Oxygen Differential Corrosion

Definition

Oxygen differential corrosion arises from an uneven oxygen distribution, where a low-oxygen region becomes the anode and a well-aerated region becomes the cathode. Oxygen does not have to be high to be severe, only uneven.

Once a pit, crevice, gasket, or deposit forms, oxygen is starved inside while the surrounding metal stays well aerated, setting up high oxygen at the rim as the cathode and low oxygen at the base as the anode. A powerful potential forms in which the large cathode drives intense dissolution at the tiny anode, and chloride migrates in to balance charge, creating an acidic salt-rich soup that drills through metal quickly. This mechanism underlies under-deposit and crevice attack.

Related concepts

Current Density · Under-Deposit Corrosion · Pitting Corrosion

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Part of The Blueprint of Water · ⚡ electrochemistry