What Causes Rust?

The reddish-brown crust that often forms on iron and steel objects comes from changes that take place in the outer surface of the metal itself. This crust, called rust, is caused by the mixture of the metal with oxygen from water in the air.

rusting car

When moisture from the air, or from anywhere else, reaches an object with iron in it, oxygen in the water combines with atoms of iron to form molecules of a compound called iron oxide.

The iron oxide particles remain suspended in the water, but when the water evaporates, the particles remain, forming a reddish coating on the surface of the iron. Without the presence of water, objects cannot rust.

Other metals besides iron and steel can rust when exposed to moisture, but not all rust is “rust-colored.” For instance, when copper or bronze rusts, it turns green. The green crust is called a patina.

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

7 thoughts on “What Causes Rust?”

  1. is not necessary that water evaporates to have rust deposits. rust formations is a complex series of reactions that finally leads to what is called rust Fe2O3 (red iron oxyde)

  2. No, carbon dioxide has both carbon and oxygen, but iron oxide only requires pure oxygen to be produced by the oxygen and iron molecules. The oxygen is mixed with the carbon in carbon dioxide.

  3. ok I am fixing to help my son on a science project and we will see what will make metal rust the quickest. water saline (salt water) coke the drink, vinegar. I know some of these things can clean but we will see if they rust it at all I should know something in about 3 weeks. if anyone knows these answers or has info on it he has to do a research paper and would love more info.

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