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

The effect of carbon dioxide on the NaCl-induced atmospheric corrosion of copper was studied using in situ Fourier transform infrared microspectroscopy, in situ scanning Kelvin probe, and scanning electron microscopy/energy-dispersive analysis by X-ray. The copper surface was contaminated with a single NaCl particle and then exposed to relative humidity clean humidified air with two concentrations of ( and 350 ppm). After formation of an electrolyte droplet secondary spreading of electrolyte from the peripherical parts of the droplet was observed. The secondary spreading effect, which was much larger at than at 350 ppm, was a consequence of the formation of a galvanic element between a local cathode outside the edge of the droplet and an anode in the droplet. This lead to alkaline conditions in the secondary spreading area and transport of ions to the local cathode. The large secondary spreading at low concentration was possible due to lowering of the surface tension of the electrolyte/metal oxide interface at the peripheral parts of the droplet. Carbonate formation lowered the pH when the concentration was 350 ppm and resulted in a decrease of the pH and inhibition of the secondary spreading.