CORROSION CONTROL.

Abstract

The course on High Temperature and Corrosion Resistance of Metals is divided into two main topics: corrosion and oxidation, the difference between the two being presence of water in corrosion and its absence in oxidation. Of these two topics, corrosion receives the greater attention because of the variety of situations in which it occurs and the diverse characterizations of the damage associated with it. The electrochemical basis of the corrosion reaction is developed beginning with a review of thermodynamics. The corrosion cell is compared to electrochemical devices such as the battery, fuel cell, and electrochemical cell for producing reactions. The corrosion cell is analyzed thermodynamically by means of the Nernst equation. The eight types of corrosion damage as classified by M. G. Fontana and N. D. Greene are listed. The characteristics of each type, examples of the damage, and suggested preventative measures are discussed. Next, the kinetics of the corrosion reaction are introduced. Polarization behavior (activation and concentration) are shown to be a result of the kinetic limitations of the reactions. These fundamentals lead to the development of corrosion rate calculations and measurements from polarization behavior. Passivity is also discussed at some length. Then the five main methods of controlling corrosion are introduced to the students (cathodic protection, anodic protection, coatings, inhibitors, alloying). Each of these methods is related to the basic electrochemical thermodynamic and kinetic relationships described earlier in the course. Finally, the oxidation of metals is treated with emphasis on the processes involved and the controlling mechanisms in film formation and growth.