E

aR = reasonably effective, E = effective, V = variable effectiveness, PE = partially effective.

aR = reasonably effective, E = effective, V = variable effectiveness, PE = partially effective.

The concentration of the inhibitor will be dependent upon the metal being protected and the nature of the environment. A certain minimum concentration is required for an inhibitor to be fully effective. In fact inhibitors may be classed as safe or dangerous, for example, an insufficient concentration of a safe inhibitor can lead, at worst, to a rate equal to that of an uninhibited system. Conversely an insufficient concentration of a dangerous inhibitor can lead to accelerated localized attack that is, pitting. Anodic inhibitors are often classed as dangerous inhibitors because they rely on complete passivation of the metal surface for effective corrosion control.

Inhibitors may also be used in the absence of a water phase. These types of inhibitor are known as vapor-phase inhibitors (VPI) and are used mainly in closed systems and packaging. As their name suggests, they rely upon volatilization of a compound into the atmosphere around the product to be protected, the inhibitor then being absorbed onto the surface of the metal. Typical examples include cyclohexylamine nitrate, sodium benzoate, and dicyclohexylamine carbonates.

0 0

Post a comment