MadSci Network: Chemistry

Re: Chemical analysis for galvanized nails

Date: Tue Aug 24 12:55:54 1999
Posted By: Joseph Weeks, President, Thermal Products, Inc.
Area of science: Chemistry
ID: 934919359.Ch

Galvanized nails are a composite system consisting of a steel nail coated 
with a protective layer of zinc.  Typically the steel nail is made of a low 
carbon steel which chemically is iron with about 0.2 percent carbon.  The 
size and distribution of the carbon particles in the iron determines the 
strength and hardness of the steel.
The coating on the nails is a layer of zinc, which can be applied by hot 
dipping the nails in molten zinc, or by electroplating.  The hot dipped 
nails typically have a much rougher, thicker coating than the electroplated 

Zinc protects iron from rusting through an electrochemical process, the 
same type of process which generates electrical current in batteries.  
Batteries used to be called "galvanic cells."  In the galvanic series, zinc 
is more electronegative than is iron, meaning that zinc will corrode more 
easily than iron.  When exposed to moisture, the zinc corrodes to form a 
white powdery coating of zinc oxide while protecting the iron from forming 
red iron oxides.  After some time, the zinc is all oxidized, so there is no 
longer "galvanic" protection for the iron.  As a result, the iron or steel 
suddenly appears to start rusting all over.  Hope this information helps.

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