Use of Ellipsometry in the Study of Corrosion

Because corrosion processes are strongly affected by the presence of thin films, ellipsometry is an especially valuable tool in corrosion research because it allows observation of film formation, dissolution, or property changes while these phenomena actually are occurring on a metal surface immersed in any transparent environment. Experimentally the use of ellipsometry requires that light be reflected from the corroding or passive metal surface under study. Thus it allows other techniques such as electrochemical ones to be carried out simultaneously along with ellipsometric measurements. The following specific examples serve as a small sampling of the many ways in which ellipsometry has been applied to corrosion studies: (1) Determination of the nature and rate of growth of passive films on iron in inorganic inhibitor solutions. (2) Separation of different stages in the early growth process of films formed by potentiostatic anodic polarization on iron in neutral solutions. (3) Determination of the point in the corrosion of copper when a new phase begins to form in the corrosion product film.