Corrosion
Definition and meaning of Corrosion in chemistry.
Corrosion is the gradual degradation of a metal caused by chemical or electrochemical reaction with its environment, in which the metal is oxidized and converted into a more thermodynamically stable compound such as an oxide, hydroxide, or sulfide.
In more detail
Corrosion usually proceeds through an electrochemical mechanism on the metal surface: at anodic sites the metal loses electrons and dissolves (M → Mⁿ⁺ + ne⁻), while at cathodic sites a reduction occurs, most often O2 + 2H2O + 4e⁻ → 4OH⁻. The metal acts as the electron conductor and the surrounding moisture or electrolyte completes the circuit, so factors like dissolved salts, low pH, and contact between dissimilar metals (galvanic corrosion) speed the process. Because corrosion is thermodynamically favorable for most metals (returning them toward the stable, low-energy state found in ores), it can only be slowed, not eliminated, through barriers, alloying, or electrochemical protection.
Key facts
| Field | Physical Chemistry |
|---|---|
| Classic example | Rust, Fe2O3·xH2O |
| Mechanism | Electrochemical oxidation-reduction |
| Common prevention | Galvanizing, cathodic protection, alloying (e.g., stainless steel) |
The rusting of iron: 4Fe(s) + 3O2(g) + 2xH2O(l) → 2Fe2O3·xH2O(s), where iron is oxidized at anodic regions and dissolved oxygen is reduced at cathodic regions of the same surface.
Frequently asked questions
Is corrosion the same thing as rusting?
No. Rusting refers specifically to the corrosion of iron and steel, producing hydrated iron(III) oxide; corrosion is the broader term for the degradation of any metal by its environment.
Why does salt water make corrosion worse?
Dissolved ions increase the conductivity of the surface electrolyte, allowing electrons and ions to move more easily between the anodic and cathodic sites, which speeds up the redox reactions.