The study deals with the assessment of the atmospheric corrosion behaviour of Cu nanostructured thin films to investigate their corrosion susceptibility in comparison to bulk copper. Final goal is to evaluate the feasibility of employing Cu nanostructured thin films as reference material to assess the atmosphere aggressiveness in museum indoor environments [1].

Cu nanostructured thin films have been deposited on pure Cu sheets (30x30 mm, 0.45 mm thick) by plasma sputtering. The depositions have been performed in high vacuum conditions at the pressure of 1.3 x 10-2 mbar using Ar (purity 99.99%) as discharge gas and by applying an input power in the range of 100W to 500W for 20 minutes. The Cu film thickness was in the range of 100 nm to 300 nm.

A set of Cu nanostructured films have been submitted to accelerated aging test according to the ISO 3231:1993 standard method, in order to assess the resistance to humid atmosphere containing SO2. Samples have been maintained at 40oC for 8 hours in humid condensing atmosphere in the presence of SO2; then, the they have been dried at 23 ± 2o C and 50 ± 5 % RH for 16 hours. The aging cycle has been repeated for 3 days.

Eventually, a set of Cu nanostructured samples have been exposed in the museum of the Faculty of Archaeology, Sohag University, (Egypt) inside and outside five showcases to investigate the surface degradation as a function of the exposure time, from 1 to 12 months. The Cu nanostructured samples have been displayed close to some smart button sensors for temperature and relative humidity measurements to correlate their corrosion behavior with the microclimate conditions. Cu bulk specimens have been also exposed for comparison.

The accelerated aging test evidenced a mass increase from 0.1814 mg to 0.9222 mg after 24 and 72 hours, respectively, for the Cu nanostructured layer deposited at 100W. This layer is characterized by small Cu clusters of about 10-20 nm, as confirmed by the morphological characterization performed by scanning electron microscopy. This nanostructure leads to high surface reacted area and, therefore, to a higher corrosion susceptibility in comparison to the Cu films deposited at higher input power, which are characterized by big Cu clusters of about 30-50 nm.

Inside the museum, the temperature changes from 15°C during winter, to 35°C during the summer, while the RH increases during winter up to more than 50% and decreasing during summer down to 22%. Moreover, the humidity in the room changes up to 20% during the day, while in the showcases the change is much lower. However, the Cu nanostructured films exposed in indoor conditions, both outside and inside the showcases, show the formation of copper sulfides (chacocite Cu2S) and (covellite CuS) on the surface, as confirmed by EDS analysis, probably because of the presence of inappropriate materials used for the artefacts exhibition.