Cathodic polarization conversion coatings

Figure 9. SEM study of the conversion-coated substrate surface after adhesion failure of epoxy-ester coating in cathodic polarization testing. Reproduced from Ref. 29, copyright 1983, American Chemical Society.

The term conversion coating is used to describe coatings in which the substrate metal provides ions which become part of the protective coating. The coating layers are composed of inorganic compounds that are chemically inert. These inert compounds on the surface reduce both anodic and cathodic areas and delay the transit of reactive species to the base metal. This results in increases in the slopes of anodic and cathodic polarization curves, thereby decreasing the rate of corrosion of the substrate. 

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