On the surface of a single metal, anodic and cathodic regions formed by inclusions, strain, oxygen concentration differences and the like, through which corrosion proceeds as in a battery.
Japanese name: 局部電池
Local cell appears in 1 practice question across 1 topic, including Corrosion and surface treatment.
Answer: B. O₂ + 2H₂O + 4e⁻ → 4OH⁻
Even on the surface of a single metal, inclusions, grain boundaries, strain and nonuniformities in the environment create regions of lower and higher potential, and with the metal itself acting as the wire, many small cells form. These are local cells. At the lower-potential anodes, iron dissolves as Fe → Fe²⁺ + 2e⁻ (the choice giving this equation is the anode reaction), and at the cathodes that accept these electrons, in neutral water, the main reaction is reduction of dissolved oxygen, O₂ + 2H₂O + 4e⁻ → 4OH⁻. The Fe²⁺ and OH⁻ produced react and are further oxidized into red rust (FeOOH and others). Hydrogen evolution, 2H⁺ + 2e⁻ → H₂, is the main reaction in acidic solutions rich in H⁺; in neutral water, H⁺ is scarce at about 10⁻⁷ mol/L, so it does not play the main role.
These are local cells.
When local cells form on an iron surface in neutral, aerate…Faraday's law of electrolysis Galvanic corrosion Passivity Pitting corrosion Sacrificial anode Standard electrode potential Stress corrosion cracking