How come rust built up on iron things looks like a thick crust, but somehow when it's removed it's like there's nothing gone from the original?
How come rust built up on iron things looks like a thick crust, but somehow when it's removed it's like there's nothing gone from the original?
often there is stuff gone, called pitting
Full disclosure, I’m not an expert in any scientific field, but I did have to read up on this in school one.
The gist of it is that iron is a solid at most temperatures found on earth, and other materials don’t penetrate it easily. Rust is formed by a chemical reaction of oxygen and iron, where the oxygen binds with the iron.
Rust is also a solid at most temperature found on earth though, meaning when enough rust coats the surface of an iron object, much like paint, the oxygen cannot easily reach the iron underneath, leaving it unchanged.
Over time, things could come along and cause that rust to erode away, which would then lead to more of the iron being exposed and more rust forming, but that takes time. Thus with larger iron objects, you’ll still typically find iron underneath.
Thank you for your answer. I guess I could've done some more research myself, but I was also interested if I wasn't the only one who wondered about it.
I keep getting these videos on TikTok where someone finds an old axe, completely caked in thick layers of rust, and at the end of their magic you can sometimes even see the stamp of the original maker. Truly baffling.
Because the rust is very fluffy, while the iron is very dense. So a very small volume of iron can turn into a large volume of rust.
The iron is disappearing though. Just slowly. You could tell if you weighed it with a sensitive scale.
To add to this, rust is only about 70% iron by mass, with the remainder being oxygen. So the rust basically weighs a bit more than just the iron used to create it.