The impact of oxygen on corrosion corrosion

In the basic mechanism of iron corrosion, the oxygen in the air dissolves in water and causes rust (iron oxides) to form.

Four conditions must exist before electrochemical corrosion can proceed:

(1) there must be something that corrodes , the metal anode, where the oxidation reaction take places

(2) there must be a cathode, where the reduction reaction take places

(3) there must be continuous conductive liquid path (electrolyte, usually condensate and salt or other contaminations), for example: water, seawater, condensing water, humidity..

(4) there must be a conductor to carry the flow of electrons from the anode to the cathode.

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

see also:

what is corrosion

what is rust

what causes rust

Evaluation of Deoxygenation as a Corrosion Control Measure for Ballast Tanks