Prevention of Corrosion

Corrosion results in loss of materials and money. It must be minimized or controlled.

To avoid corrosion

• Use noble metals
• Use purest possible metal - not possible in real life
• Use corrosion resistant alloys
• Use non-metals (like polymers or ceramics)

Cathodic protection

Corrosion can be prevented by making the metallic structure as cathode.

2 types of cathodic protection is available.

Galvanic protection

Metal to be protected is made cathode by connecting it to an anodic metal (which is called the sacrificial anode). and are commonly used as anodic metals. Aka. sacrificial anodic protection.

Uses

• Protection from soil corrosion of buried pipelines, underground cables
• Protection from marine corrosion of cables, ship hulls, piers
• Prevention of rust in water boilers by inserting
• Minimizing engine corrosion using

Impressed current cathodic protection

Suppressing corrosion by supplying external current (opposite to corrosion). The applied current converts corroding metal from anode to cathode.

Usually current is derived from DC sources with an inert anode.

Modifying the environment

Corrosion can be prevented by adding inhibitors to the environment.

Examples:

• Hydrogen evolution poisons - used when cathodic reactions are HER.
• Oxygen scavengers - eliminates oxygen from the corroding medium. used when cathodic reactions are ORR.

Protective coatings

Preventing corrosion by covering the surface by means of protective coatings.

The coating acts as a physical barrier between the coated metal surface and the environment.

2 types:

• Inorganic
  • Metallic
  • Non-metallic
• Organic
  • Paints

Note

Stainless steel is usually protected from corrosion by layer.

Galvanizing

The process of coating steel sheets with a thin coat of to prevent them from rusting.

The process steps are, Steel article is:

1. cleaned with diluted
2. washed with distilled water
3. dried
4. dipped in a bath of molten

And now the coating will have been applied.

Paints

Paint is a viscous, opaque mechanical dispersion mixture of one or more pigments (dye) in a vehicle (drying oil).

Corrosion inhabitors are added to paints.

Note

Coating is enough to prevent corrosion. But in steel, coating is preferred instead of coating. The reason for this is, when coating is used, when the coating is damaged (even a little), the corrosion of steel will not be prevented. When is used, it will work as an anode and steel will be protected from corrosion.