Advanced Laboratory Study on the Atmospheric Corrosion of Zinc under Thin Electrolyte Layers

The corrosion rate of zinc under thin electrolyte layers and during exposure to wet/dry cyclic conditions has been investigated in sodium chloride (NaCl) and ammonium sulfate ([NH4]2SO4) solutions using electrochemical impedance spectroscopy (EIS) and potential measurements. The integral corrosion rate was found to decrease with successive cycles, thereby demonstrating that the formed corrosion products confers protection to the zinc surface. The corrosion product formed in (NH4)2SO4 solution was less corrosive than that formed in NaCl solution. Corrosion rates were greatly accelerated under thin electrolyte layers of thicknesses 1 μm to 90 μm, as a result of the decrease of the diffusion layer thickness that led to a higher rate of oxygen reduction. The corrosion rate of zinc was independent of electrolyte thickness >650 μm. The effect of sulfur dioxide (SO2) gas on the corrosion rate of zinc under different thin electrolyte layers was studied. The corrosion mechanism of zinc under thin electrolyte layers is suggested.