Galvanic corrosion is most rapid when the anodic area is smaller than the cathodic area.

• A. True
• B. False
• C. Not determinable
• D. Only under extreme conditions

Answer: (A)

Galvanic corrosion happens when two dissimilar metals are connected in an electrolyte; one acts as the anode and dissolves, while the other acts as the cathode. The rate of the anode’s corrosion is driven by the galvanic current, which is influenced by the cathode’s area. A larger cathodic area sinks more current, so the same total current passing through a smaller anodic area results in a higher current density (current per unit area) on the anodic surface. That higher current density accelerates the dissolution of the anodic metal, making corrosion more rapid when the anodic area is smaller than the cathodic area. If the anodic area were large relative to the cathode, the current density on the anodic surface would be lower and the rate would be slower. Real-world factors like electrolyte, temperature, and coatings can modify rates, but the area ratio is the key determinant here.