Zinc photo-corrosion in neutral solutions

Abstract Photo-corrosion of zinc covered by an oxide layer in an oxygen atmosphere has been studied by polychromatic and laser illumination (λ=488 nm) in NaCl solution containing different amounts of dissolved oxygen. Corrosion acceleration by light occurs in the first stages of illumination, which was evident from both a positive photopotential shift as well as an increase in the cathodic limiting current. The acceleration effect disappeared in deoxygenated solution; therefore, it was ascribed to the photo-accelerated oxygen reduction. With illumination time the acceleration effect is replaced by photo-inhibition, which was evident from both impedance and mass-loss measurements. The inhibition effect was explained in terms of the light-assisted generation of a more protective layer on zinc. Photo-corrosion experiments by quartz crystal nanogravimetry did not supply evidence of photo-induced decomposition of the oxide layer during the initial corrosion stages.