Mechanism of Electrochemical Dissolution of Nickel Grown by Carbonyl Method

A laboratory-grown nickel sample was used to investigate the galvanostatic dissolution under industrial electroplating conditions. The sample contained multiple layers corresponding to changes in the Ni(CO)4 decomposition temperature ranging from 200 to 280 °C. Cyclic voltammetry curves were used to determine the active dissolution, passive and transpassive potentials regions of the sample. Chronopotentiometric curves recorded during galvanostatic dissolution displayed oscillations indicating that the dissolution mechanism involved the breakdown of the passive layer and repassivation of the surface. Scanning electron microscopy (SEM) and white light interference microscopy (WLIM) were used to observe changes in morphology and roughness of the surface. The SEM images revealed the formation of pits with lacy covers at the surface during initial stages of the dissolution. At increased dissolution times, a transition from the lacy covered pits to open pits was observed. The images showed that preferential dissolution occurs on Ni layers grown at higher Ni(CO)4 decomposition temperatures. At longer dissolution times, the preferential dissolution also takes place at the boundaries between nickel laminae, which corresponds to the decomposition of Ni(CO)4 at different temperatures. Vale Canada and the Natural Sciences and Engineering Research Council (NSERC) of Canada.