Corrosionist  The Website of Corrosion Protection and Corrosion Control

 
You are here >>> HOME - Corrosion & Rust FAQ - What is rust?  
 

What is Rust?

 

Bookmark and Share

 

   

                                                  

What is Rust?

 

Rust is a generic term used to describe the result of iron corrosion.

Rust

In the picture above is easy to see the difference between steel with a coating/paint and without. The part with the coating has some small spots of rust where the coating is damaged, while the bare steel is completely covered by a layer of rust (corrosion products)

What is Rust made of?

Rust is made of different iron hydroxides and oxides, Fe(OH)2, Fe(OH)3, FeO(OH), Fe2O3.H2O that form when iron corrodes.

What is Rust Chemically

The common form of Rust is a Red products Fe2O3 called hematite.

How is Rust Formed

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

How to Prevent Rust

The most common and easy method that can be used to prevent rust formation is to apply a paint over the surface of the metal to be protected.

 

     
 

see also:

What is Corrosion?

Corrosion Types

What causes rust?

What is the best rust converter?