Crevice corrosion is driven by which mechanism?

Crevice corrosion is driven by which mechanism?

• A. Dissimilar metals in contact with electrolyte
• B. Coating defects
• C. Ion concentration differences in electrolyte
• D. Temperature gradient

Answer: (C)

Crevice corrosion happens because a crevice creates a restricted diffusion path for the electrolyte, so ions build up and deplete differently inside the crevice than in the surrounding solution. Inside the crevice, oxygen is drawn down because it diffuses in slowly and is consumed, leaving a low-oxygen, high-chloride, acidic environment. This difference in ion concentrations sets up a localized galvanic cell: the metal inside the crevice tends to dissolve (anodic) while the area outside acts more like a cathode. The result is accelerated metal loss specifically within the crevice, driven by the concentration differences of ions in the electrolyte, not by contact with dissimilar metals, coating defects alone, or a temperature gradient.

Crevice corrosion happens because a crevice creates a restricted diffusion path for the electrolyte, so ions build up and deplete differently inside the crevice than in the surrounding solution. Inside the crevice, oxygen is drawn down because it diffuses in slowly and is consumed, leaving a low-oxygen, high-chloride, acidic environment. This difference in ion concentrations sets up a localized galvanic cell: the metal inside the crevice tends to dissolve (anodic) while the area outside acts more like a cathode. The result is accelerated metal loss specifically within the crevice, driven by the concentration differences of ions in the electrolyte, not by contact with dissimilar metals, coating defects alone, or a temperature gradient.