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I have a school experiment wherein I will put aluminum coating to a steel substrate, wherein the Al will act as a corrosion protector for the steel. We know that aluminum is also classified as a sacrificial anode. Can the aluminum coating on the steel provides a cathodic protection?

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In practice, no -- at least, not at ambient temperature. Aluminum passivates and this passive film breaks the potential electrochemical circuit. The passivated aluminum can't react to release electrons to the steel. For cathodic protection you need something that will corrode instead of the steel, meaning it can't passivate.

Usually, cathodic protection is offered by zinc which has less driving force, but it does not passivate and thus the electrochemical circuit remains intact.

Addendum:

Aluminizing does offer cathodic protection at high temperature where the passivation is less effective.

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  • $\begingroup$ So the corrosion protection that Al coating provides for steels cannot be considered a cathodic protection? $\endgroup$ – Acid May 20 '17 at 11:52
  • $\begingroup$ That is right, at least under ambient conditions. Aluminizing is more effective at high temperature where the aluminum finally becomes more reactive. See onealsteel.com/carbon-steel-sheet-aluminized.html. $\endgroup$ – Oscar Lanzi May 20 '17 at 12:00
  • $\begingroup$ I have read about this concept. So if the aluminum coating on steel passivates, it can provide great corrosion protection for the steel, although this process can't be considered cathodic protection, right? $\endgroup$ – Acid May 22 '17 at 9:54
  • $\begingroup$ Not cathodic protection, right. $\endgroup$ – Oscar Lanzi May 22 '17 at 10:04

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