Qualitative use of ellipsometry to study localized corrosion processes

Abstract

Localized corrosion processes such as pitting, intergranular corrosion, crevice corrosion, and stress corrosion involve many aspects that are not amenable to a quantitative study by ellipsometry. This paper describes uses of ellipsometry that can, however, provide valuable insights into localized corrosion processes without having to determine the optical constants of absorbing films. The uses described are as follows: (1) the determination of induction times for pit initiation and the demonstration that changes occur in the passive film prior to pitting; (2) the measurement of the rate of repassivation, a process of importance to stress corrosion, for a metal surface whose protective film has been removed by abrasion (triboellipsometry); and (3) the identification of three stages leading to crevice corrosion by ellipsometric measurements made within a crevice.