Corrosion and rust preventive coatings cover the surface of a part and protect the underlying surface from rusting, oxidation, tarnishing, or other types of corrosion. The coating acts as a protective layer that adheres to the underlying surface. They may contain inhibitors that repel corrosive species or they may include chemicals that react with the surface improving its physical properties.

All metals with exception of gold and platinum are susceptible to corrosion. In the presence of an oxidizing environment metallic surfaces react with corrosive species forming compounds such as oxides, hydroxides, and sulfides.

 
Types of Corrosion and Rust Preventive Coatings

Corrosion and rust preventive coatings include hard coatings, passivates, and conversion coatings. 
 
Hard coatings are wear resistant coatings whose hardness is typically greater than most materials other than diamonds. They are designed to cover and protect underlying surfaces that are to be exposed to extreme environments and demanding applications. They are typically composed of ceramics or metal carbides. They provide outstanding wear resistance and are inherently corrosion resistant.

Passivates are applied to and react with material surfaces (substrates) in order to remove corrosion-causing impurities and to form a thin protective layer. The passivation layer inherently resists corrosion from certain substances that more readily corrode the substrate. More detailed information can be found on the Engineering360 Passivates Selection Guide.

Conversion coatings react with material surfaces (substrates) in order to form a complex surface film. A chromate conversion coating on aluminum is a type of conversion coating which produces a complex, non-crystalline, non-porous oxide film entrapped with chromates and dichromates.

Standards

Standards related to corrosion and rust preventive coatings can be found at the Engineering360 Standards Library. Some example standards include:

• ASTM MNL20—Corrosion tests and standards: application and interpretation
• ISO Handbook on Corrosion

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