Cathodic inhibitors oxygen scavengers

A typical good corrosion inhibitor will give 95% inhibition at concentration of 80ppm, and 90% at 40ppm. Some of the mechanism of its effect are formation of a passivation layer (a thin film on the surface of the material that stops access of the corrosive substance to the metal), inhibiting either the oxidation or reduction part of the redox corrosion system (anodic and cathodic inhibitors), or scavenging the dissolved oxygen. 

Formulations usually contain a combination of different anodic and cathodic inhibitors. Commonly used are ortho- and polyphosphates, phosphonates, tannins, lignins, benzoates, silicates, chromates, molybdates, nitrites, nitrates, zinc salts, aromatic azoles, carboxylic acids, amides, amines, soluble oils, and oxygen scavengers, such as hydrazine and sulfites [3, 46]. Some of these substances (e.g. silicates) are employed predominantly in synergy with other inhibitors, whereas in other cases the combination of inhibitors may have adverse effects (e.g. nitrites and organic amines or amides may form carcinogenic nitrosamines at elevated temperatures). 

Cathodic inhibitors either slow the cathodic reaction itself or they selectively precipitate on cathodic areas to increase circuit resistance and restrict diffusion of reducible species to the cathodes. Acid inhibitors such as arsenic and antimony compounds and also oxygen scavengers are examples of cathodic inhibitors (Tumipseed 1997). 

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