Quote:
Originally Posted by ColinTheAmpMan1
Glyn, as far as I'm aware, passivation of zinc is what happens when galvanised (zinc plated) iron slowly oxidises. If you try to paint galvanised iron while it is still bright, the paint will quite quickly peel off, leaving an ugly mess. If the zinc plating is allowed to oxidise slowly and form a matt patina, the paint will stick to this much better. This is why you often see street lamps, roadsigns and other street furniture made of galvanised iron remaining unpainted for a while.
It could be that there is another process, though...
Colin.
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In metallurgical terms passivation refers to the process whereby a metal surface becomes more passive, i.e. less prone to corrosion. This can be as you say an oxidation process whereby an oxide film builds up and protects the surface or it can be a process of adding a protective layer but generally when people refer to passivated zinc they mean an additional protective layer, usually a chromate based process, that is carried out after the zinc plating. A good example would be the yellowish colour that you often see on plated nuts and bolts, this is a type of passivated zinc finish.