Interference by cerium cations during the multi-step zinc dissolution process in a chloride-containing electrolyte

The influence of cerium ions in the dissolution mechanism of zinc has been evaluated by means of electrochemical impedance spectroscopy in a sodium chloride media. The multi-step dissolution process of zinc is modified during the early stages of immersion. The initial chloride ions adsorption on the surface is hindered by the adsorption of cerium ions which act as a precursor of the rich cerium layer formed with time. This was revealed by the appearance of two constant times at high and intermediate frequencies related to the charge transfer resistance and the adsorption process. At longer times, 24 h, the second arc evolves toward a diffusion tail. As time increases the behaviour of the galvanised steel depends on the Ce concentration. For 500 and 1000 ppm CeCl3 · 7H2O there was no evidence of the constant time associated to the porous corrosion products of zinc at the high frequency range.