The Initial Stages Of Zinc Atmospheric Corrosion In The Presence Of Chloride

THE INITIAL stages of zinc atmospheric corrosion have been studied using ex situ I electrochemical-impedance spectroscopy (EIS) in a non-aqueous electrolyte (methanol). Compared with the traditional techniques in the study of atmospheric corrosion, such as gravimetry, the EIS technique greatly shortens the exposure time for the detectable corrosion to a few hours at any relative humidity. This work investigated the critical environmental conditions, such as relative humidity, contaminated salt surface concentration, etc., for the corrosion product formation in the presence of chloride. The samples were exposed to synthetic atmospheres with the careful control of CO2 and O-2 concentrations, relative humidity, temperature, and contaminated salts. The corrosion products were analysed quantitatively by EIS for polarization resistance (R-p) and qualitatively by grazing-angle XRD and FTIR. Zinc hydroxy carbonate and zinc oxide were found responsible for the protectiveness of this surface layer against contaminated chlorides.