What happens when a pit fills with corrosion products?

• A. Increases internal resistance and can terminate growth
• B. Increases propagation rate
• C. Has no effect
• D. Decreases cathodic area

Answer: (A)

When a pit fills with corrosion products, the path for ion movement inside the pit becomes more restricted. Those solid corrosion products (like oxides and hydroxides) block diffusion of reagents such as oxygen to the metal surface and hinder the flow of ions within the pit. That raises the internal resistance of the pit and slows the electrochemical reactions driving dissolution. With higher resistance and limited supply of oxidants, the current that sustains pit growth drops, so the pit is more likely to stop growing or even terminate. This is why increased internal resistance and potential cessation of growth is the most accurate description.