A Salt Layer Model for the Active Anodic Dissolution to Passive Transition of Nickel in Presence of Chloride

摘要

The active/passive transition of nickel in an acid medium which contains chloride ions is analyzed by means of a theoretical model which considers a nickel chloride salt layer precipitation coupled with a nickel ion diffusion process away from the electrode surface. There is obtained a good agreement between experimental and calculated impedance spectra. From this simulation procedure it is observed that the polarization curves shape is a consequence of the surface fraction blocked by salt layer (θ{sub}b) that depends on the applied potential. Moreover, variations in salt properties with the stabilization potential cannot be neglected since it is necessary to consider a continuous decrease in diffusion layer thickness (δ).