Organic coatings uniform corrosion

Prevention— Uniform corrosion can be prevented or reduced by (1) the proper choice of metal for a given environment (2) the use of metal coatings, such as a paint coating or nonoxidizing organic inhibitors (e.g., benzotriazole or organic amines [160]) in solution that adsorb onto and protect the metal surface or (3) cathodic protection (discussed below). 

Although organically-coated systems are particularly vulnerable to corrosion at defects, such as pinholes, scratches, or cut edges, the truth is that even apparently uniform coatings are prone to corrosion. During exposure of a coating to liquid... 

Although the dry film thickness on the metal edges is somewhat lower, these areas are still efficiently protected against corrosion. The ultrafiltration technique results in a very high transfer effect and a uniform coating paint solids from the bath are deposited on the metal surface without loss. Since electrodeposition paints have a low organic solvent content, air pollution is low. The dip tank contents are not flammable, which reduces insurance costs [11.5]. 

Austenitic stainless steels and hardenable stainless steels such as martensitic, precipitation hardening, and maraging stainless steels are seldom coated, but their corrosion resistance depends on the formation of naturally occurring transparent oxide films. These films may be impaired by surface contaminants such as organic compoimds or metallic or inorganic materials. Treatments are available to clean and degrease the surface of these materials to produce uniform protective oxide films. These usually involve immersion in an aqueous solution of nitric add and a dichromate solution. 

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