Which of these materials is the most cathodic?

Which of these materials is the most cathodic?

• A. Zinc
• B. 2024 aluminum alloy
• C. Stainless steel
• D. Aluminum bronze

Answer: (C)

In a galvanic relationship, the metal that is more noble (more cathodic) in a given environment is the one that resists oxidation and acts as the cathode, while the less noble metal becomes the anode and corrodes. Zinc is highly active and readily oxidizes, so it tends to become the anode rather than the cathode. The 2024 aluminum alloy is also relatively active and prone to oxidation, so it’s not the cathode either. Aluminum bronze, while fairly corrosion-resistant due to copper, sits somewhere between these in terms of nobility, but stainless steel generally remains more noble because its chromium oxide passive layer makes it a more cathodic electrode in typical aqueous environments. Thus, stainless steel is the most cathodic among the options.

In a galvanic relationship, the metal that is more noble (more cathodic) in a given environment is the one that resists oxidation and acts as the cathode, while the less noble metal becomes the anode and corrodes.

Zinc is highly active and readily oxidizes, so it tends to become the anode rather than the cathode. The 2024 aluminum alloy is also relatively active and prone to oxidation, so it’s not the cathode either. Aluminum bronze, while fairly corrosion-resistant due to copper, sits somewhere between these in terms of nobility, but stainless steel generally remains more noble because its chromium oxide passive layer makes it a more cathodic electrode in typical aqueous environments.

Thus, stainless steel is the most cathodic among the options.