Chronoellipsometry: a new technique for the study of anodic processes of the dissolution-precipitation type

Abstract

Conventional chronopotentiometry cannot be used for partially or totally diffusion-controlled anodic processes in which the precipitation of an insoluble salt (resulting from accumulation of products of metal dissolution) is not accompanied by a rapid potential increase. The new technique of "chronoellipsometry" permits the optical monitoring of film formation on the surface of a mirror anode and the registering of the time interval (called the "induction time") between imposition of the anodic current and the formation of a precipitate. In order to analyze the induction time data, the diffusion problem has been solved under the appropriate boundary conditions. It is shown that the nature of the it vs i plot will reveal whether the ionic product of anodic electrolysis participates in a homogeneous chemical reaction. Further, the equilibrium and rate constants for the homogeneous reaction can be obtained.