Eli5 How come some metals rust and others don’t?
In: Chemistry
Corrosion happens when a metal reacts with something. The most reactive “something” that most metals encounter is oxygen in the air, so most corrosion, including rust, is reaction with oxygen.
A metal corrodes if oxygen is able to rip electrons off it. Oxygen is good at that. It can corrode copper, iron, nickel, cobalt, zinc, aluminum, magnesium, calcium, strontium…a whole list. But not everybody.
Some metals have a strong enough grip on their electrons that oxygen can’t pull them off. You can find those metals on a ‘redox table’ – they include gold, iridium and platinum. It’s not a coincidence that many of them are metals we make jewelry out of – we do that because these metals stay shiny and bright.
Here’s a redox table. You can see at 0.40 volts, that’s the reaction that corrodes most metals, when they get exposed to oxygen and moisture at the same time. Every metal lower than that will corrode just from being outdoors; metals above that are much harder to corrode and will often be found as bright, shiny nuggets, even if they’ve been in the ground for thousands or millions of years.
http://ch302.cm.utexas.edu/images302/standard-potentials.png
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