Which mechanism involves a difference in oxygen concentration between the area inside and outside a crevice, leading to a potential difference?

• A. Oxygen concentration cell corrosion
• B. Metal ion concentration cell crevice corrosion
• C. Localized corrosion
• D. Uniform corrosion

Answer: (A)

Oxygen concentration cell corrosion is the mechanism at play. In a crevice, oxygen can’t diffuse in freely, so the interior becomes depleted of oxygen while the exterior remains relatively oxygen-rich. That gradient creates two distinct electrochemical environments: the crevice interior tends to become anodic and dissolves metal, while the outer, oxygen-rich area acts as the cathode where oxygen reduction occurs. Electrons flow from the interior to the exterior through the metal, sustaining dissolution inside the crevice and maintaining the potential difference that drives the attack. The stagnant crevice electrolyte can also become acidic and chloride-rich, which speeds up the corrosion. This specific oxygen-driven potential difference is what defines this mechanism. While localized and crevice corrosion describe the broader phenomenon, the exact driver here is the oxygen concentration cell effect.