Recent development in polymer coating to prevent corrosion in metals: A review

Self-healing coatings offer tremendous application prospects in the field of preventing metal corrosion because of their superior functionality. The coordination of barrier performance and self-healing ability, however, continues to be difficult. Herein, a polymer coating based on polyethyleneimine (PEI) and polyacrylic acid (PAA) with self-repairing and barrier ability was designed. Introducing the catechol group into the anti-corrosion coating increases the adhesion and self-healing efficiency of the coating, providing a guarantee for the long-term stable bonding between the anti-corrosion coating and the metal substrate. Small molecular weight PAA polymers are added to polymer coatings to increase their self-healing capabilities and corrosion resistance. Because layer-by-layer assembly creates reversible hydrogen bonds and electrostatic bonds that help the coating repair itself when it is damaged, and because the traction of small molecular weight polyacrylic acid speeds up this process. When polyacrylic acid (PAA) with a molecular weight of 2000 was present in the coating at a concentration of 1.5 mg/mL, the coating's self-healing capability and corrosion resistance were at their peak. The PEI-C/PAA45W -PAA2000 coating completed the self-healing within 10 min, and the corrosion resistance efficiency (Pe ) was as high as 90.1 %. The polarization resistance (Rp ) was maintained at 7.67×104 Ω cm2 after immersion for more than 240 h. It was better than other samples in this work. The polymer provides a new idea for the prevention of metal corrosion.

The degradation of a material due to interaction with its surroundings is known as corrosion and it is an international issue. The most widely used methods of reducing corrosion are coatings and corrosion inhibitors. Coatings or corrosion inhibitors provide a layer over the metallic substrate that prevents corrosion. Naturally occurring and manufactured polymers have been evaluated for their efficacy in protecting against metal corrosion as alternatives to hazardous inorganic and organic corrosion inhibitors. Corrosion prevention by these compounds is mainly ascribed to their adsorption at the metal/solution contact. The precise effect of an inhibitor is contingent upon its contact with the metal surface, which alters either the mechanism of the electrochemical corrosion process or the surface area accessible for the process. The corrosion inhibition qualities of polymers are covered in depth in this chapter.

Corrosion control is an important subject of increasing interest to the modern metallic finishing industry. Surface modification of metallic substrates by organic or polymeric coatings is an essential approach for enhancing surface properties such as wear, oxidation, and corrosion. Various conventional techniques are utilized to depositing the desired materials onto the metallic substrate to achieve surface modifications with better protection for the substrate. Organic or polymeric coatings on metallic substrates provide an effective barrier between the metal and its environment and/or inhibit corrosion through the presence of chemicals. Chromium-containing compounds (CC) have generally been used as effective anticorrosive coatings in the past decades. However, due to the environmental and health concerns, CCs may need to be replaced by alternative materials that would not pose biological and ecological hazards. Thus, research has focused on the development of novel polymeric coating materials that contain effective anticorrosive agents. During the early stage of corrosion protection engineering, various neat organic or polymeric coatings were developed. These coatings generally function as a physical barrier against aggressive species such as O2 and H+ that cause decomposition. Examples of representative polymers are include epoxy resins [MacQueen & Granata, 1996; Dang et al., 2002], polyurethanes [Moijca et al., 2001], and polyesters [Malshe & Sangaj, 2006; Deflorian et al., 1996]. Moreover, conjugated polymers such as polyaniline [Wessling & Posdorfer, 1999; Tan & Blackwood, 2003], polypyrrole [Iroh & Su, 2000, Krstajic et al., 1997], and polythiophene [Kousik et al., 2001], have also been employed as advanced anticorrosive coatings due to their redox catalytic properties, forming metal oxide passivation layers on metallic substrates. Conversely, not all neat polymeric coatings are permanently impenetrable because small defects in the coatings can lead to gateways that allow corrosive species to attack the metallic substrate; thus, localized corrosion can occur. As a second line of defense against corrosion, various nanoscale inorganic additives have been incorporated into various polymer matrices to generate a series of organic–inorganic hybrid anticorrosive coatings. Recently, montmorrillonite (MMT)–layered silicate (clay) has attracted intensive research interest for the preparation of polymer–clay nanocomposites (PCNs) because its lamellar elements display high in–plane strength, stiffness, and high aspect ratios. Typically, the chemical structures of MMT consist of two fused silica tetrahedral sheets that sandwich an

The successful use of polymeric coatings for corrosion prevention or mitigation is often hindered by their inherently porous microstructure that fails to resist the ingress of detrimental species and/or by their vulnerability to damage by surface abrasion, wear, or scratches. Incorporation of nanomaterials in polymeric coatings can greatly improve their barrier performance. While the last decade has seen a substantial amount of research on polymeric nanocomposite coatings, the knowledge underlying the critical roles nanomaterials play remains scattered. This chapter discusses the utilization of nanotechnology to greatly enhance the properties of polymer-based coatings for anticorrosion applications, by modifying the microstructure of the coating bulk or endowing it with additional functionality. It starts with a brief discussion of the relevant knowledge base, including: microstructure of polymer nanocomposites, influence of nanomodification on properties of polymeric coatings, fabrication approaches, and the use of polymeric nanocoating as a carrier for corrosion inhibitors. It also provides a review of technological advances in the use of nanotechnology to produce high-performance polymeric coatings with outstanding corrosion resistance and other relevant properties. The chapter concludes with a snapshot review of the advanced characterization of nanocomposite coatings for corrosion protection.

In recent years, we have been developing a holistic approach towards the design and screening of novel corrosion inhibitors for solution and coating applications. One of the main challenges in identifying and designing new inhibitors is being able to evaluate different materials under similar conditions to determine their potential efficiency to prevent corrosion. This is further complicated by the need to replicate the environmental conditions where the corrosion inhibitors will be used, understanding the complex chemical interactions in the bulk electrolyte, at the metal interface and in polymer coatings, the large number of different evaluation tests that need to be undertaken and the large amounts of chemicals, metal substrates, instrument techniques, and labour cost that are required to develop commercially viable corrosion inhibitors. To minimise some of these challenges so that we can identify superior corrosion inhibitors worthy of further detailed investigation and development, we are developing computational methods to model inhibitor materials, high-throughput (HTP) corrosion optical solution assay, HTP electrochemistry assay, thin film characterisation methods, neutral salt spray, and novel coating assay protocols. In an effort to accelerate these time consuming processes, we have started to integrate some of these assays into our FASTER™ robotic system. This presentation will highlight some of these challenges and how we have developed some robust HTP assays to expedite our corrosion inhibitor materials development program for solution and coating systems.

In recent years, we have been developing a holistic approach towards the design and screening of novel corrosion inhibitors for solution and coating applications. One of the main challenges in identifying and designing new inhibitors is being able to evaluate different materials under similar conditions to determine their potential efficiency to prevent corrosion. This is further complicated by the need to replicate the environmental conditions where the corrosion inhibitors will be used, understanding the complex chemical interactions in the bulk electrolyte, at the metal interface and in polymer coatings, the large number of different evaluation tests that need to be undertaken and the large amounts of chemicals, metal substrates, instrument techniques, and labour cost that are required to develop commercially viable corrosion inhibitors. To minimise some of these challenges so that we can identify superior corrosion inhibitors worthy of further detailed investigation and development, we are developing computational methods to model inhibitor materials, high-throughput (HTP) corrosion optical solution assay, HTP electrochemistry assay, thin film characterisation methods, neutral salt spray, and novel coating assay protocols. In an effort to accelerate these time consuming processes, we have started to integrate some of these assays into our FASTER™ robotic system. This presentation will highlight some of these challenges and how we have developed some robust HTP assays to expedite our corrosion inhibitor materials development program for solution and coating systems.

Electrochemical impedance spectroscopy response of water uptake in organic coatings by finite element methods

Chapter 24 - Corrosion resistant nanoscale polymer-based coatings

Many systems benefit from the ability to autonomously signal the occurrence of damage. The development of smart polymer coatings on metals can address scientific challenges such as nondestructive detection of early corrosion to avoid further destruction of materials. Here, pH‐responsive polymer coatings on metals such as steel, aluminum, magnesium, and copper alloys are reported. The defect areas of coatings can gradually exhibit strong fluorescence as the corrosion starts. Based on the fundamental understanding of electrochemical mechanisms in metal corrosion, the designed pH‐responsive polymer coating is dormant before crack occurrence. However, the on‐demand release of fluorescent molecules from nanocontainers in coatings occurs as corrosion proceeds with increasing pH value by transformation into highly active fluorescence indication from the dormant state at the stage of corrosion commencement. The developed smart polymer coatings can report the corrosion caused by a coating failure which provides a new strategy for nondestructive corrosion detection. image

Metal degradation due to corrosion is a major challenge in most industries, and its control and prevention has to maintain a balance between efficiency and cost-effectiveness. The rising concern over environmental damage has greatly influenced this domain, as corrosion prevention should comply with the waste regulations of different regions. In this respect, a fundamental question is which modern synthetic materials are more viable from the point of view of their effectiveness. Therefore, this paper is aims to provide an advanced and holistic review of corrosion prevention and control methods. Corrosion prevention techniques have become extensive; however, the literature indicates that polymer coatings, nano-composite coatings, and encapsulation techniques consistently provide the most efficient and feasible outcomes. Therefore, this review article examined the phenomenon of corrosion inhibition mainly from the perspective of these three techniques. Moreover, this research utilized secondary qualitative methods to obtain data and information on comparative techniques. It is found that due to the rapid development of novel materials, corrosion inhibition techniques need to be developed on scales that are more general, so that they could be applied to varying environments. The self-healing coatings are generally based on epoxy-resins incorporated with synthetic compounds such as inhibitor ions, amino-acids, or carboxylic acids. These coatings have become more widespread, especially due to bans on several traditional prevention materials such as compounds of chromium (VI). However, self-healing coatings are comparatively more costly than other techniques because of their method of synthesis and long-term durability. Therefore, although self-healing nanomaterial-based coatings are viable options for limited usage, their utilization in large and complex facilities is limited due to the costs involved. Amino acids and other biological macro-molecules provide another option to attain environmental sustainability and long durability, especially due to their origins being most of naturally occurring compounds such as lignin, cellulose, and proteins.

Smart coating based on polyaniline acrylic blend for corrosion protection of different metals

Chromate free corrosion inhibitors are searched for to mitigate the economic loss caused by mid-steel corrosion. Here, we show metal-free organic inhibitors having free coumarate anions that can be used either as direct corrosion inhibitors or incorporated into a polymer coating obtained by UV-curing. Four different ionic liquid monomers and polymer coatings with hexoxycoumarate anion and different polymerizable counter cations were investigated. Potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analyses have verified their corrosion inhibition performance on a mild steel AS1020 surface. In the case of the coumarate ionic liquid monomers, the most promising inhibitor is the one coupled with the ammonium cation, showing an inhibition efficiency of 99.1% in solution followed by the imidazolium, pyridinium, and anilinium. Next, the ionic liquid monomers were covalently integrated into an acrylic polymer coating by UV-photopolymerization. In this case, the barrier effect of the polymer coating is combined with the corrosion inhibitor effect of the pendant coumarate anion. Here, the best polymer coatings are those containing 20% imidazolium and pyridinium cations, presenting a greater impedance in the EIS (Electrochemical Impedance Spectroscopy) measurements and less evidence of corrosion in the scribe tests. This article shows that the cationic moiety of coumarate based ionic liquids and poly(ionic liquid)s has a significant effect on their excellent corrosion inhibition properties for a mild steel surface exposed to aqueous chloride solutions.

Corrosion fatigue is an area of concern for the United States Air Force (USAF) and other Department of Defense (DoD) organizations. Often DoD corrosion prevention systems include chromate containing coatings, typically in the form of chromate conversion coatings and polymer primers. Chromate has been used successfully for many years within the DoD to prevent corrosion damage. However the environmental and personnel risks associated with chromate coatings have caused the USAF to pursue non-chromate containing corrosion prevention coatings [1]. To fully quantify chromate replacement coatings, an understanding of the effects that chromate has on corrosion fatigue crack growth rates must be fully characterized. Some researchers have shown that high levels of chromate added to 0.6 M NaCl full immersion corrosion fatigue tests on 7xxx series aluminum alloys slow the fatigue crack growth rate substantially [2,3]. The limitation of that research was that the amount of chromate present in the test solution environment was not connected to expected leach rates of chromate from polymeric coatings and a high solubility salt was used. The majority of DoD assets are protected from corrosion by polymer coatings loaded with corrosion inhibitors. For these coatings to slow fatigue crack propagation the corrosion inhibitors must become mobile as a consequence of hydration of the polymer coating matrix. Based on this mechanism of corrosion inhibitor release, the examination of atmospheric corrosion fatigue becomes important to help understand how inhibitors work in real world situations with hydrated salt layers rather than only fully immersed solutions.

Corrosion in metals and its alloys is an inevitable phenomenon but can be controlled by suitable classical methods like process control, cathode protection, surface treating methods, impurity reduction in metals and addition of metals to form alloys. Nevertheless, the employment of corrosion inhibitors is still a noteworthy and simplest of all the above processes in protecting the metals and alloys especially in acidic media. Protection of metals against corrosion not only prevents corrosion but also is beneficial in terms of money loss as far as industrial equipment, surfaces and vessels are concerned. Since the use of organic and inorganic inhibitors are highly discouraged due to their high cost and toxicity, necessity has adequately aroused the development of corrosion inhibitors which are natural and green. Trends, nowadays, focussed in controlling corrosion in various metals and alloys through green corrosion inhibitors consisting of natural elements alone. In contrast to the inorganic inhibitors, green corrosion inhibitors are characterized by biodegradability, low cost and meagre toxicity. Several researchers are now turning themselves towards the research of green inhibitors which are of no threat to humans and the ecosystem. The current discussion is focussed on the fundamentals of corrosion, corrosion inhibition, materials used for it and case studies of green inhibitors used for corrosion control in various conventional and monolithic metals.

Chapter 24 - Ionic liquids as green corrosion inhibitor