Cathodic Protection

Sacrificial anodes are used to protect another metal from corroding. A metal with a more negative standard reduction potential is attached to the desired metal to protect it. This creates a galvanic cell were the desired metal is the cathode. The sacrificial anode will corrode leaving the cathode intact.

To show this, two cells were set up using iron nails and either zinc or nickel. The electrodes were connected by copper wire and placed in ~500mL of tap water.

Metal Standard Reduction Potential (V)
Iron -0.44
Nickel -0.25
Zinc -0.76

 

Since Zinc has a more negative standard reduction potential than Iron, it corroded. Iron has a more negative standard reduction potential than Nickel so Iron corroded in that cell.

Image

Figure 1 Iron and Zinc cell. Zinc corroded although it is hard to tell since zinc oxide is white

Image

Figure 2 Iron and Nickel cell. Iron is corroded.

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