Why do we galvanise steel? Galvanised steel is steel coated with zinc.
it prevents the steel from rusting. Zinc rusts too, but more slowly than steel, and it doesn't tend to eat away it's structure. Zinc coatings prevent oxidation of the protected metal by forming a barrier, and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminium and stainless steels by their oxide layers.
The coating of zinc inhibits rust. First of all the zinc does not oxidize a readily as iron (steel). If the zinc coating gets scratched it still protects the exposed iron. When the zinc and exposed iron get wet they behave like a battery. Electrons flow from the zinc layer to the iron layer. The extra electrons in the iron layer replace any that might be lost to oxidation and help keep the iron metallic. Of course now the zinc oxidizes faster so eventually all of the metallic zinc is removed and the iron is unprotected and will rust. The fact that the zinc doesn't have to cover the steel is shown in another process. To protect the steel hulls of ocean going ships a block of zinc is attached to the bottom. The electrical circuit behaves as described above. When the zinc block has dissolved they just attach another one. If they keep this up the hull of the ship remains corrosion free. A tin coating on steel (as in a tin can) works just the opposite. When the tin is scratched the electrons flow from iron to tin so the iron rusts faster than it would have with no tin.
Keeps it from rusting. Zinc doesn't rust like steel does.
We galvanize steel to protect and prevent steel from rusting or corrosion. Rusting, for the most part is a layman's term that has been used exclusively to describe the chemical OXIDATION reaction of steel or iron with oxygen forming a reddish brown substance called rust. Zinc metal coating also oxidizes but does not form the reddish brown rust. Instead, it forms an oxide, just like the rust, which is iron oxide. The protection created by zinc is because it is more reactive to oxidizers, than steel or iron. Thus, the oxidizer will react with Zinc first before it will react with Iron, hence protecting iron. If the zinc is fully reacted then iron is next. BUT, the zinc oxide formed on the surface of the steel or iron is no longer reactive to oxygen and also creates a good physical barrier so that oxygen will not have chance to even have contact with the underlying steel. Isn't that neat! Here is chemistry at one of its useful best.
