The Corrosion of Metals-I. Mechanism of Corrosion Processes

Abstract

This paper outlines the application of electrochemical methods to corrosion investigations. It discusses the position of the potential of a metal against its environment and the trend of this potential with time, pointing out that it is thereby possible to determine whether the corrosion process is controlled by reactions occurring at the anodic areas, the cathodic areas, or both; that is, whether there is a tendency toward passivity, inhibition or progressive attack. Measurements of film stability whether in terms of the leakage current which may be passed through the film or in terms of the amount of film forming material required to produce passivity or the amount of film destroying material required to render a metal active, furnish information as to the quality of corrosion resistant films. Measurements of the rate at which a film forms on a metal when placed in a film-forming environment throws light on its relative surface reactivity, and such information is of assistance in determining the rate of corrosion in homogeneous corrosive environments or the rate of passivation in the film-forming environments. On the basis of such measurements and with a chemical knowledge of the environments in which metals are used as well as the composition and physical state or structure of the metals, it is possible to predict corrosion behavior and to obtain an understanding of corrosion problems usually not possible by ordinary empirical corrosion tests.