Corrosion Inhibitors

Corrosion Inhibitors

The definition of corrosion inhibitor favored by the National Association of Corrosion Engineers (NACE) is “a substance which retards corrosion when added to an environment in small concentrations”.
Corrosion Inhibitor function by one or more of these mechanisms:

1. By adsorption as a thin film on the surface of a corroding material

2. By inducing formation of a thick corrosion product

3. By forming a passive film on the metal surface

4. By changing characteristics of the environment either by producing protective precipitates or by removing or inactivating an aggressive constituent.

If corrosion is viewed as the consequence of an electrochemical cell composed of anode, cathode, electrolyte, and electronic conductor, inhibitors retard corrosion by

1. Increased polarization of the anode

2. Increased polarization of the cathode

3. Increased electrical resistance of the electrolyte circuit resulting from the formation of a deposit on the surface of the metal.

Polarization renders a cathode more anodic and an anode more cathodic.
Inhibitors fall into several classes. The most important corrosion inhibitors are passivating, cathodic, organic, precipitate-inducing, and vapor-phase corrosion inhibitors.