Which metals are commonly used for sacrificial protection to protect a more noble metal in seawater?

Which metals are commonly used for sacrificial protection to protect a more noble metal in seawater?

• A. Copper, nickel, or chromium
• B. Iron, steel, or lead
• C. Magnesium, aluminium, or zinc
• D. Gold, silver, or platinum

Answer: (C)

Sacrificial protection relies on using a more active metal to corrode in preference to the metal you want to shield. In seawater, the metals chosen for this role are magnesium, aluminium, or zinc. They have a more negative electrochemical potential than common naval metals like steel, so when they’re connected to the structure, they preferentially oxidize. This means they corrode away instead of the protected metal, keeping the more noble metal safer from corrosion. The other metals listed aren’t used for this purpose in seawater. Copper, nickel, and chromium are relatively noble and are typically used as coatings or in alloys rather than as consumable anodes. Iron and steel are usually the protected structure, not the sacrificial material. Lead is less effective as an anode and toxic, and gold, silver, and platinum are very noble and do not corrode to sacrifice themselves in practical protection systems.

Sacrificial protection relies on using a more active metal to corrode in preference to the metal you want to shield. In seawater, the metals chosen for this role are magnesium, aluminium, or zinc. They have a more negative electrochemical potential than common naval metals like steel, so when they’re connected to the structure, they preferentially oxidize. This means they corrode away instead of the protected metal, keeping the more noble metal safer from corrosion.

The other metals listed aren’t used for this purpose in seawater. Copper, nickel, and chromium are relatively noble and are typically used as coatings or in alloys rather than as consumable anodes. Iron and steel are usually the protected structure, not the sacrificial material. Lead is less effective as an anode and toxic, and gold, silver, and platinum are very noble and do not corrode to sacrifice themselves in practical protection systems.