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What is Rust?

Rust is a generic term to describe a series of different oxides, Fe(OH)2, Fe(OH)3, FeO(OH), Fe2O3.H2O that forms 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 into 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

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