Low temperature deposition of dense MnCo2O4 protective coatings for steel interconnects of solid oxide cells

In this work manganese cobalt spinel (MnCo₂O₄) coatings were deposited on steel substrates by spray pyrolysis at 390?°C. This is at much lower temperatures than previously reported (typically in excess of 900?°C). It was possible to produce coatings with well controlled thickness (2-5-10?μm). The as-deposited coatings were evaluated for their microstructural changes and electrical conductivity up to 800?°C. Results confirm the formation of a single phase spinel with high density and electrical conductivity. Based on the obtained results, it might be concluded that spray pyrolysis is a very promising method to develop protective coatings for steel substrates at low temperatures overcoming limitations of many other methods.     

Sol–gel coatings on metals for corrosion protection

Sol–gel protective coatings have shown excellent chemical stability, oxidation control and enhanced corrosion resistance for metal substrates. Further, the sol–gel method is an environmentally friendly technique of surface protection and had showed the potential for the replacement of toxic pretreatments and coatings which have traditionally been used for increasing corrosion resistance of metals. This review covers the recent developments and applications of sol–gel protective coatings on different metal substrates, such as steel, aluminum, copper, magnesium and their alloys. The challenges for industrial productions and future research on sol–gel corrosion protective coatings are also briefly discussed.     

Effect of introduction of structural defects on protective ability of polyesters

Permeability of a polymer plays an important role in conferring the protective ability of organic coating to the steel surface against atmospheric corrosion. Although the relationship between structure of polymers and their permeability has been extensively studied in various applications like membranes, packaging, etc., such detailed study is lacking in the area of coatings. The systematic study of structure–permeability relationship of polymers in clear coatings can give guidelines in selecting the binder for the required application. This article deals with the effect of introduction of structural defects into a straight chain aliphatic polyesters on the protective ability of their clear coatings against corrosion. The mild steel panels coated with clear coatings based on the polyesters were exposed to humidity in humidity chamber. A novel technique of detecting the onset of corrosion was used instead of conventional methods that detect the failure of the coating due to corrosion. It was observed that even at 1–10% mole defect introduced by replacement of straight chain diols with branched diols, the protective ability of clear coatings was affected drastically.     

The influence of aluminium surface pretreatment on the corrosion stability and adhesion of powder polyester coating

One of the most important factors in corrosion prevention by protective coatings is the coating adhesion loss under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In order to improve the adhesion of organic coating the metal substrate is often pretreated in some way. In this work, the adhesion of polyester coatings on differently pretreated aluminium surface (by anodizing, with and without sealing, by phosphating and by silane film deposition) was examined. The dry and wet adhesion of polyester coatings were measured by a direct pull-off standardized procedure, as well as indirectly by NMP test. It was shown that under dry test conditions all polyester coatings showed very good adhesion, but that aluminium surface pretreated by silane film showed superior adhesion. The overall increase of wet adhesion for polyester coating on aluminium pretreated by silane film was maintained throughout the whole investigated time period. The different trends in the change of adhesion of polyester coatings were observed for different aluminium pretreatments during exposure to the corrosive agent (3% NaCl solution). The highest adhesion reduction was obtained for polyester coating on aluminium pretreated with phosphate coating. The corrosion stability of polyester coated aluminium was investigated by electrochemical impedance spectroscopy in 3% NaCl solution. The results confirmed good protective properties of polyester coating on aluminium pretreated with silane film, i.e. greater values of pore resistance and smaller values of coating capacitance were obtained in respect to other protective systems, whereas charge-transfer resistance and double-layer capacitance were not measurable during 2 months of exposure to a corrosive agent.     

Electroplated bright aluminium coatings for anticorrosion and decorative purposes

This paper is dedicated to the study of electrodeposited aluminium layers as anticorrosion protective coatings on metallic substrates. The aim of this approach is to propose a non-toxic alternative to the traditional nickel–chromium coating, for anticorrosive and decorative purposes. Aluminium was electrodeposited on carbon steel substrates from chloroaluminate based ionic liquids with and without the addition of 1,10-phenantroline. In the first case, the Al deposits are dense but dull, while in the latter homogeneous and bright coatings suitable for decorative purposes were achieved.     

Sulfonation of base oils as corrosion inhibitor for temporary protection of steel in atmospheric environment

Base oil corrosion temporary protective coatings were synthesized. These coatings contain of inhibitor agent, antioxidant agent, and base oil as main bed. Inhibitor agents were prepared by sulfonation of Iran traditional mineral base oils. Iran traditional base oils were SAE10, SAE30 and SAE40. They are sulfonated at different temperatures with oleume as reactive agent. Sulfonation efficiency and production quality of this process are evaluated in different conditions. Neutralization of sulfonate groups were complied with calcium hydroxide to achieved hydrophilic salt groups of calcium sulfonate. Final products are used as inhibitor agents in base oils to prepare temporary protective coatings. They are applied to 1020 steel panels by dipping method.     

Steel corrosion in simulated carbonated concrete pore solution its protection using sol–gel coatings

The corrosion features of polysiloxane hybrid films deposited on carbon steel substrates by dip-coating are compared. Sol–gel coatings were prepared by condensation and polymerization of TEOS/MPTS, TEOS/MTES, TMOS/MPTS and TMOS/MTES mixtures in three molar ratios to assess the influence of their components. The corrosion protection of the coatings was evaluated by means of polarization curves and electrochemical impedance spectroscopy measurements. Coating thickness and composition were quantified by field emission scanning electron microscopy equipped with an EDX analyzer. The results show that all the coatings improved the corrosion resistance of carbon steel in a carbonated synthetic solution, with especially improved protective properties in the case of the TMOS/MTES mixture. These best properties could be due to a highly cross-linked network and greater adhesion to the metallic surface, restricting the corrosion attack.     

Evaluation of the corrosion resistance of phosphate coatings obtained by anodic electrochemical treatment

The corrosion resistance of phosphate coating obtained by anodic electrochemical treatment at 4–6 mA/cm² is addressed in this paper. The corrosion performance of these coatings is also compared with the coatings obtained by chemical treatment. The regenerated phosphoric acid under the influence of anodic current causes a large variation in morphological features of the coatings. Immersion and salt spray tests indicate the ability of these coatings to act as a barrier film on mild steel. Polarization and electrochemical impedance spectroscopic (EIS) studies indicate that the corrosion resistance of phosphate coatings obtained by anodic treatment decreases with increase in current density employed for deposition. In spite of their higher coating weight, the corrosion resistance of phosphate coatings obtained by anodic treatment is inferior to those obtained by chemical treatment. The porosity or discontinuities created due to the dissolution of the coating under the influence of anodic current are considered responsible for the inferior corrosion resistance of these coatings. The study concludes that anodic treatment has only a limited scope for preparing phosphate coatings with improved corrosion resistance.     

Effect of Al and Ag dopants on the corrosion resistance of the AISI 316L-YSZ system

We present results for the deposition of coatings of zirconium stabilized with Yttria (YSZ) and doped with aluminum and silver. The coatings were grown from an YSZ ceramic target symmetrically covered with metallic (Al, Ag) pieces on AISI 316L steel substrates, via the RF sputtering technique. The microstructure of the coatings was characterized by means of X-ray diffraction (XRD), the chemical composition was determined through X-ray dispersive energy (EDX) analysis, and the electrochemical response was evaluated via impedance (EIS) and Tafel corrosion techniques. The XRD analysis showed that the coatings exhibited peaks belonging to the target material, dopant elements, and oxides such as Al₂O₃. Electrochemical analysis indicated an increase in the corrosion resistance of the coatings grown on aluminum oxide.     

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.     

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.     

Development of novel waterborne poly(1-naphthylamine)/poly(vinylalcohol)–resorcinol formaldehyde-cured corrosion resistant composite coatings

Advancements in the field of corrosion protective coatings have headed towards the utilization of conducting polymer-based blends and composites for the formulation of corrosive protective paints and coatings. With the aim to develop an ecofriendly waterborne conducting polymer-based protective coating material, corrosion protective behavior of waterborne resorcinol formaldehyde (RF)-cured composite coatings of poly(1-naphthylamine) (PNA)/poly(vinylalcohol) (PVA) was investigated on mild steel (MS). The corrosion protective performance was evaluated by physicochemical, physicomechanical, corrosion protective efficiency and resistance in acid, alkaline and saline media by open circuit potential (OCP) measurements. The morphologies of coated, uncoated as well as corroded samples were analyzed by SEM technique. Superior corrosion protective performance was observed which was compared to the reported solvent-based conductive polymer coatings in different corrosive media.     

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.     

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.     

Electrochemical assessment of the self-healing properties of Ce-doped silane solutions for the pre-treatment of galvanised steel substrates

The present work aims at assessing the electrochemical behaviour of galvanised steel (GS) substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) doped with cerium nitrate. Furthermore, the work aims at evaluating the self-healing properties of the dopant and discussing the possible mechanisms involved in this process. The study was performed by electrochemical impedance spectroscopy (EIS) and by the scanning vibrating electrode technique (SVET), during immersion in NaCl solutions. X-ray photoelectron spectroscopy (XPS) was also used to complement the electrochemical results. The results show that the protective behaviour of the pre-treatments based on Ce-doped silane solutions is dependent on the concentration of the dopant. The results also show that the dopant improves the anti-corrosion performance of the silane coatings formed on galvanised steel substrates.     

Mechanisms of non-toxic anticorrosive pigments in organic waterborne coatings

Investigations have been carried out concerning the mechanism of the behaviour of non-toxic anticorrosive pigments belonging to the group of phosphates, ferrites and ion exchange pigments in waterborne systems. The mechanism controlling the protective effectiveness of organic coatings is complex and results from simultaneous activity of various agents, from among which the kind of the corrosion inhibitor and the structure of the coating are of fundamental importance. The effect of pigments on the protective properties of coatings was tested by means of electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) as well as the salt spray and Prohesion tests. For the investigation of the structure of coatings the porosymetric method and modulated-force thermomechanical analysis (mf TMA) were applied. The results of these investigations have shown that calcium zinc phosphate and zinc ferrite are the most effective. These pigments take part in the passivation of steel, which has been proved by the results of electrochemical investigations and by the presence of the passive layers as has been found out by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDXA) and scanning electron microscopy (SEM). Calcium zinc phosphate and zinc ferrite affect the structure of the coatings, increasing the glass transition temperature (Tg) of the coatings. Zinc phosphate and calcium-exchanged silica do not act in compliance with electrochemical mechanism neither do they improve the barrier properties of the binder.     

Corrosion resistance of phosphate coatings obtained by cathodic electrochemical treatment: Role of anode–graphite versus steel

The formation of phosphate coatings by cathodic electrochemical treatment using graphite and steel anodes and evaluation of their corrosion resistance is addressed in this paper. The type of anode used, graphite/steel, has an obvious influence on the composition of the coating, resulting in zinc–zinc phosphate composite coating with graphite anode and zinc–iron alloy–zinc phosphate–zinc–iron phosphate composite coating with steel anode. The corrosion resistance of the coating is found to be a function of the composition of the coating. The deposition of zinc/zinc–iron alloy along with the zinc phosphate/zinc and zinc–iron phosphate using graphite/steel anodes has caused a cathodic shift in the E_corr compared to uncoated mild steel substrates. The i_corr values of these coatings is very high. EIS studies reveal that zinc/zinc–iron alloy dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the formation of zinc and iron corrosion products imparts resistance to the charge transfer process and increases the corrosion resistance with increase in immersion time. The corrosion products formed might consist of oxides and hydroxychlorides of zinc and iron. The study suggests that cathodic electrochemical treatment could be effectively utilized to impart the desirable characteristics of the coating by choosing appropriate anode materials, bath composition and operating conditions.     

Multilayer architecture design to enhance load-bearing capacity and tribological behavior of CrAlN coatings in seawater

Steel materials employed in severe conditions including strong corrosion, high load and multi-factor coupling damages can easily cause incredible degradation until failure, and the protective CrN-based coatings should be one of promising candidates to relieve those damages for the steel equipment or components. In present paper, the monolayer CrAlN and multilayer Cr/CrAlN coatings were successfully deposited on steel substrates by multi-arc ion technology, and their microstructure, mechanical, tribological and corrosion performances were systematically investigated. The results show that the special multilayer Cr/CrAlN coating could possess much better load-bearing capacity and wear resistance than that of monolayer CrAlN coating, which was due to the facts that the multilayer architecture can effectively release the internal stress and inhibit the expansion of defects. Particularly, the multilayer interfaces could effectively prevent the aggressive medium in seawater infiltrating into the inside of coating, and thus the multilayer Cr/CrAlN coating could have higher corrosion resistance compared to monolayer CrAlN coating. As a result, this multilayer Cr/CrAlN coating could achieve excellent combined performances, indicating that it has greatly potential application as protective coating in seawater.     

Green chemistry in situ phosphatizing coatings

The current organic coating on metals for aerospace applications involves a multi-step process and considerable energy, labor and control, and it generates toxic wastes such as chlorinated solvents, cyanide, cadmium, lead and carcinogenic chromates. The green chemistry technology of in situ phosphatizing coatings (ISPCs) developed in our laboratory is a one-step self-phosphating process, in which the deposition of metal phosphate layer on the substrate surface and the curing of polymer paint film take place independently, but simultaneously. The formation of a metal phosphate layer in situ will essentially eliminate the metal surface pre-treatment step of employing a phosphating line/bath. The use of chemical bonds linked to the paint polymers to seal the pores of metal phosphate in situ should enhance coating adhesion and suppress metal corrosion without a post-treatment of final rinses containing chromium (Cr⁶⁺). The successful applications of ISPCs in three types of commercial paints (solvent-borne high-solids, water-reducible and VOC-free latex) on bare and pre-treated cold-rolled steel and 2024 aluminum coupons is presented. The protective performance (coating adhesion and corrosion inhibition) of ISPCs is shown to be superior over that of the current multi-step coating practice.     

Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution

The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1 M sulfuric acid solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm⁻². Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1 M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.