Investigations of the electroreduction process of anodic films grown on tin in carbonate-bicarbonate solutions

Combined voltammetry and potentiostatic current transient techniques have been employed to study the electroreduction process of composite surface layers anodically formed on high purity polycrystalline tin in carbonate-bicarbonate ion containing solutions. The dynamic system analysis performed by using parametric identification procedures and non-linear fit routines has demonstrated that data obtained under a wide variety of experimental conditions can be interpreted by taking into account the participation of various Sn(II)/Sn(IV)-containing surface species. Thus, the electroreduction of passive layers formed at relatively low potentials can be explained through an instantaneous nucleation and 3D growth mechanism controlled by diffusion of OH- ions away from the reacting interface, whereas for surface layers produced at high positive potentials where the formation of SnO2 predominates, the electroreduction follows a progressive nucleation and 3D growth process under charge transfer control. The influence of anodizing time at different potentials as well as effects due to surface layer thickness can be discussed on the basis of electroreduction reaction models. Copyright (C) 1996 Elsevier Science Ltd