| MadSci Network: Chemistry |
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 nails. 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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