Corrosion is an electrochemical process where metals gradually deteriorate due to reactions with their environment. In simple terms, it’s like a spontaneous battery reaction happening on the metal’s surface.
Here’s how it works:
1. Electrochemical Nature of Corrosion
- Anodic reaction (oxidation): Metal atoms lose electrons and form metal ions.
- Example: Fe → Fe²⁺ + 2e⁻
- Cathodic reaction (reduction): Electrons released by the metal reduce oxygen or hydrogen ions from water or air.
- Example: O₂ + 4e⁻ + 2H₂O → 4OH⁻
2. Electrolyte Role
- Water, especially with salts, acts as an electrolyte, allowing ions to move and complete the electrical circuit.
3. Corrosion Cells
- Corrosion happens at microscopic sites, forming tiny galvanic cells:
- One part of the metal acts as anode (where metal corrodes).
- Another part acts as cathode (where reduction happens).
4. Examples
- Rusting of iron: Iron reacts with oxygen and water to form Fe₂O₃·xH₂O (rust).
- Tarnishing of silver: Silver reacts with sulfur compounds to form silver sulfide.
In short: Corrosion is an electrochemical reaction where metal loses electrons (oxidizes) and reacts with its environment, often forming rust or other compounds.