If the cathodic area is much larger than the anodic area, what is the expected effect on the accelerated corrosion rate of the anodic metal?

• A. Increase
• B. Decrease
• C. No change
• D. Reverse

Answer: (A)

In galvanic corrosion, the rate at which the anodic metal dissolves is set by the total electrochemical current flowing between the two metals. When the cathodic area is much larger than the anodic area, the cell can carry a larger cathodic current at the same driving conditions. That larger current pulls more electrons from the anodic metal, causing more metal atoms to oxidize per second. In short, the anodic dissolution rate increases as the cathodic area grows, so the corrosion of the anodic metal is accelerated. If the cathodic area were smaller or similar, the total current would be lower and the anodic corrosion would be slower.