Why galvanised item always protected from rust?

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In my science textbook it is written that even after the zinc layer in galvanised articles is broken, the items remain invincible to rust.

Why is it like that? How come it could not rust after losing the protective layer?
 
Chemistry news on Phys.org
http://en.wikipedia.org/wiki/Galvanization

Galvanizing protects in two ways:

-it forms a coating of corrosion-resistant zinc which prevents corrosive substances from reaching the more delicate metal
-the zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still be protected by the remaining zinc.
 
aroc91 said:
http://en.wikipedia.org/wiki/Galvanization

Galvanizing protects in two ways:

-it forms a coating of corrosion-resistant zinc which prevents corrosive substances from reaching the more delicate metal
-the zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still be protected by the remaining zinc.

I am with the OP on this one.
Galvanization works but how.

Protective, you mean like paint?
Sacrificial anode - what does that mean?

Most descriptions are of the type given by the Wiki, which with a lot of words, says little, leaving out the physics and chemical description, with the reader still not any wiser.

maybe a better approach is to ask and answer
So why zinc?
Why not copper?
 
256bits said:
I am with the OP on this one.
Galvanization works but how.

Protective, you mean like paint?
Sacrificial anode - what does that mean?

Most descriptions are of the type given by the Wiki, which with a lot of words, says little, leaving out the physics and chemical description, with the reader still not any wiser.

maybe a better approach is to ask and answer
So why zinc?
Why not copper?

Research is like tracing a thread from a spider web: you start off wanting to know how galvanization works, and this leads to a discussion of galvanic action, then to anodes and cathodes, then to ...

You've got to start somewhere, but this doesn't mean necessarily that you can make only one stop along this path and gather all of the information to answer your question.