Corrosion Protection Strategies Research Articles

Cerium oxide loaded with Gum Arabic as environmentally friendly anti-corrosion additive for protection of coated steel

The depreciation of assets and safety threats because of corrosion has forced to develop eco-friendly and smarter corrosion protection strategies. In this study, natural Gum Arabic (GA) was used as a corrosion inhibitor and loaded into cerium oxide nanoparticles (CONPs) to develop an environment-friendly additive for corrosion protection of coated steel in the marine environment. This additive was uniformly dispersed into an epoxy formulation that was used to protect steel plates. Epoxy coatings containing CONPs, without GA, were also prepared as reference. High-Resolution Transmission Electron Microscopy (HR-TEM) and Fourier Transform infrared spectroscopy (FTIR) revealed the successful loading of GA into the CONPs. Thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) techniques confirmed approximately ⁓30.0 wt% loading of GA into the CONPs. Electrochemical impedance spectroscopy (EIS) demonstrated the anticorrosion properties of the epoxy coatings modified with the GA loaded CONPs when compared to reference coatings. The corrosion protection mechanism postulates that GA loaded CONPs act as a filler material for epoxy coating and it can also aid the recovery of the protective properties of the epoxy coating leading to the formation of a stable protective layer.

Responsive Colloidosomes with Triple Function for Anticorrosion.

Strategies for corrosion protection are required to prolong the life span of metallic structures used by the construction, aerospace, and transport industries. Currently, there are no coatings that can provide at the same time information about the corrosion status of the coated metal and protect the metal against corrosive species and mechanical damage. Herein, triple-functional microcarriers with functions of corrosion sensing, self-healing, and corrosion inhibition are produced and embedded in coatings to prolong the lifetime of metals and enhance the anticorrosion performance of coatings. The microcarriers are prepared by creating Pickering droplets loaded with a corrosion inhibitor and a healing agent and stabilized by silica nanocapsules containing thymol blue as corrosion sensor. The microcarriers are then embedded in a water-based polymer matrix coated on metal substrates. When the coating or metal is mechanically damaged, the healing agent is released from the droplets to hinder further corrosion of the metal. When the local pH value near the metal surface is changing by the generation of hydroxide ion due to the corrosion process, a change of color is detected as well as a release of corrosion inhibitor, leading to a significant decrease of corrosion rate of the coated metal.

Flash-PEO coatings loaded with corrosion inhibitors on AA2024

Flash plasma electrolytic oxidation (flash-PEO) with in situ incorporation of inhibitors is explored as a strategy for corrosion protection of 2024 aluminium (Al) alloys. Thin (~5 μm) and energy-efficient coatings were successfully developed on the Al substrate in 100 s treatment time using different electrolytes based on molybdate, stannate, tungstate, vanadate lanthanum or cerium salts additives with and without complexing agent (EDTA). Screening of the optimum combination in search of minimum thickness and best corrosion protective performance was performed using electrochemical impedance spectroscopy (EIS). Coatings based on EDTA-Ce and WO42 were selected and investigated further in comparison with the inhibitor-free phosphate coating in terms of morphology, composition, corrosion behaviour and paint adhesion. EDTA-Ce coating showed excellent paint adhesion and the highest impedance modulus at short immersion times in 3.5 wt% NaCl aqueous solution. Neutral salt spray testing of this coating as a full system comprising an epoxy primer showed no signs of corrosion after 1000 h of exposure.

Adsorption and Diffusion Moderated by Polycationic Polymers during Electrodeposition of Zinc.

Electrodeposition of metals is relevant to much of materials research including catalysis, batteries, antifouling, and anticorrosion coatings. The sacrificial characteristics of zinc used as a protection for ferrous substrates is a central corrosion protection strategy used in automotive, aviation, and DIY industries. Zinc layers are often used for protection by application to a base metal in a hot dip galvanizing step; however, there is a significant interest in less energy and material intense electroplating strategies for zinc. At present, large-scale electroplating is mostly done from acidic zinc solutions, which contain potentially toxic and harmful additives. Alkaline electroplating of zinc offers a route to using environment-friendly green additives. Within the scope of this study an electrolyte containing soluble zinc hydroxide compound and a polyquarternium polymer as additive were studied during zinc deposition on gold model surfaces. Cyclic voltammetry experiments and in-situ electrochemical quartz crystal microbalance with dissipation (QCM-D) measurements were combined to provide a detailed understanding of fundamental steps that occur during polymer-mediated alkaline zinc electroplating. Data indicate that a zincate-loaded polymer can adsorb within the inner sphere of the electric double layer, which lowers the electrostatic penalty of the zincate approach to a negatively charged surface. X-ray photoelectron spectroscopy also supports the assertion that the zincate-loaded polymer is brought tightly to the surface. We also find an initial polymer depletion followed by an active deposition moderation via control of the zincate diffusion through the adsorbed polymer.

The effects of an inorganic corrosion inhibitor on the electrochemical behavior of superhydrophobic micro-nano structured Ni films in 3.5% NaCl solution

The application of hierarchically micro-nano structured superhydrophobic Ni films with increased surface roughness is known as an attractive corrosion protection strategy because the chemically modified film with a low surficial free energy is capable of keeping water molecules and aggressive species away from the coating/electrolyte interface by trapping air pockets within the micro-nano structured layer. Furthermore, corrosion inhibitors are widely used for corrosion mitigation in a broad range of industrial applications. This study tends to investigate the corrosion resistance of electrodeposited superhydrophobic Ni films in the presence of sodium molybdate (0 M, 0.03 M, 0.06 M, 0.1 M) as an inorganic corrosion inhibitor in a 3.5 wt% NaCl solution at 25 °C, up to 120 h. The micro-nano structured superhydrophobic Ni film with a mean thickness of 4 μm was electrodeposited on a Cu substrate via a two-step electrodeposition process at 60 °C including 8 min of electrodeposition at a constant current density of 20 mA/cm2, followed by 1 min of electrodeposition at a constant current density of 50 mA/cm2 and a subsequent chemical modification step in stearic acid solution.Investigation of surface topography of the film by atomic force microscopy technique (AFM) revealed that the root-mean-square of height and the skewness of the film were equal to 14.4 nm and 0.21, respectively. The morphology of the film consisted of micro-nano cones in the size range of 50 to 1000 nm. The superhydrophobic film demonstrated a passivation behavior and a pitting potential. The EIS study identified the Ni film as a non-ideal capacitor and an equivalent circuit model with two parallel time-constants fitted to the EIS data. Upon 120 h of immersion of the superhydrophobic film in the electrolyte in the presence of 0.1 M of sodium molybdate, the corrosion inhibitor efficiency of about 80% was achieved and the Ni film demonstrated the best passivation behavior and the lowest corrosion current density.

A new strategy for corrosion protection of porous stainless steel using polypyrrole films

In this work, a method to improve the protection against corrosion of porous sintered stainless steel is presented. It is based on the electrodeposition of polypyrrole (PPy) layers doped with a large size counterion such as dodecylbenzenesulphonic acid (DBSA), a conducting polymer with high corrosion resistance and good biocompatibility. The efficacy of PPy coating depends on the adequate adhesion between the metal substrate and the coating layer. The protection against corrosion has been tested using 316 L stainless steel (SS) powder sintered at different conditions to evaluate the effect of the sintering atmosphere (nitrogen and vacuum) and cooling rates (furnace and water) on corrosion resistance, while wrought 316 L SS has been used as reference material. In addition, two electrochemical deposition techniques have been tested to select the most adequate. Open circuit potential evolution, anodic polarization measurements and electrochemical impedance spectra have been used to evaluate corrosion protection in phosphate buffer saline medium. It has been evidenced that a more homogeneous and stable coating was obtained in the case of porous stainless steel. The corrosion potential shifted to nobler values and the anodic polarization branch became more stable. Coated porous samples have a good passivation performance with a lower stable passive current density and a higher breakdown potential. The transfer electronic resistance and the impedance module increase more than one order of magnitude. Therefore, the porosity of sintered stainless steel is seen as an advantage for the improvement of the adherence of the PPy coatings. The best corrosion protection is found for samples sintered in nitrogen and water-cooled.

Recent Development of Corrosion Protection Strategy Based on Mussel Adhesive Protein

Many of traditional anti-corrosion approaches using chromate are effective but hazardous to natural environment and human health, so development of green and effective alternatives is desirable. One of the mussel adhesive proteins derived from mussel byssus presents extraordinary adhesion to steel surface and exhibits film-forming and corrosion inhibition properties. Novel strategies for enhancing the corrosion inhibition of steel by the protein have been demonstrated recently. The protein together with ceria nanoparticles presents a great potential for the development of new corrosion inhibitors and thin films that are ‘green’ and ‘effective’, and have ‘smart’ protection properties.

Effect of nano-zerovalent iron incorporated polyvinyl-alginate hybrid hydrogel matrix on inhibition of corrosive bacteria in a cooling tower water environment

Microbial-induced corrosion (MIC) is an insidious process caused by microbial growth on metals. Among many metals, aluminium, brass, mild steel, stainless steel and carbon steels are more vulnerable to MIC. The present study investigates one of the effective corrosion protection strategies using hybrid hydrogel coating. In this regard, the anti-corrosive activity of n-zerovalent iron (nano-ZVI) incorporated polyvinyl-alginate (PVA) hybrid hydrogel-coated matrix against MIC on aluminium, Al 1100 metal, was tested. The study was conducted against corrosion-inducing bacteria, Terribacillus aidingensis EN3 (Accession number: KR183874), isolated from cooling tower water system. The antibacterial results of nano-ZVI showed a diameter of zone of inhibition at 10 mg/mL. Hybrid hydrogel matrix was employed against the MIC in cooling tower water-containing systems, I, II and III, IV along with a control. The results of the study were supported with weight loss (WL) analysis and electrochemical impedance spectroscopy (EIS) studies. WL results showed a reduced rate of 0.08 mm/y corrosion in hybrid hydrogel system than the other systems. The EIS studies showed higher charge transfer resistance (Rct) of 14.53 Ω and solution resistance of 3.8 Ω. These results confirmed the presence of nano-ZVI in hybrid hydrogel acted as an antibacterial agent in the PVA-alginate protective film against corrosion in Al 1100. Thus, the obtained results evidenced the novel idea of hydrogel matrix to act as an anti-corrosive film in the cooling tower system.

Strategies for corrosion protection of non-ferrous metals and alloys through surface engineering

Abstract In the modern world, surface engineering technologies have been playing an important role to overcome in-service degradation of ferrous and non-ferrous materials. In this context, the primary objective of this article is to comprehensively review the corrosion behaviour of protective coatings deposited through different surface engineering technologies namely (a) Thermal spray techniques such as plasma spray, high velocity oxy-fuel spray, detonation spray and cold spray; (b) Electrolytic processes including anodizing, hard anodizing, hard chrome plating, electroplating, pulse electrodeposition and micro arc oxidation; (c) Physical vapour deposition techniques namely magnetron sputtering and cathodic arc; (d) sol-gel coatings; and (e) laser materials processing on a variety of non-ferrous materials. The process-structure-property-performance aspects of these coatings are critically reviewed which indeed was the basis for their industrial adaptation in textile, naval, automotive, aerospace, mobile communications, power generation, energy management, electronics and strategic sectors. The critical strategies and challenges associated with each processing technique and the resultant corrosion behaviour were highlighted. In addition, the future R&D direction in each of the aforementioned processes and materials were identified and discussed.

Macro-Encapsulation of Inorganic Phase-Change Materials (PCM) in Metal Capsules.

The design of phase-change material (PCM)-based thermal energy storage (TES) systems is challenging since a lot of PCMs have low thermal conductivities and a considerable volume change during phase-change. The low thermal conductivity restricts energy transport due to the increasing thermal resistance of the progressing phase boundary and hence large heat transfer areas or temperature differences are required to achieve sufficient storage power. An additional volume has to be considered in the storage system to compensate for volume change. Macro-encapsulation of the PCM is one method to overcome these drawbacks. When designed as stiff containers with an air cushion, the macro-capsules compensate for volume change of the PCM which facilitates the design of PCM storage systems. The capsule walls provide a large surface for heat transfer and the thermal resistance is reduced due to the limited thickness of the capsules. Although the principles and advantages of macro-encapsulation have been well known for many years, no detailed analysis of the whole encapsulation process has been published yet. Therefore, this research proposes a detailed development strategy for the whole encapsulation process. Various possibilities for corrosion protection, fill and seal strategies and capsule geometries are studied. The proposed workflow is applied for the encapsulation of the salt hydrate magnesiumchloride hexahydrate (MCHH, MgClHO) within metal capsules but can also be assigned to other material combinations.

Zinc Base Coatings, Their Challenges and New Strategies

Zinc based coatings are effective of protecting steel structures for various industrial applications due to their cathodic protection properties on top of the barrier protection. Hot dip galvanization was the most historical technique under this category. Despite of their historical background, using hot dip galvanization in some current applications has become questionable specially due to their inability to apply on site which reduces the productivity and adverse environmental consequences galvanization process may can cause. Zinc rich coatings trying to replace hot dip galvanization in these demanding applications though they have another set of industrial challenges to satisfy. One such a demand is to cater aesthetic requirements, to provide coloured coating without compromising corrosion protection properties. Current practice is to apply a multi coat system which may contain three or more layers. Thus, based on the critical service related problems of current zinc based coatings, this work is focused to develop processes to provide an effective and reliable zinc based corrosion protective coating system which satisfy aesthetic requirements, aiming building and construction related applications. To enhance the productivity compared to the current coating systems, it is expected to develop a single layer coloured zinc rich coating accommodating different corrosion protection strategies. Colouring pigment with suitable size distribution and chemical properties are studied for this development to fulfil the aesthetic purpose, while examining the effect of other additives to enhance the corrosion protection properties. Synergistic effect of different corrosion protection strategies is evaluated to review the suitability of the single colour zinc coating. Overall corrosion protection performance of the developed coatings is evaluated by methodologies based on scientific principles and international standards to get quantitative and qualitative details of coatings properties. Details of this development with evaluation results will be presented. Alternative solutions to cater industrial demands will also be discussed.

Fabricating robust and repairable superhydrophobic surface on carbon steel by nanosecond laser texturing for corrosion protection

In recent years, fabricating superhydrophobic surface has been deemed to be a promising strategy for metal corrosion protection. Here, a facile and simple nanosecond laser texturing treatment was proposed for constructing superhydrophobic surface on carbon steel. During the machining process, a series of circle-shaped texture patterns with different p/d values were directly fabricated on steel surfaces by nanosecond laser machine. According to the SEM images, the circle-shaped texture pattern showed desirable multimodal structure. When the laser textured steel surface was further chemically modified, it became superhydrophobic. With increasing the p/d value from 1.0 to 1.8, the superhydrophobicity of laser textured superhydrophobic steels deceased continually due to the increased undesirable flat area. Furthermore, the laser textured superhydrophobic steel also showed superb mechanical durability against abrasive damage. Owing to the excellent obstructive effect to corrosive medium, all the superhydrophobic steels displayed superior corrosion resistance in 3.5 wt% NaCl solution and the superhydrophobic steels with lower p/d values displayed better corrosion resistance. In addition, the laser textured superhydrophobic steel also showed desirable chemical stability and excellent healability even it lost its superhydrophobicity. It was also worth pointing out that a relatively higher drying temperature could further improve the chemical stability and enhances the corrosion protection, which made this process technique more promising and competitive for future practical applications.

Innovative Techniques/Technologies to Enhance the Durability of Civil Infra Structures PART 2: Corrosion Protection Techniques/ Technologies

Background: The durability of civil infrastructures is a severe problem faced by Scientists, Engineers and Technologies of 21st Century, due to the increasing pollution of our environments. This paper deals with innovative corrosion protection techniques/technologies to enhance the durability of civil infrastructures. Corrosion resistant rebars manufactured using Cu, P, Ni and Cr are capable of bearing the humid conditions of the coastal areas. TATA TISCON 500D rebars de-signed with diminished levels of impurities like S and P showed better corrosion resistance properties. Compared to CTD rebars, TMT rebars with tempered martensite zone showed improved corrosion re-sistance properties. Cement based coated steel rebars (inhibited cement slurry coated, cement polymer composite coated rebars) found to be more compatible for reinforcement corrosion control, in compari-son to galvinized and epoxy coated rebars. Fly ash, slag or silica fume, blended cements are finer as compared to OPC. The fineness reduced the permeability of blended cement concrete and improved the durability. Ternary blended cements, due to the fineness of the material and increased alumina, silica contents showed improved mechanical properties and better protection for steel in concrete. Owing to the unique molecular structure and high ion exchange capacity, chloride scavengers reduced the corro-sion susceptibility. Epoxy-polyurethane based surface coatings enhanced the durability as barrier type of coatings. Corrosion inhibiting admixtures such as calcium nitrite, citrate and stannate due to the for-mation of an insoluble film enhanced the corrosion resistance properties of reinforcements. Migrating corrosion inhibitors (MCI) based on amino alcohol, amines and nitrites showed superior corrosion resistance properties when compared to admixed inhibitor systems. Depending upon the environmental conditions, the implementation of corrosion protection technologies definitely enhanced the durability of civil infrastructures. Methods: The durability of the civil infrastructures such as National Highway Bridges, Nuclear Reactors, Elevated water tanks, On-shore and Off-shore concrete structures will be enhanced by adopting Innovative Corrosion protection Techniques/ Technologies such as i) Corrosion resistant rebars, ii)Coatings to steel rebars, iii) Blended cements, iv) Chloride scavengers for marine structures and v) Corrosion inhibiting admixtures for fresh structures. For existing structures, the following innovative technologies such as i). Coatings to concrete surface ii). Migrating corrosion inhibitors will be implemented. Results: After adopting the appropriate innovative corrosion protection techniques/technologies, the effect of treated structures will be monitored by conducting NDT techniques. Conclusion: Each and every innovative corrosion protection techniques/technologies have its own merits, demerits and limitations. Proper selection of method of corrosion protection strategies depending upon the environmental conditions can only lead to saving of money and enhancing the durability of civil infrastructures. In order to enhance the service life of civil infrastructures, it is essential to provide additional protective measures. Keywords: Protection strategies, corrosion resistant steel rebars, coatings to steel rebars, blended cements, admixtures, migrating corrosion inhibitors, chloride scavengers, repair/renovation strategy.

Development of self-healing coatings for corrosion protection on metallic structures

Inspired by biological systems, artificial self-healing materials are designed for repairing local damage caused by external factors. The rapidly expanding field of self-healing systems contains, among others, materials with well-defined surface properties. Undoubtedly, enhancing surface functionalisation, by applying smart coatings, enjoys an extensive interest. The self-healing ability is particularly essential property for corrosion protection strategies, especially when the use of one of the most effective corrosion systems, based on chromium(VI) compounds, is now banned by the current registration, evaluation, authorisation and restriction of chemicals legislation. Self-healing protective coatings are produced using macromolecular compounds, ceramics, metals and composites. Considering the wide range of available materials, the number of potential combinations seems to be unlimited. The self-healing action of such coatings is activated by appropriate stimuli: temperature changes, radiation, pH changes, pressure changes and mechanical action. In this paper, the research and practical implications of the various approaches to achieving self-healing functionality of protective coatings, as well as potential developments in this area, are explored.

Investigation of the Effectiveness of Repairs and Protection Materials / Techniques for Alleviating Durability Problems

Chloride-induced corrosion is one of the major forms of premature deterioration in Jordan, particularly in the industrial structures located in the Dead Sea Region, which is one of the most severe corrosive environments in the world. Significant forms of deterioration occurred within (10-15) years of the service life of the structures. Achieving the desired service life without expending excess funds for maintenance or rehabilitation is the objective of any designer. Proper attention to durability considerations in design can greatly extend the life of a structure. High quality and adequate cover provide the first line of defense against corrosion and should always be specified to assure durability. However, the experience of the research team has shown that relying solely on quality and cover as a corrosion-protection strategy may not assure long-term durability and protection against corrosion-induced damage. Concrete cracking and variations in materials and construction quality can undermine the effectiveness of concrete only protection strategies. This paper presents the outcomes of a 4-year duration research work conducted to evaluate the effectiveness of some selected repair and protection materials/ techniques that are available at the Jordanian market in alleviating the problem of chloride-induced corrosion, hence improving durability.

Corrosion issues in joining lightweight materials: A review of the latest achievements

Multimaterials assemblies and, in particular, assemblies made of lightweight components are of utmost relevance in many technical applications. These assemblies include multimetal, metal-polymer, metal-adhesive, and metal-composites combinations, among others. Presently, the transportation sector is looking for lighter materials that allow for reducing fuel consumption and the environmental footprint. Aluminum and magnesium alloys, as well as composites and polymers, are considered strategic for such purposes, and their joining in metal-metal or hybrid assemblies has been explored to develop lightweight components. These multimaterial assemblies are often exposed to aggressive environments in which moisture and aggressive species are present. Under these conditions corrosion phenomena are a major source of material failures. Depending on the nature of the metals and nonmetals and of the joining process, the mechanism and extent of corrosion can vary significantly. Thus, it is essential to understand the impact of corrosion in joined materials and to know which counter-measures can be adopted to mitigate corrosion events in the system of concern. This chapter aims at reviewing the latest results of studies focused in corrosion issues in the joining of lightweight materials. It describes the most common corrosion phenomena observed in joined materials, and it emphasizes corrosion issues in assemblies that combine different metals and that combine metals with nonmetals. Moreover, it overviews the state-of-the-art in corrosion protection strategies that can be applied and, finally, it overlooks the future trends.

A polyaniline based intrinsically conducting coating for corrosion protection of structural steels

Among the various corrosion protection strategies for structural steels, coating techniques provide the most cost-effective protection and have been used as the primary mode of corrosion protection. Existing coating techniques however have been used mainly for their barrier capability and therefore all have a limited service life due to oxidation aging, electrolytic degradation, or various inadvertent defects and flaws occurred in and after coating applications. This work investigated the anti-corrosion potential of a π-conjugated polymer-polyaniline (PANi), which was doped into an intrinsically conducting polymer and then included in a two-layer coating system as a primer layer. To achieve a long service life, the primer layer was made by mixing the conductive PANi in a waterborne poly-vinyl butyral solution to provide strong adhesion to steel surface, and then topcoated with a layer of elastomer-modified polyethylene to obtain extra mechanical and barrier protections. Two ASTM standard tests were conducted to evaluate the corrosion durability and tensile adhesion of the two-layer system, in which the system demonstrated superior performance. The Scanning Kelvin Probe Force Microscopy (SKPFM) was used to provide the microscopic evidences for the outstanding performance.

A green MnMgZn phosphate coating for steel pipelines transporting CO2 rich fluids

The transport of CO2 rich fluids via steel pipelines in the CO2 capture and storage (CCS) process requires a strategy for internal corrosion protection in cases where the stream is acidic and hence corrosive due to the formation of carbonic acid. Such protection strategies have been scarcely studied and will need significant research. In this study, one possibility to protect the steel pipelines from internal corrosion during CO2 transport is presented based on treatment of the internal surface with a vanadate-based MnMgZn phosphate coating. The addition of sodium orthovanadate (Na3VO4) in a MnMgZn phosphate bath leads to a significant change in the microstructure of the phosphate coating, which will alter corrosion behaviour significantly. Herein, the effect of vanadate concentration (0.0625, 0.125, 0.25mM) in the phosphate bath is studied with respect to the resultant microstructure and corrosion behaviour of the phosphate coatings. Electrochemical studies such as polarization curves and electrochemical impedance spectroscopy (EIS) were performed in diluted HCl solution at pHs2–4 to investigate the corrosion behaviour and distinguish the dielectric and electric properties of the phosphate coating.

A new corrosion protection coating with polyaniline–TiO 2 composite for steel

Organic coating strategies for corrosion protection with inherently conducting polymers have become important because of restriction on the use of heavy metals and chromates in coatings due to their environmental problems. This work presents the synthesis of polyaniline–TiO 2 composites (PTC) and the corrosion protection behaviour of PTC containing coating on steel. PTC was prepared by chemical oxidation of aniline and TiO 2 by ammonium persulfate in phosphoric acid medium. The PTC was characterized by FTIR, XRD and SEM techniques. Suitable coating with PTC was formed on steel using acrylic resin. Using electrochemical impedance spectroscopy, the PTC containing coating's behaviour in 3% NaCl immersion test and salt spray test has been found out. Results indicate that the coating containing PTC is able to maintain the potential of steel in passive region due to its redox property. The resistance of the coating containing PTC was more than 10 7 Ω cm 2 in 3% NaCl solution after 60 days and 10 9 Ω cm 2 in the salt spray test of 35 days. But the resistance of the TiO 2 containing coating was found to be less than 10 4 Ω cm 2 in both the cases. The high performance of PTC containing coating is attributed to the passivation of steel by polyaniline.

Galvanic coupling between metal substrate and polyaniline acrylic blends: corrosion protection mechanism

Coating strategies for corrosion protection based on intrinsically electronic conducting polymers, become an important research field mainly due to restrictions to the use of heavy metals, which are related to environmental problems. This work presents the corrosion protection behavior of different metals by using coatings based on acrylic blends formed by polyaniline and poly(methyl methacrylate). Raman spectroscopy revealed that the oxidation state of the PANI component of the blend at undamaged films, depends on the metal surface used as substrate. Results indicate that the degree of redox conversion of polyaniline, from emeraldine to leucoemeraldine state, strongly depends on the reducing power of metals showing a galvanic coupling between the substrate and polyaniline. On the other way, results reveal that PANI acts as an anion reservoir, which can release anions in a smart way when damage is produced on the surface of the coating forming a second physical barrier to avoid penetration of aggressive ions. This phenomenon was observed for all metal studied in this work.