TABLE OF CONTENTS When metals are exposed to atmospheric conditions they react with air or water in the environment to form undesirable compounds, usually oxides. This process is called corrosion. Almost all metals except the less reactive metals such as gold, platinum, and palladium, undergo corrosion. For example, silver tarnishes, copper develops a green coating, lead, and stainless steel lose their lustre to corrosion. Thus, corrosion may be defined as the gradual eating away, disintegration, decaying, or deterioration of a metal by a chemical or electrochemical reaction with its environment.
This theory is based on Nernst theory, according to which all metals have a tendency to pass into solution. The tendency of a metal to pass into solution when immersed in a solution of its salt is measured in terms of electrode potential. If a metal having higher electrode potential comes into contact with another metal having a lower electrode potential, a galvanic cell is set up and the metal having the higher electrode potential becomes anodic and goes into solution to a measurable extent. The extent of galvanic corrosion depends upon the difference in the electrode potential of the two electrodes and their respective areas. The greater the difference in the potentials of the cathode and anode, the greater will be the corrosion. Also the smaller the area of the anode as compared to the cathode, the more will be the attack.
Corrosion reactions. The...
