If the cathodic surface area is increased relative to the anodic surface area, what happens to the corrosion rate of the anodic metal?

If the cathodic surface area is increased relative to the anodic surface area, what happens to the corrosion rate of the anodic metal?

• A. It increases
• B. It decreases
• C. It remains the same
• D. It becomes unpredictable

Answer: (A)

In galvanic corrosion, the anodic metal dissolves at a rate tied to the galvanic current flowing between the two metals. If the cathodic surface area becomes larger relative to the anodic area, the alloy pair can carry more current for the same potential difference. That extra current must be supplied by the anodic metal, so the total anodic dissolution increases. With a fixed anodic area, the higher total current translates into a higher current density on the anode, accelerating its corrosion. So the anodic metal corrodes faster when the cathodic area is increased.

In galvanic corrosion, the anodic metal dissolves at a rate tied to the galvanic current flowing between the two metals. If the cathodic surface area becomes larger relative to the anodic area, the alloy pair can carry more current for the same potential difference. That extra current must be supplied by the anodic metal, so the total anodic dissolution increases. With a fixed anodic area, the higher total current translates into a higher current density on the anode, accelerating its corrosion. So the anodic metal corrodes faster when the cathodic area is increased.