Electrochemical Impedance Spectroscopy Study of the Corrosion Process on Coated Galvanized Steel in a Salt Spray Fog Chamber Available to Purchase

The behavior of three different paint systems was investigated using the electrochemical impedance spectroscopy (EIS) technique. The coatings, based on chlorinated rubber, alkyd resin, and waterborne acrylic resin, were applied on galvanized steel and exposed in a salt spray fog chamber (SSFC) according to ASTM B117. The evolution of the impedance spectra over exposure time allowed a comparison to be made among the barrier properties of the three tested paints. In all cases, the number of time constants in the impedance spectra increased with exposure time, which was related to the development of different processes at the metal/coating interface. The accumulation of zinc corrosion products at the zinc/coating interface and/or oxygen diffusion throughout those deposits and the paint film were considered the physical phenomena responsible for the observed time constants. The corrosion products were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and x-ray diffraction (XRD) techniques. The main corrosion product characterized was simonkolleite, Zn₅(OH)₈Cl₂·H₂O.