What is corrosion in metals?

• A. The deterioration of a metal due to electrochemical or chemical reactions with its environment, resulting in material loss.
• B. A purely mechanical wear process due to friction.
• C. A process of improving metal strength by alloying.
• D. A surface discoloration without material loss.

Answer: (A)

Corrosion is the deterioration of a metal caused by chemical or electrochemical reactions with its surroundings, which leads to loss of metal material. In practice, metals like iron oxidize when exposed to moisture and oxygen, forming oxides that gradually remove metal from the surface. The environment—presence of water, salts, acids, pollutants, and temperature—drives the rate and extent of this process. Sometimes metals form protective oxide layers that slow further attack, but if the environment persists or is aggressive, these layers can break down and continued material loss occurs. This is different from purely mechanical wear, which removes material through physical rubbing or friction, not chemical change, and from a simple surface change in color that doesn’t necessarily involve material loss. Alloying or surface treatments can alter corrosion behavior, but the defining idea remains: corrosion is chemical or electrochemical attack that reduces the metal’s mass.