In Situ Studies of the Effect of SO[sub 2] on the Initial NaCl-Induced Atmospheric Corrosion of Copper

The initial -induced atmospheric corrosion of copper deposited with NaCl has been examined with Fourier transform infrared microspectroscopy under in situ and ex situ conditions in order to reveal the spatial distribution of reaction products. The oxidation of S(IV) turns out to be fast at the area of the NaCl-containing electrolyte droplet, and both sulfate and dithionate ions form. A copper-catalyzed reaction route for the sulfite oxidation has been suggested, which includes the formation of a Cu(II)–sulfito complex as an important step. The presence of gaseous oxidants such as and has previously been considered as an important prerequisite for the oxidation of sulfite on copper. The results obtained here suggest that the formation of local electrochemical cells induced by deposited NaCl particles could be another important route for S(IV) oxidation to sulfate formation. was found to promote the formation of less soluble paratacamite and nantokite (CuCl), which may slow down the atmospheric corrosion rate of copper.