Rust is the name of iron oxides that forms when iron corrodes and is caused by the reaction of iron with oxygen. Rust is formed when oxygen dissolved in water reacts with iron. There are always two different reactions in a corrosion process:
1) oxidation of Iron
2Fe ---> 2Fe2+ + 4e-
2) reduction of Oxygen
O2 + 4 e- + H2O ---> 4OH-
The overall reaction is:
2Fe2+ + 4OH- ----> 2Fe(OH)2
Fe(OH)2 reacts with oxygen to form Iron oxides: Fe2O3 (hematite, red rust), Fe3O4 (magnetite, black)
