Environmental change is often brought about by the use of inhibitors, which may, depending upon their chemical composition, influence either or both the rate of the anodic and cathodic reactions. Alternatively, an inhibitor may form a relatively thick film on the surface and thereby increase the electrolyte resistance of the circuit. Figure 11.21 presents schematic polarization curves illustrating how anodic, cathodic, and mixed inhibitors influence the rate of corrosion [50]. Classification of inhibitor systems is often based upon the following [50, 51]:

• Anodic or cathodic inhibitors—depending upon which electrode reaction is affected.

• Oxidizing or nonoxidizing inhibitors—depending upon the ability to pas-sivate the metal. In the case of the latter, dissolved oxygen in the aqueous phase is required to form the passive film.

• Organic or inorganic inhibitors—depending upon the chemical nature of the inhibitor.

Examples of the application of different types of inhibitor are given in Table 11.6.

anodic o 0-

anodic o 0.

cathodic cathodic

Log i Log i

• Corrosion rate without inhibitor

♦ Corrosion rate with inhibitor mixed o

0 0

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