What makes iron and steel rust?
Rust is a generic term to describe a series of different oxides, Fe(OH)2, Fe(OH)3, FeO(OH), Fe2O3.H2O that form when iron corrodes.
The common form of Rust is a Red products:Fe2O3.
Rust forms due to a reaction between the iron and water; either water condensing from air or rain.
The oxygen in the air dissolves in the water and causes rust to form. There are always two distinct chemical reactions in a corrosion process, the basic chemistry of corrosion is:
1) Anodic Dissolution of Metal (Iron) that goes into solution (water)
Fe -----> Fe2+ + 2e-
2) Cathodic Reduction of Oxygen dissolved in water
O2 + 2H2O + 4e- ---->
4OH-
The final reaction is:
Fe2+ + 2OH- -----> Fe(OH)2
This oxide will then further reacts with oxygen to give the final red product:
Fe2O3.H2O
