In metal ion concentration cell crevice corrosion the corrosion is usually concentrated at the ______ to the crevice.

• A. Entrance
• B. Inside
• C. Outside
• D. Tip

Answer: (A)

Crevice corrosion is driven by a metal ion concentration cell that forms when mass transport is restricted inside a crevice. The solution inside the crevice becomes depleted of oxygen and accumulates aggressive ions, creating a more acidic and conductive environment, while the solution outside remains richer in oxygen and more oxidizing. This sets up a potential difference between the interior and exterior surfaces, causing dissolution to be most intense where fresh solution meets the stagnant crevice—at the entrance to the crevice. There, the gradient is steepest and the electrochemical driving force for metal loss is strongest, so corrosion concentrates there.