite coatings

Conducting polymers (CP) have been envisaged as nontoxic substitutes for chromates in corrosion protective coatings owing to their environmental stability, excellent corrosion resistant performances and good adhesion to metal substrate. Recent advancements in the field of corrosion protective coatings have therefore headed towards the utilization of conducting polymers as “smart corrosion inhibitors” in the formulation of eco-friendly anti-corrosive coatings. With the aim to develop a facile method for the synthesis of anti corrosive coating material having superior corrosion protective properties, the present work reports the corrosion studies of polypyrrole/DGEBA composite coatings on mild steel (MS). The coatings were characterized by physicochemical as well as physicomechanical studies while the corrosion protective performance was evaluated by chemical resistance in different corrosive media, corrosion rate and open circuit potential (OCP) measurements. The morphologies of corroded, coated, uncorroded and uncoated samples were investigated by SEM studies. The composite coatings were found to show far superior anti corrosive performance than PANI/epoxy coatings in acid, alkaline as well as saline environments.     

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 of mild steel with composite polyaniline coatings using different formulations

The protective abilities of composite coatings based on electrochemically and chemically formed polyaniline powder against the corrosion of mild steel were investigated. A polyaniline powder has been prepared in the form of an emeraldine base and benzoate salt through chemical dedoping and doping. The composite coatings using polyaniline powders, which were obtained through different routes, and base coatings, which were not corrosion-resistant, with different formulations were prepared and applied on mild steel samples. The corrosion was investigated using an electrochemical impedance technique in 3% NaCl, and the atmospheric corrosion was assessed in a humidity chamber. Emeraldine–benzoate salts, which are a chemically synthesized polyaniline, offer the best protection with an optimal polyaniline concentration of approximately 5 wt%. The different corrosion behaviors were assessed relative to the presence of aniline oligomers in the samples after characterization using UV–vis spectrophotometry. Upon comparison between the corrosion behavior in 3% NaCl with commercial primer paint for iron and that with a paint containing 5 wt% PANI, the composite coating has superior anticorrosion characteristics. The mechanism for the protection of mild steel from corrosion through composite polyaniline coatings was also considered.     

Styrene butadiene co-polymer based conducting polymer composite as an effective corrosion protective coating

Electroactive conducting polymer composite coatings of polyaniline (PANI) are electrosynthesized on styrene–butadiene rubber (SBR) coated stainless steel electrode by potentiostatic method using aqueous H₂SO₄ as supporting electrolyte. The protective behaviour of these coatings in different corrosion media (3.5% NaCl and 0.5 M HCl) is investigated using Tafel polarization curves, open circuit potential measurements and electrochemical impedance spectroscopy. The results reveal that SBR/PANI composite coating is much better in corrosion protection than simple PANI coating. The corrosion potential of composite films shifts to more noble values indicating that SBR/PANI composite coating act as an effective corrosion protective layer.     

Aktuelle Fragen des Korrosionsschutzes durch Anstrichstoffe

Problems of Interest in the Protection against Corrosion Using Coating Agents Within the scope of this review the protective coating of steel as well as galvanized constructions have been dealt with. Starting with the economical loss due to corrosion, as exemplified by a few cases of damage experienced in the practice, the following topics have been treated: Relationships between the condition of the surface and the quality of coating; cleaning and derusting; methods for application of the coating; (brushing, spraying); influence of environmental conditions; attainable and required thickness of the layer; criteria for evaluation (cost and durability); multi-layer systems; thick-layer coatings; coatings on zinc layers; temporary protection against corrosion (protection of rolled steel); protection against corrosion by desirable coating procedures.     

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.     

Electrochemical synthesis and corrosion performance of poly(pyrrole-co-o-anisidine)

The electrochemical synthesis of poly(o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole:o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly(o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly(o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.     

Electropolymerized bilayer coatings of polyaniline and poly(N-methylaniline) on mild steel and their corrosion protection performance

Polyaniline (PANI) and poly(N-methylaniline) (PNMA) have been electrodeposited on mild steel from oxalic acid bath using cyclic voltammetric technique. Pretreatments like passivation and primer polymer coatings were required for effective coating. Differently stacked composite polymer layers on the metal surface by layer-by-layer approach have also been obtained and their properties have been compared with their corresponding copolymer coatings. FTIR study confirms the formation of electroactive polymer compounds on mild steel. Evaluation of these coatings in 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy reveals significant corrosion resistant behavior. Relatively higher corrosion protection is exhibited by copolymer coatings and composite-bilayer coatings than the corresponding homopolymer coatings. The composite metal–PANI–PNMA layer shows higher stability and better protection than the metal–PNMA–PANI layer.     

Enhancing corrosion resistance of aluminum composites in 3.5% NaCl using pigmented epoxy fluoropolymer

The corrosion protection performance of AA6061 T6–10% Al₂O₃ composite, coated with four different fluoropolymer paint systems, were investigated in 3.5% NaCl aqueous solutions under uniform and scratched conditions. A comparison between epoxy-treated clear and pigmented fluoropolymer coatings with newly developed vanadate-based fluoropolymer coatings was performed from corrosion protection, adhesion and durability points of view. The corrosion rates of epoxy-treated clear FLBZ 1074 increased dramatically after less than one month of exposure in 3.5% NaCl aqueous solutions. The addition of iron oxide or titanium oxide as pigments to the fluoropolymer decreased the porosity of epoxy and hence, improved the corrosion resistance. The newly developed vanadate based-clear FLBZ 1074 system showed outstanding corrosion resistance even after two months of immersion in 3.5% NaCl aqueous solutions under scratched coating conditions. The durability of such new coating based on salt spray test results was very promising (>2000 h without any sign of corrosion). The vanadate-pigmented FLBZ 1074 showed a dramatic increase in the corrosion rates. Moreover, the presence of pigments affected negatively the adhesion performance as well as the durability of the coating. A general model has been used to analyze the impedance data in terms of reactions occurring during the interaction of the coated metal with the environment. It was found that the vanadate-treated specimens not only improve the protective power against filiform corrosion as a factor of time, but also maintain the adhesion performance within the acceptable ranges.     

Ni–W coatings electrodeposited on carbon steel: Chemical composition, mechanical properties and corrosion resistance

Hard, ductile and adherent nanostructured Ni–W coatings were electrodeposited on carbon steel from electrolyte solutions containing sodium tungstate, nickel sulfate and sodium citrate, using different current pulse programs. Current pulse frequency was the dominant factor to define chemical composition, grain size, thickness and hardness. According to the electrodeposition conditions the deposited coatings showed 15–30 at% W, the grain size ranged from 65 to 140 nm, and the hardness varied from 650 to 850 Hv. Tungsten carbide also present in the coating contributed to its hardness. The corrosion resistance of the Ni–W coated steel was tested by potentiodynamic polarization in a neutral medium containing sulphate ions. The Ni–W coating protected the carbon steel from localized corrosion induced by sulphate anions.     

Electrochemical study of tailored sol–gel thin films as pre-treatment prior to organic coating for AZ91 magnesium alloy

The behaviour/resistance of four optimised sol–gel coating systems (inorganic, hybrid organic–inorganic, containing zirconium ions and containing cerium ions) against corrosion of AZ91 magnesium alloy were studied. The coatings obtained by the sol–gel process were evaluated as autonomous protective coatings as well as a pre-treatment prior to acrylic top coat. The coating obtained from tetramethoxysilane (TMOS) and diethoxydimethylsilane (DEDMS) as precursors and doped with Ce³⁺ was especially effective as pre-treatment for a final acrylic coating. For non-defected coating the impedance modulus has not changed during the time of immersion (7 days) in 0.5 M Na₂SO₄. An inhibition of coating delamination at the defect of the acrylic coating was recorded by means of LEIS.     

Preparation of hybrid silica sol–gel coatings on mild steel surfaces and evaluation of their corrosion resistance

Hybrid silica sol–gel coatings were prepared on mild steel substrate by dip coating technique. The coatings were subsequently heat treated at 200 °C in order to improve their corrosion properties. The coating sols were synthesized using Glycidoxypropyltrimethoxysilane (glymo) and Aminopropylethoxysilane (ameo) as precursor materials. Potentiodynamic polarization curves were derived and Electrochemical Impedance Spectroscopy (EIS) measurements were made in NaCl solution. The surface and cross-section morphology of coated specimens were characterized by scanning electron microscopy (SEM). Fourier transformed infrared (FTIR) analysis was used to identify the presence of various functional groups in the coating solutions. A comparison of the corrosion resistance of the coated and uncoated mild steel was presented. The results indicated that the corrosion resistance of the coated mild steel was improved considerably.     

Anticorrosion efficiency of zinc-filled epoxy coatings containing conducting polymers and pigments

The dependence of the corrosion-inhibiting properties of zinc-filled organic coatings on the nature of the conducting polymers and conducting pigments added and on the pigment particles’ surface coating with conducting polymer layers were investigated. The following materials were selected to examine the corrosion-inhibiting properties of the conducting polymers: polyaniline phosphate (PANI), polypyrrole (PPy), natural graphite, and carbon nanotubes. Conducting pigment combinations for application in coating materials were formulated by applying pigment volume concentrations (PVC) of 0.3%, 0.5% and 1%, which were completed with Zn dust to obtain pigment volume concentrations/critical pigment volume concentrations (PVC/CPVC) = 0.64. Such conducting pigment/zinc dust combinations represented corrosion inhibitors to be used as ingredients in protective coatings. Solvent-based 2K epoxy resin based coating materials containing the corrosion inhibitors so formulated were prepared to examine their anticorrosion properties. The pigmented coatings were subjected to laboratory corrosion tests in simulated corrosion atmospheres and to standardized mechanical resistance tests. The protective coatings so obtained exhibited a higher efficiency than coating materials containing zinc dust alone. The coating material containing carbon nanotubes at PVC = 1% and the coating material containing graphite coated with polypyrrole (C/PPy) at PVC = 0.5% emerged as the best zinc-filled coating materials with respect to their corrosion-inhibiting efficiency. Treatment with the conducting polymers had a beneficial effect on the coating materials’ mechanical properties.     

Characterization of sol–gel coated 316L stainless steel for biomedical applications

Silica based organic–inorganic hybrid coatings were deposited on 316L stainless steel by sol–gel technique. The hybrid sols were prepared by hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane (TMSM) and tetraethylorthosilicate (TEOS) at different molar ratios. Electrochemical experiments were performed to evaluate the corrosion resistance properties of the coatings. Structural characterization of the coatings was performed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Contact angle measurement and cell morphology assay were performed to investigate the hydrophilicity and in vitro cytotoxicity of the coatings, respectively. The results indicate formation of a crack-free and highly adherent film acting as a protective barrier against the physiological medium. Corrosion resistance of hybrid coatings was influenced by the molar ratios of TMSM:TEOS. The best corrosion protection was obtained at TMSM:TEOS molar ratio of 1:1. Sol–gel coatings enhanced the hydrophilicity of 316L steel surfaces. Also, these coatings showed non-toxicity for L929 cells.     

Electrosynthesis of polyaniline–molybdate coating on steel and its corrosion protection performance

Electrosynthesis of polyaniline–molybdate (PANI–MoO₄²⁻) on mild steel was achieved in oxalic acid medium using cyclic voltammetry technique. Adherent and homogeneous PANI–MoO₄²⁻ coating was obtained. The corrosion behavior of steel with PANI–MoO₄²⁻ coatings in 1% NaCl solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The coating was characterized by SEM, XPS, EDAX and FTIR. The self-healing ability of PANI–MoO₄²⁻ coating was confirmed by SVET technique. It has been found that the PANI–MoO₄²⁻ coating is able to offer higher corrosion protection in comparison to that of pure PANI coating due to inhibitive nature of molybdate ions.     

Corrosion and mechanical behavior of fusion bonded epoxy (FBE) in aqueous media

In recent years there have been many reported cases of corrosion failure in cement concrete pipelines. In the majority of cases, the failures have been attributed to rebar corrosion which is caused by the permeability of chloride from low resistivity soil and subsequent attack on a passive layer on an iron bar in the structure. As a possible alternative to cementitious materials, some organic coatings based on olefin, vinyl or epoxy-based polymers have been considered. However, due to a paucity of data on the behavior of these coatings in aqueous media— particularly product water—the possibility of their application in water transmission systems in the Kingdom has not been fully exploited. This paper deals with the studies carried out on the corrosion and mechanical behavior of fusion bonded epoxy (FBE) coating on steel in aqueous media which include product water, distilled water and saline water. The mechanical testings on coating include adhesion, bending and cathodic disbondment testings. The corrosion studies include immersion testing under static and dynamic conditions, autoclave tests and accelerated (salt-fog) tests. The analysis of results indicates chemical inertness of FBE coating in either of the aforementioned water used during testing, good adhesion and no damage to the coating during bending. Cathodic disbondment tests indicate that FBE coating sustains under cathodic protection (CP) conditions. In general, the results of mechanical and corrosion tests indicate that FBE is a promising material for internal coating on steel in water transmission systems.     

Corrosion protection coating containing polyaniline glass flake composite for steel

Corrosion protection of steel by glass flake (GF) containing coatings is widely used in marine atmosphere. Even though, the coatings containing glass flake are highly corrosion resistant, their performance is decreased due to the presence of pinholes and coating defects. It is well established that polyaniline containing coating is able to protect the pinhole defects in the coatings due to passivating ability of polyaniline. Hence a study has been made on the corrosion protection ability of steel using polyaniline-glass flake composite containing coating with 10% loading of glass flake in epoxy binder. The polyaniline glass flake composite (PGFC) was synthesized by chemical oxidation of aniline by ammonium persulphate in presence of glass flake. The corrosion protection ability of GF and PGFC containing coating on steel was found out by salt spray test and EIS test in 3% NaCl. In both the tests, the resistance value of the PGFC containing coating has remained at 10⁸-10⁹ Ω cm² where as for the GF containing coating, the resistance values decreased to 10⁵ Ω cm². The enhanced corrosion protection ability of the PGFC containing coating is due to the passivation ability of the polyaniline present in the coating.     

Corrosion resistant behaviour of PANI–metal bilayer coatings

The present work discusses on the corrosion resistant behaviour of polymer metal bilayer coatings, viz. polyaniline (PANI), polyaniline–nickel (PANI–Ni), nickel–polyaniline (Ni–PANI), polyaniline–zinc (PANI–Zn) and zinc–polyaniline (Zn–PANI). The coatings were synthesized by means of cyclic voltametric method. The coatings thus obtained were uniform in nature and highly adherent to the mild steel substrate. The effectiveness of the coatings in preventing corrosion was tested by electrochemical impedance studies (EIS) using Nyquist and Bode plots and potentiodynamic polarization studies as well. Among the various coatings synthesized, the PANI–Zn coating was found to offer the maximum protection, followed by PANI–Ni coatings. Metal–PANI coatings were found to offer the least resistance to corrosion. The coatings thus obtained were characterized by scanning electron microscopic (SEM) analysis and the results are discussed.     

Micro-abrasion–corrosion interactions of Ni–Cr/WC based coatings: Approaches to construction of tribo-corrosion maps for the abrasion–corrosion synergism

The process of micro-abrasion–corrosion has been the subject of much research in recent years due to the fact that the action of micron sized particles, typically less than 10 μm in diameter, can cause significant degradation of materials in many diverse environments involving aqueous corrosion. Cermet based coatings are often used to combat micro-abrasion–corrosion, but there has been little work carried out to characterize the performance of such coatings exposed to micro-abrasion–corrosion or to provide a basis for coating optimisation. In addition, a basis for defining the various micro-abrasion–corrosion interactions has not been suggested to date.In this study, the micro-abrasion–corrosion performance of a Ni–Cr/WC coating was assessed and compared to the performance of the steel substrate. The results were used to identify regimes of micro-abrasive wear as a function of applied load and pH of the solution. In addition, micro-abrasion–corrosion maps were constructed based on the results, showing the variation between micro-abrasion–corrosion regimes, as a function of applied load and pH of the solution.