ABSTRACT
Organic coatings have been the most common and cost-effective means to protect corrodible metallic structures and objects [1, 2]. The use of organic coatings in corrosion protection includes pretreatment of metals and application of primers. Since most corrosion reactions of metals are of electrochemical nature, the currently adopted approach in design and development of corrosion control coatings
depends on electrochemical passivation of metal surfaces. In other words, corrosion control or corrosion protection of metallic materials has been relying on the corrosion inhibitors incorporated in metal pretreatment and primer coatings. Unfortunately, most of the more efficient corrosion inhibitors, which are usually heavy metal-containing compounds, are toxic and cause serious health and environmental problems. For example, the widely used chromates (6+ valence chromium) in both metal pretreatment and primer formulation are well-known carcinogenic materials [3]. Moreover, the wet chemistry in metal pretreatment such as alkaline cleaning or acid pickling produces huge amount of liquid wastes, which need tremendous post-treatment steps and are very costly to prevent pollution to the environment. The traditional solvent-borne primers also release huge amounts of volatile organic compounds (VOCs) into the air during their applications. New environmental regulations severely limit the use of these hazardous metal pretreatments and these solvent-borne primers, making their continuous use in either the metal pretreatment or in the coating pigmentation very difficult and soon will be impossible [4, 5]. Nowadays, therefore, design and development of chromate-free and solvent-free pretreatment methods and primer coatings have been the main goals of the corrosion scientists and researchers in both universities and coating industries.
