Recent advances and future perspectives for carbon nanostructures reinforced organic coating for anti-corrosion application

Abstract

In this review, the recent advances in the progress of corrosion protective organic coatings containing different kinds of carbon-based nanofillers for the corrosion mitigation of metallic substrates in the chloride solution are summarized. The organic nanocomposite coatings have opened a new field of research for obtaining low-cost coatings with enhanced performance, lifetime, and tailored properties. One of the main advantages of adding carbon nanostructurs to protective organic coatings, is their high barrier performance in corrosion resistance at relatively small amounts of nanofillers. Moreover, these corrosion protective coatings can be utilized in more slender thickness, which lower the expenses. For these reasons, they are considered versatile fillers for polymer matrices. In the following review, the application of the most available carbon-based nanofillers, graphene (G), graphene oxide (GO), carbon nanotube (CNT), and carbon black (CB), carbon nanofiber (CNF), and carbon quantum dot (CQD) in the organic coatings for promotion of corrosion protection performance is investigated. The advantages and disadvantages of fillers introduced for anti-corrosion applications are also discussed, and the best filler is selected from the carbon compounds added.

Introduction

Corrosion is considered as a harmful phenomenon, which threatens the durability of infrastructures and leads to immense costs and damage to industrial units and constructions. Therefore, the total cost and environmental consequences of corrosion problems have become a significant challenge for engineers [1]. Corrosion is a continuous process that cannot be entirely prevented in any corrosive environment. Thus, the corrosion prevention strategies are only concentrated on lowering the kinetics and altering its mechanism. These strategies include alloying steel [2], cathodic and anodic protection [3], the use of protective surface coatings [4], [5], [6], application of corrosion inhibitors [7,8], or combinations of them [9,10]. Using protective coatings is one of the best approaches in order to prevent the metal surfaces from corrosion.

On the other hand, they also delay the access of corrosive species to the substrate, which leads to the progress of the chemical corrosion reactions on the surface. A set of protective coatings, including organic, hybrid organic/inorganic, conversion, and metallic coatings, have been developed as a barrier to prevent or delay the metal damage by limiting the corrosive materials access to the metallic substrate [11]. The conventional anti-corrosive coatings, which have been almost based on heavy metals (such as chromium, phosphate, zinc, and copper-based compounds), are toxic and environmentally harmful [12], [13], [14], [15]. So, there has been an effort to find appropriate non-toxic materials with less negative impacts on the eco-system and high effectiveness in the prevention of the metals from corrosion.

Nowadays, protection of the metal surface against corrosive media by organic coatings is the most conventional and cost-effective method [16]. Organic coatings have considerable physical shielding properties against the penetration of corrosive species, which could significantly delay the reaching time of the corrosive species to the substrate. Furthermore, organic coatings can protect by sacrificial action, or by active corrosion inhibition provided by incorporation of active/passive pigments into the coatings [17]. However, organic coatings are more or less permeable to corrosive species [18]. Free volumes and defects are almost present inside the coating, which could be generated during the coating application or curing processes, leading to the generation of microscopic pathways in the coatings [19]. Therefore, the coatings cannot supply long term corrosion protection. To progress the corrosion protection properties of the organic coatings, various approaches have been proposed. Among the suggested strategies, incorporation of different fillers and anti-corrosive pigments has been detected impressive in the enhancement of corrosion protection. Generally, the anticorrosive pigments can be separated into three categories involving barrier inorganic/organic pigments (e.g., lamellar aluminum pigment [20,21], micaceous iron oxide [22], zinc oxide, and glass flake [23,24], sacrificial metallic pigments (e.g., zinc powder [25]) and inhibitive active pigments (e.g., zinc phosphates [26,27]). In the two past decades, attention has been directed toward the incorporation of nanoparticles into the organic coatings to improve their protection efficiency. It has been shown that nanoparticles such as SiO₂ [28], Al [29], Zn [29], Si [30], ZnO [31], Al₂O₃ [32], TiO₂ [33], ZrO₂ [34], Clay [35], Fe₂O₃ [36], carbon nanotubes (CNTs) [37], graphene (G) and graphene oxide (GO) [38] provide much better barrier properties rather than conventional microparticles owing to their higher surface area/activity and very lower usage content in the coating matrix. Nanoparticles can effectively fill the microscopic porosities and defects existed within the coating and increase the electrolyte pathway length. Among the available nanofillers, the carbon-based nanofillers (Fig. 1) especially CNT and graphene due to their super mechanical strength and high thermal and chemical stability have drawn considerable research interest for exploring the functional nanocomposites with enhanced anticorrosion performance [39]. A review of the literature shows that a number of review articles have covered the covalent/noncovalent functionalization methods of carbon nanostructure. There is a need to present a comprehensive overview on the synthesis, functionalization and application of carbon nanostructure especially on the application of corrosion protection. Herein, an outline of the different types of carbon nanostructure derivatives given with the synthesis methodologies adopted for the preparation of CB, CNT, G and GO. A detailed description provided for the noncovalent and covalent approaches adopted for the synthesis of carbon nanostructure derivatives. The basics of the corrosion protection methods using anti-corrosion coatings and corrosion inhibitors described. The present chapter highlights the application of CB, CNT, G, GO, CNF and CQD its different forms and their functionalized derivatives in corrosion protection namely in the area of anti-corrosion coatings and in corrosion inhibition. In the present review, different methods for the protection of mild steel with oraganic polymer reinforced with CB, CNT, G and GO, the different routes of chemical functionalization of the nanomaterials and their application in anticorrosion coatings and corrosion inhibitors explained. Some drawbacks identified, and the scope of further research in this area has been outlined.