Corrosion Technician Practice Exam

Concentration-cell driven corrosion occurs when two regions on the same metal surface are in contact with electrolytes that have different metal ion concentrations. In a crevice, dissolution releases metal ions and diffusion is restricted, so the ion concentration inside the crevice differs from the bulk solution. This creates a local electrochemical potential difference, causing the area inside the crevice to behave anodically and dissolve while the outside acts as the cathode. The result is localized attack right at the crevice opening. Other forms don’t fit as well: an oxygen concentration difference drives differential aeration corrosion, filiform corrosion is a coating-related surface path, and uniform corrosion involves a generally even attack rather than a localized, ion-concentration-driven process.