The galvanised article is protected against rusting even if the zinc coating is broken.How does it happen?
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There are two ways that Zn can protect, say iron articles.
First if the iron is totally dipped in molten zinc, it gets a thorough coating of zinc. The zinc tarnishes, and that tarnish adheres so well that corrosion in iron cannot continue further.
But, when the coating is broken, & the iron is exposed to the atmosphere then it will get corroded.
Since zinc is "more active" than iron. This is because zinc being more reactive reacts with the oxygen and water in the atmosphere even if the layer of zinc is broken all of the zinc must corrode before the iron.
The more active metal corrodes first, as long as the 2 metals are still connected somewhere forming sacrificial anode.
First if the iron is totally dipped in molten zinc, it gets a thorough coating of zinc. The zinc tarnishes, and that tarnish adheres so well that corrosion in iron cannot continue further.
But, when the coating is broken, & the iron is exposed to the atmosphere then it will get corroded.
Since zinc is "more active" than iron. This is because zinc being more reactive reacts with the oxygen and water in the atmosphere even if the layer of zinc is broken all of the zinc must corrode before the iron.
The more active metal corrodes first, as long as the 2 metals are still connected somewhere forming sacrificial anode.
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