To answer this question, lets establish that rust is a product of combustion.
Isn’t combustion what happens when something burns? Well, yes. But more specifically it’s what happens when something reacts with oxygen to produce heat and light, as in fire.
So what’s fire got to do with rust?
They are both a combustion reaction. Like a fire, the combustion reaction produces heat. Actually, it’s the same amount of heat, but because it’s spread out over a much longer time, it cools off at the same time it’s heating up. Certain metals, iron for instance, if in contact with oxygen, reacts with the oxygen, but a whole lot slower, and without making a flame. Iron plus oxygen makes iron oxide. And that’s what we call rust.
Adding water speeds up this reaction so the iron rusts a lot quicker.
Dry ice blasting will remove rust from metal, but the underlying chemically etched surface created by the rusting process will not be changed, leaving the metal surface clean but pitted. If you are looking for a smooth metal finish, you may not get it. To do that you have to remove the surface metal, something the dry ice blasting process cannot do. But that can be good too, because it reserves the surface integrity of the metal.
Assuming you are trying to keep something made of iron or steel from rusting, you need to keep the metal from coming in contact with oxygen. This particular rusted metal air compressor, pictured here, after dry ice blasting to remove the rust, was coated with epoxy to separate the metal from the effects of oxidation.
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