Problem 7.10: Using Ohms Law applied to the corrosion cell
From Chapter 7 Problem Set. Level 3: System Integration.
Question
Using Ohm’s Law applied to the corrosion cell (Current = Voltage / Resistance), explain why pitting accelerates once a passive film is breached. Address both the voltage and resistance terms.
Answer
Show answer
When the passive film is breached, resistance drops because the protective barrier no longer impedes electron transfer and ion migration. Simultaneously, voltage increases because the exposed bare metal has a much lower reduction potential than the surrounding passivated surface, creating a large potential difference. By Ohm’s Law, lower resistance and higher voltage both drive higher current. That current concentrates on the small exposed anode, producing the intense localized dissolution that defines pitting.