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Galvanised Plating on Cable Containment - Sacrificial Anode?

CSkinner

I've been learning about sacrificial anodes recently.

I was given a formula to calculate how long a sacrificial anode will last; using the total mass, atomic mass and ionic charge of the sacrificial material, as well as the electrical current running through the anode.

It brought my attention to Galvanised steel basket tray.
Galvanised steel has a covering of Zinc[2+] to protect the steel from the environment; and it would also have an induced current from cables running along it.

But would there be a Cathode to complete this circuit? Perhaps where the containment is grounded?
It would be interesting if grounding the containment actually accelerates the decay of the zinc.

Any thoughts would be appreciated.

Thanks

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    Be aware that AC does not work like  this, more or less the same amount of metal is removed on one half cycle that is put back when the polarity reverses.

    In any case, trunking and similar is not normally buried or immersed in the way that would be necessary to complete the circuit.

    Mike.

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    Hi Mike,

    Thanks for the response!

    Wouldn't it be in a perfect model that the same amount of metal is removed on one half cycle and then put back on the other half? In the real world could you expect an imperfect sine wave that could strip more of the zinc than it inevitably puts back on?

    But on the other-hand how would that work? 
    In the positive half cycle, the Zinc would be stripped off and converted to Zinc Oxide; the negative half cycle wouldn't be able to strip the oxygen from the Zinc, would it? (asking out of ignorance, here)

    I guess my question was more about if a weak capacitor could be formed between the steel containment and a Ground connection; in my mind if it does then it matches the sacrificial anode model, and (maybe along with an imperfect sine wave) you would get accelerated decay of the zinc at the grounding points.

  • 0

    on the positive half cycle, the Zinc would be stripped off and converted to Zinc Oxide; the negative half cycle wouldn't be able to strip the oxygen from the Zinc, would it? (asking out of ignorance, here)

    well yes it can, and must - and capacitive coupling cannot pass a net DC. Equilibrium always has net zero charge transfer over a full cycle.

    Mike.

    PS Zinc is often extracted by electrolysis from solutions, and pulling zinc from sulphates and so on is very similar to separating oxides.

     

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