COATINGS The total amount of paint sold annually amounts to billions of gallons. In 2000, USA alone manufactured about 3.5 billion gallons of paint. About one-third of the production of paint is used to protect and decorate metal surfaces. All forms of transport, such as trains, ships, automobiles, aeroplanes, underground buried structures, such as tanks, oil and gas pipelines, offshore structures, iron and structures and all metallic equipment require the use of coatings. The coating industry has, therefore, turned out to be one of the largest in terms of production. The importance of coating can be judged from the fact that coating can hardly be ignored in any corrosion protective scheme.

Coatings must have the following characteristics for good corrosion resistance: (a) a high degree of adhesion to the substrate (b) minimum discontinuity in coating (porosity) (c) a high resistance to the flow of electrons (d) a sufficient thickness (the greater the thickness, the more the resistance) (e) a low diffusion rate for ions such as Cl~ and for H20.

7.2 OBJECTIVES The following are the objectives of coatings: (1) Protection of equipment and structures from the environment by acting as a barrier between the substrate and the aggressive environment, such as the marine and industrial environments. (2) Control of solvent losses. (3) Control of marine fouling; certain constituents in coating control the growth of mildew and marine fouling in seawater. (4) Reduction in friction; coating reduces friction between two contacting surfaces. (5) Pleasant appearance; certain types of coatings provide a pleasant appearance and produce attractive surroundings. (6) Change in light intensity; by selection of appropriate coatings the light intensity in rooms and buildings can be varied as desired. (7) Visibility; many combinations of colors because of their visibility from large distances are used on TV and radio towers to warn aircraft. (8) Modification of chemical, mechanical, thermal, electronic and optical properties of materials. (9) Application of thin coatings on low-cost substrates results in increased efficiency and cost savings.