EIS Corrosion Study of Co, Ni, CoNi, and CoNiMo Electrodeposited Thin Films

Abstract

Co, Ni, Co78Ni22 and Co75Ni22Mo3 magnetic thin films (5 micron) were electrodeposited galvanostatically from chloride baths containing sodium citrate as additive. These films were kept during 24 hours in a 5 wt. % NaCl solution (pH 6.4). During this period, OCP measurements and EIS were used to tail the corrosion of each film. The films were also analyzed by SEM before and after the corrosion experiments. The OCP of Ni, Co and CoNi decreased during the first seven hours of immersion, whilst for CoNiMo, it increased during the first eight hours due to the presence of a MoO2 layer below the film. In both cases, OCP remained constant thereafter. Different equivalent circuits were adjusted to the EIS data. From these circuits, charge transfer resistance and double layer capacitance of each film could be evaluated.