Prevention of corrosion protective oxide layers

The enormous cost of corrosion of iron to society has prompted many efforts to devise ways of reducing or preventing it. Several electrochemical or chemical methods are available. One method is removal of the cathodic species (usually oxygen). Most methods are based on the principle of providing a barrier between the reacting species. The barrier may be physical, i. e. a metal or paint coating or a protective oxide film, or electronic, i. e. making the iron thermodynamically immune. Here, the em- 

Cathodic inhibitors promote coverage of iron by a protective coating, but this need not be an iron oxide. Immersion of iron in a solution of phosphoric acid containing a suitable catalyst causes precipitation of a mixed Fe -Fe phosphate film which serves as a base for a coating of paint. 

Anticorrosive paints containing pigments with either chemical or electrochemical action may induce formation of protective coatings at the metal-paint interlayer (Etz-rodt, 1993). These protective coating may be metal-substituted iron oxides iron phosphate precipitates or even a green rust - Fe Fe 0HigC03 4H2O (Chemical Week, 1988). 

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