Briefly explain wet corrosion. How Corrosion can be prevented by Metallic coating and using corrosion inhibitors?

  

What is Corrosion? 

It is basically defined as a natural process that causes the transformation of pure metals into undesirable substances when they react with substances like water or air. 

This reaction causes damage and disintegration of the metal, starting from the portion of the metal exposed to the environment and spreading to the entire bulk of the metal.

Factors Affecting Corrosion

1. Exposure of the metals to air containing gases like CO2, SO2, SO3 etc.

2. Exposure of metals to moisture, especially salt water (which increases the rate of corrosion).

3. Presence of impurities like salt (For example, NaCl).

4. Temperature: An increase in temperature increases corrosion.

5. Nature of the first layer of oxide formed: Some oxides like Al2O3 form an insoluble protecting layer that can prevent further corrosion. Others, like rust, easily crumble and expose the rest of the metal.

6. Presence of acid in the atmosphere: Acids can easily accelerate the process of corrosion.

Metallic Coating and Corrosion Inhibitors are 

effective methods to prevent corrosion:

Metallic Coating:

Barrier Protection: Coatings like paint or galvanization create a physical barrier that prevents corrosive substances from reaching the metal surface.

Sacrificial Coating: Metals like zinc can be used to coat steel. Zinc corrodes preferentially, protecting the underlying steel (a process known as cathodic protection).

Corrosion Inhibitors:

Chemical Inhibitors: These substances are added to the environment to reduce the rate of corrosion. They can form a protective film on the metal surface or react with corrosive agents to neutralize them.

Types: Common inhibitors include silicates, phosphates, and organic compounds.