How is corrosion defined?

• A. Deteriorative loss of a metal as a result of an electrochemical attack
• B. Wear due to friction
• C. Oxidation of polymers
• D. Thermal degradation

Answer: (A)

Corrosion is the deterioration of a metal caused by electrochemical reactions with its environment, leading to material loss. In practical terms, the metal acts as part of an electrochemical cell, with anodic sites where metal atoms dissolve and enter solution, and cathodic sites where reduction reactions (often involving oxygen or water) occur. This electrochemical attack, facilitated by an electrolyte and environmental conditions, erodes the metal and forms corrosion products such as oxides or hydroxides. This concept is distinct from wear due to friction (mechanical removal), oxidation of polymers (not metals), or thermal degradation (breakdown due to heat). An iron surface rusts when exposed to water and oxygen because of these electrochemical processes, illustrating corrosion as electrochemical deterioration of a metal.