Corrosion & Environmental Degradation
Table of Contents
Electrochemical Processes 
· The diagram illustrates an electrochemical reaction occurring at the surface of a metal covered with a film of water containing dissolved oxygen. The two reactions involved in the corrosion are shown. Metal atoms dissociate into metal ions and free electrons in the oxidation reaction at the anode. These electrons migrate in the metal and initiate the reduction reaction at the cathode that generates the hydroxyl ions.
· The oxidation and reduction reactions are in balance such that, for the case illustrated, two metal ions go into solution for every four hydroxyl ions produced. The slowest reaction rate controls the overall corrosion rate.
· Other reduction reactions are possible, and several may occur simultaneously in a real corrosion process.

From: mechani1.htm