Zinc photo-corrosion in neutral solutions

Photo-corrosion of zinc covered by an oxide layer in an oxygen atmosphere h as been studied by polychromatic and laser illumination (lambda = 488 nm) i n NaCl solution containing different amounts of dissolved oxygen. Corrosion acceleration by light occurs in the first stages of illumination. which wa s evident from both a positive photopotential shift as well as an increase in the cathodic limiting current. The acceleration effect disappeared in de oxygenated solution; therefore, it was ascribed to the photo-accelerated ox ygen reduction. With illumination time the acceleration effect is replaced by photo-inhibition, which was evident from both impedance and mass-loss me asurements. The inhibition effect was explained in terms of the light-assis ted generation of a more protective layer on zinc. Photo-corrosion experime nts by quartz crystal nanogravimetry did not supply evidence of photo-induc ed decomposition of the oxide layer during the initial corrosion stages. (C ) 2001 Elsevier Science Ltd. All rights reserved.