Advanced Anticorrosive Coatings Prepared from Polymer-Clay Nanocomposite Materials

Abstract

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.