Eli5 How come some metals rust and others don’t?
In: Chemistry
Most, if not all metals will form an oxide layer where the bare metal contacts the atmosphere and reacts with oxygen. On most metals though, the oxide layer stays well attached to the base metal. One ferrous metals (Iron and steel), the oxide layer doesn’t adhere as well to the metal and can flake off, exposing fresh metal that can form another oxide layer and flake off again. This is why steel and iron typically need some protective coating or maintenance to prevent rusting. Stainless steels try to get around this by adding nickle and chromium, which can form well attached oxide layers and protect the iron from oxygen. Iron oxide in specific is what we call rust. Other metals can corrode under different circumstances, but that’s not chemically rust.
There are other factors that can corrode metals beyond just oxygen though. Contact between dissimilar metals can result in a galvanic reaction where one metal causes the other to oxidize. This can also be used to protect metals though. It’s not uncommon for zinc to be used to protect steel, since the galvanic reaction will cause the zinc to corrode before the steel.
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