Corrosion is a galvanic process by which metals deteriorate through oxidation – usually but not always to their oxides. For example, when exposed to air, iron rusts, silver tarnishes, and copper and brass acquire a bluish-green surface called a patina. Of the various metals subject to corrosion, iron is by far the most important commercially. An estimated $100 billion per year is spent in the United States alone to replace iron-containing objects destroyed by corrosion. Consequently, the methods for protecting metal surfaces from corrosion constitute a very active area of industrial research. We also examine the chemical basis for some common methods for preventing corrosion and treating corroded metals.
“Corrosion is a REDOX PROCESS”
While all metals corrode, it is estimated that 25-30% of corrosion could be prevented using suitable protection methods.
How to Prevent Corrosion
We can prevent corrosion by selecting the right
- Metal Type
- Protective Coating
- Environmental Measures
- Sacrificial coatings
- Corrosion Inhibitors
- Design Modification
Different Metal Type
One simple way to prevent corrosion is to use corrosion resistant materials like aluminum or stainless steel. Depending on the application, these metals are used to reduce the need for additional corrosion protection.
The application of a paint coating is a cost-effective way of preventing corrosion. Paint coatings act as a barrier to prevent the transfer of electrochemical charge from the corrosive solution to the metal underneath.
Another possibility is applying a powder coating. In this process, a dry powder is applied to the clean metal surface. The metal is then heated which fuses the powder into a smooth unbroken film. A number of different powder compositions can be used, including acrylic, polyester, epoxy, nylon, and urethane.
Corrosion is caused by chemical reaction between metal & gases in the surrounding environment. By taking the measures to control the environment, these reactions can be minimized to a greater extent. This can simply be reduced to exposure to rain or sea water or by controlling the amounts of sulfur, chlorine or oxygen in the surrounding environment. An example of this would be would be treating the water in water boilers with softeners to adjust hardness, alkalinity, or oxygen content.
Sacrificial coating involves coating the metal with an additional metal type that is more likely to oxidize; hence the term “sacrificial coating.”
There are two main Techniques of Sacrificial Coatings
- Cathodic Protection
- Anodic Protection
Corrosion inhibitors are chemicals that react with the surface of the metal or the surrounding gases to suppress the electrochemical reactions leading to corrosion. They work by being applied to the surface of a metal where they form a protective film. Inhibitors can be applied as a solution or as a protective coating using dispersion techniques.
It helps reduce corrosion & thereby improve the durability of any protective anti corrosive coatings. Ensuring the metal is accessible for regular maintenance will also increase longevity.