Increasing the anodic or cathodic polarization behavior (Tafel slopes);
Reducing the movement or diffusion of ions to the metallic surface;
Increasing the electrical resistance of the metallic surface.
Classification of inhibitors
Inhibitors are chemicals that react with a metallic surface, or the environment this surface is exposed to, giving the surface a certain level of protection. Inhibitors often work by adsorbing themselves on the metallic surface, protecting the metallic surface by forming a film. Inhibitors are normally distributed from a solution or dispersion. Some are included in a protective coating formulation. Inhibitors slow corrosion processes by either:
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Increasing the anodic or cathodic polarization behavior (Tafel slopes); |
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Reducing the movement or diffusion of ions to the metallic surface; |
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Increasing the electrical resistance of the metallic surface. |
The scientific and technical corrosion literature has descriptions and lists of numerous chemical compounds that exhibit inhibitive properties. Of these, only very few are actually used in practice. This is partly due to the fact that the desirable properties of an inhibitor usually extend beyond those simply related to metal protection. Considerations of cost, toxicity, availability and environmental friendliness are of considerable importance.
Inhibitors have been classified differently by various authors. Some authors, for example, prefer to group inhibitors by their chemical functionality. However, by far the most popular organization scheme consists in regrouping corrosion inhibitors in a functionality scheme as follows:
| Passivating inhibitors |
| Cathodic inhibitors |
| Organic inhibitors |
| Precipitation inhibitors |
| Volatile corrosion Inhibitors |
