ANODIC POLARIZATION

Anodic surfaces can be polarized by formation of a thin, impervious oxide layer. This film formation is accomplished by a mechanism known as chemisorption and is attributed to lower valence bonding at metal sites. Stainless steel naturally forms such films.

With most metals, however, the film formation must be aided by the addition of such anodic corrosion inhibitors as chromate, nitrite, etc. These and other anodic corrosion inhibitors will be discussed in more detail later in this section.

PASSIVITY

When corrosion reactions are completely polarized, the metal is said to be in a "passive state". At this point, there is no difference in potential between the anode and cathode areas, and corrosion ceases. When polarization is disrupted in a passive metal at a given point, a very active anodic site is set up, with resultant accelerated local corrosion, particularly if the metal was strongly anodically polarized.