Letter 40056

Zinc Iron Plating [India] 

March 27, 2006

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

Hello, Mr. Kumar. Please describe your own situation rather than framing your inquiry in the abstract. It makes the questions more interesting and more answerable--both of which lead to greater reader participation and a better chance of your receiving the help you need.

The reason that iron and steel corrode so readily is not because of their electrochemical activity 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, the oxidation product of steel is a fluffy, powdery, porous, water retaining rust which does nothing to seal the component 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 as being closer to steel than non-alloyed zinc plating, and we have the opportunity for slower corrosion of the plating and better corrosion resistance.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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