Rusting and its prevention

Rusting is a chemical process that affects iron and steel, causing them to corrode and weaken over time. Preventing rust is essential for preserving the structural integrity of materials and reducing maintenance costs.

Conditions for rusting

Rusting occurs when iron or steel is exposed to both:

• 1. Oxygen (from air)

  2. Water (e.g., moisture or rain)

  3. Chemical Reaction: Iron reacts with oxygen and water to form hydrated iron(III) oxide, also known as rust.

Equation: 

Iron + Oxygen + Water → Hydrated iron(III) oxide

4Fe(s) + 3O2(g) + 6H2O(l) → 4Fe(OH)3(s)

Rusting is prevented when air is excluded (left) or water is excluded (middle) but occurs in the presence of air and water (right)

Barrier methods

Barrier methods work by excluding oxygen and water from coming into contact with the metal. These include:

• Painting: Used on structures such as bridges and vehicles. Brightly colored paint on ships prevents rust and enhances visibility.

• Greasing: Common for moving parts like bike chains and machinery.

• Plastic Coating: Applied to objects like garden tools or wire mesh to provide a durable, waterproof layer.

The coating must remain intact. Any damage (e.g., scratches in paint) can allow rust to form underneath.

Sacrificial protection