THE INFLUENCE OF A THIN ELECTROLYTE LAYER ON THE CORROSION PROCESS OF ZINC IN CHLORIDE-CONTAINING SOLUTIONS

The corrosion of zinc in a neutral chloride solution was investigated under a thin electrolyte layer by both electrochemical (complex impedance) and spectroscopic (FTIR and RAMAN) techniques. It was established that confinement of a thin electrolyte layer on top of the corroding zinc sample leads to a specific impedance distribution obeying the transmission line model of a porous electrode. After correcting for this effect, increase of the charge transfer resistance and shift of the corrosion potential in the cathodic direction are consistent with oxygen depletion when the layer thickness is reduced. Corrosion products are identified by comparison to FTIR spectra of reference compounds: zinc hydroxychloride, zinc hydroxycarbonate and zinc oxide. In agreement with the chemistry changes shown by the impedance data. confinement of the corroding area is found to promote the formation of hydroxycarbonate while only hydroxychloride is detected during corrosion in bulk conditions. No chloride-containing products are detected with thicknesses below 1 mm. In situ RAMAN spectra performed across the thin layer and a glass window confirmed totally these conclusions.