The effect of carbon dioxide ͑CO 2 ͒ 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 80 ± 2% relative humidity clean humidified air with two concentrations of CO 2 ͑Ͻ5 and 350 ppm͒. 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 Ͻ5 ppm CO 2 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 Na + ions to the local cathode. The large secondary spreading at low CO 2 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 CO 2 concentration was 350 ppm and resulted in a decrease of the pH and inhibition of the secondary spreading.

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The effect of carbon dioxide (CnormalO2) on sodium chloride (NaCl) induced atmospheric corrosion of copper was studied in laboratory exposures using microgravimetry, ion chromatography, Fourier transform infrared spectroscopy, and scanning electron microscopy with X-ray microanalysis. With lower amount of NaCl particles on the copper surface (<15μg∕cm2) , the corrosion rate was higher with <1ppm CnormalO2 than with 350ppm CnormalO2 , and for higher amount of NaCl (15μg∕cm2) , the corrosion was higher with 350ppm CnormalO2 . With lower amount of NaCl and low CnormalO2 concentration, a secondary spreading of electrolyte occurred from the droplets that formed at the particle clusters. This led to a larger effective cathodic area and a higher corrosion rate. However, at higher surface concentration of NaCl a spatial interaction effect between the local corrosion sites counteracted the increase in the corrosion rate due to overlap of the cathodic areas from the particles. Another factor, which influenced the corrosion process, was the effect of CnormalO2 on the pH of the surface electrolyte. Higher pH ( <1ppm CnormalO2 concentration) increased the formation of CuO, which improved the corrosion resistance of the corrosion product layer but hindered the formation of insoluble CuCl, whereby more soluble chloride ions were available for triggering localized corrosion and accelerating the initial atmospheric corrosion of copper. Hence, the overall influence of CnormalO2 and NaCl depends on at least three identified mechanisms.

Copper samples were exposed for 10 days in synthetic laboratory air at 75% relative humidity. To explore the possible influence of ozone on the atmospheric corrosion rate of copper, various combinations of the gaseous pollutants sulfur dioxide, nitrogen dioxide, and ozone were added. Ozone promotes the oxidation of sulfur dioxide to sulfate more efficiently than nitrogen dioxide does. A synergism between sulfur dioxide and ozone is suggested. This synergism includes both the oxidation of sulfur dioxide by ozone and the capability of ozone to form oxides, hydroxides, or other oxygen‐containing reaction products in the presence of smaller amounts of sulfur dioxide. The synergistic effect possibly can explain the unexpectedly high corrosion rates of copper found at rural sites within the UN ECE exposure program. The rural sites are characterized by low sulfur dioxide and nitrogen dioxide concentrations, and by high ozone concentrations.

The complexity of simulating indoor corrosion conditions has been elucidated by investigating a series of representative laboratory corrosion tests for electrical contact materials. The chemical composition of corrosion products formed during laboratory exposures of Cu substrates and Ni‐, Au‐ and Sn‐electroplated samples has been analyzed by x‐ray photoelectron spectroscopy and compared with results after field exposures in three telephone central offices. None of the evaluated laboratory tests is able to reproduce fully the corrosion products formed during actual field tests. The greatest similarities in chemical composition have been achieved in a laboratory atmosphere containing SO2 (0.25 ppm) and NO2 (1.8 ppm) which is able to produce several major phases also identified after field exposures in the telephone central offices. The results indicate that further improvement in similarities may be obtained by using a lower level of SO2 than was used in this work, and by introducing NH3 as a possible additional pollutant which may partly replace NO2 . The conclusions drawn from this work are restricted to environments similar to those found at present field sites.