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What is Rust?

 

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What is Rust?

 

Rust is a generic term used to describe different iron hydroxides and 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 called hematite. What causes Rust to form is the reaction between iron and water; for iron exposed to the atmosphere it could be 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 iron hydroxide will then further reacts with oxygen to give the final red product (Rust):

Fe2O3.H2O

iron corrosion, mechanism of iron corrosion

 

     
 

see also:

What is Corrosion?

Corrosion Types

What causes rust?

What is the best rust converter?