Which statement best describes galvanic corrosion when two metals are in contact in an electrolyte?

• A. Dissimilar metals in contact in an electrolyte create a galvanic cell.
• B. Two identical metals in contact with air
• C. A single metal in a vacuum
• D. Metal and ceramic in dry contact

Answer: (A)

Galvanic corrosion happens when two different metals touch each other in an electrolyte. Because the metals have different electrochemical potentials, electrons flow from the more active metal (the anode) to the less active metal (the cathode) through the metal connection, while ions move in the electrolyte to balance charge. This causes the anodic metal to dissolve faster, accelerating its corrosion, while the cathodic metal is relatively protected. The electrolyte is essential because it provides a medium for ion movement and completes the electrical circuit.

If metals are identical, or if there is no electrolyte (as in dry air or a vacuum), the driving force for this electrochemical reaction isn’t present, so galvanic corrosion doesn’t occur. Likewise, a metal in dry contact with a ceramic won’t undergo galvanic corrosion due to the lack of a conductive path for ions and electrons. Therefore, the scenario of dissimilar metals in contact in an electrolyte best describes galvanic corrosion.