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Letter 40056
Why is Zinc Iron Plating better than Zinc
Plating?
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I have a doubt. How adding Iron to zinc will improve the corrosive
resistance since iron oxide is a rust.
J.Vinoth Kumar
- Coimbatore, Tamilnadu, India
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Hello, J. Vinoth. Please try to describe the situation you find
yourself in rather than describing your question in abstract terms.
It makes the questions more answerable -- which leads to greater
reader participation and a better chance of you receiving the help
you seek.
The reason that iron and steel corrode so readily is not because
of their electrochemical activity (actually iron is less active than
zinc or aluminum) but because the corrosion products are not
adherent, tenacious, and impervious to further degradation. While
some other metals can form a nice tight tarnish or oxidation product
that seal the metal surface fairly well, the oxidation product of
steel is a fluffy, powdery, porous, water retaining rust which does
nothing to seal the underlying steel away from the environment. But
the corrosion product of a zinc-iron alloy plating is not a fluffy
rust, but a reasonably stable oxidation product.
Once that is recognized, we can go on to look at the
electrochemical potential of zinc-iron and recognize it as being
closer to steel than non-alloyed zinc plating. Now the galvanic
potential between the steel and the plating is lower, and we have the
opportunity for slower corrosion of the plating and better corrosion
resistance.
Please come back with a followup if I wasn't clear. Good luck.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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