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A carbon-containing layer is commonly found on copper patinas formed during laboratory chamber tests and field exposure.1)-3) The origin of this layer has been attributed to hydrocarbon contamination in the chamber of the surface analytical instrument,1) so its chemical composition has rarely been analyzed. Muller and McCrory-Joy reported that copper patinas formed on copper roofs at AT&T Bell Laboratories (40 years of exposure) included several monocarboxylic acids, alkanes, and polynuclear aromatic hydrocarbons, based on gas chromatography mass spectrometry.4) These compounds were extracted from the copper patina by using acetone. Muller and McCrory-Joy suggested that organic compounds possibly acted as an organic binder in the formation and growth of the copper patina and played an important role in its durability. Graedel et al. reported that atmospheric organic acids such as formic and acetic acid can corrode metals.5) For example, the so-called “bronze disease” is caused by acetic acid emission from wood shavings used as packing materials.5)-6) Notoya first demonstrated that localized corrosion in copper tubes occurs when the tubes are exposed to the formic acid vapor.7) The morphology of this corrosion has been described as an “ant nest.” Bastidas et al. showed that formic and acetic acid vapor corrode copper even at low concentrations and that the corrosion rate increases with the acid concentration.8)-9) Cuprite (Cu2O), copper hydroxide hydrate (Cu(OH)2・H2O), and amorphous copper formate (in the form of Cu(HCOO) or Cu(HCOO)2) form in formic acid vapor.8) In contrast, cuprite, copper acetate dihydrate (Cu(CH3COO)2・H2O), and copper hydroxide acetate (Cu4(OH)(CH3COO)7・2H2O) form in acetic acid vapor.9) In short, organic acids affect copper corrosion. A previous study showed that the corrosion products that form on copper exposed outdoors differ between summer and winter.10) Depth profiling analysis by Auger electron spectroscopy (AES) revealed that the carbon intensity at the surface of the copper exposed in winter was much stronger than that of the copper exposed in summer. The thickness of the carbon-containing layer formed in winter was much thicker than that of the one formed in summer. This thick layer cannot be explained by only the hydrocarbon contamination in the high vacuum analytical instrument. However, the chemical composition of this layer remained unclear. We have now focused on the carbon-containing layers on the surfaces of the copper patinas of the same samples as in the previous study and analyzed their chemical compositions using time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS is highly sensitive and does not damage the molecular structure of the surface. Notoya et al. used it to analyze benzotriazole (BTA) on copper; BTA is well known to inhibit corrosion on copper.11) However, as far as we know, there has been no reported TOFSIMS analysis of the carbon-containing layer formed on copper patina exposed outdoors. Zairyo-to-Kankyo, 55, 146-151(2006)

Surface Analysis of Copper Patinas Formed Outdoors by using Time-of-flight Secondary Ion Mass Spectrometry