What type of corrosion occurs when metals with different potentials are in electrical contact and exposed to an electrolyte?

• A. Filiform corrosion
• B. Intergranular corrosion
• C. Galvanic corrosion
• D. Uniform corrosion

Answer: (C)

When two metals with different electrode potentials are in electrical contact and immersed in an electrolyte, a galvanic cell forms. The metal with the higher potential (the cathode) conducts electrons, while the metal with the lower potential (the anode) loses electrons and corrodes faster. The electrolyte allows ion flow, completing the circuit and driving corrosion at the anodic metal. This is why dissimilar metals in contact in a corrosive environment often show accelerated attack on one metal and relative protection of the other.

Other corrosion types don’t fit this situation as neatly. Filiform corrosion happens under coatings as worm-like channels of attack, not due to a metal-to-metal electrical couple. Intergranular corrosion travels along grain boundaries in sensitized alloys, not because of dissimilar metals in contact. Uniform corrosion is general, even dissolution across a surface, and isn’t specifically driven by a potential difference between two different metals in contact.