Question

Consider the following statements with respect to corrosion :

1. It is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide.

2. It is accelerated by warm temperatures and by acids and salts.

3. Galvanizing can protect against corrosion of iron and steel.

Which of the statements given above are correct?

1. 1 and 2 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3 

Answer 1

Correct Answer - Option 4 : 1, 2 and 3 

The correct answer is 1, 2 and 3.

• Corrosion - 
  • Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide.
    • Hence, statement 1 is correct.
  • It occurs whenever a gas or liquid chemically attacks an exposed surface, often a metal, and is accelerated by warm temperatures and by acids and salts. 
    • Hence, statement 2 is correct.
  • Normally, corrosion products (e.g., rust, patina) stay on the surface and protect it.
  • Removing these deposits reexposes the surface, and corrosion continues.
  • Some materials resist corrosion naturally; others can be treated to protect them (e.g., by coating, painting, galvanizing, or anodizing).

• Galvanizing - 
  • Galvanizing, protection of iron or steel against exposure to the atmosphere and consequent rusting by application of a zinc coating. 
    • Hence, statement 3 is correct.
  • Properly applied, galvanizing may protect from atmospheric corrosion for 15 to 30 years or more.
  • As discontinuities or porosity develop in the coating, galvanic or electrolytic action ensues; the iron or steel, however, is protected by sacrificial corrosion, a phenomenon in which, as long as the zinc and the iron are in contact, atmospheric oxidation spares the iron and affects the zinc.
• Anodizing - 
  • It is a method of plating metal for such purposes as corrosion resistance, electrical insulation, thermal control, abrasion resistance, sealing, improving paint adhesion, and decorative finishing.
  • Anodizing consists of electrically depositing an oxide film from an aqueous solution onto the surface of a metal, often aluminum, which serves as the anode in an electrolytic cell.