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COATINGS ARE IMPORTANT WIDELY USED PRODUCTS that provide corrosion protection of metals and other substrates. Paints that contain anti-corrosion pigments account for about 65 %–70 % of all areas protected by anti-corrosion coatings. Paint provides a number of desirable attributes including relatively low cost, simplicity of application to simple and complex structures, aesthetic beauty, ease of repair and restoration, as well as metal corrosion protection that is markedly enhanced when anti-corrosion pigments are present. Coatings may be classified in various ways such as by their end use, surface character, and so on. For example, an end-use classification might include coatings for transportation vehicles and associated hardware, such as boats, ships, piers, and other items subject to marine environments, such as reactors, drums, piping, buildings, etc., exposed to harsh industrial environments; pipeline coatings, architectural coatings; artists' paints that have aesthetic, aging, substrate nature needs; and many others. Each of these classes has different requirements. Marine coatings must be resistant to high humidity, chloride presence, and aqueous immersion; pipeline coatings must be resistant to crude oil, natural gas, water and aggressive aqueous solutions, and solvents; and so on [1–5]. Each end use will have its own particular requirements. Various chapters in this manual deal with coatings for a variety of end uses. The three main components of an organic paint are pigment, binder, and volatile vehicle. The pigment is an insoluble, finely ground material that provides color and opacity as well as corrosion resistance and water barrier properties when particular pigments are used. The binder is the polymeric, nonvolatile portion of a formulated coating. It is the important ingredient that forms a film as paint dries, and it holds the pigment particles or other additives in a separated, suspended state within the paint film. Binders are either polymeric in nature or are capable of reacting and forming a thermoplastic or thermoset polymeric film under specified conditions. They are comprised of oils, epoxides, alkyds, polyesters, acrylics, vinyls, and the like. The volatile vehicle dissolves or disperses the binder, and it allows the coating to form in a thin, continuous film. In certain formulations, a curing agent or hardener will be incorporated into the system. In the case of ultraviolet-radiation curable coatings, the curing agent will be a photoinitiator that effects rapid polymerization of combinations of monomeric and oligomeric species.
Research Professor, Center for Investigation and Advanced Study (CINVESTAV), Yucatan