Patina nucleation on statuary bronze and brass

This paper focuses on the analysis of natural and artificial patina formation on statuary bronze and brass. Short term natural exposures of polished to 0.25μm samples were carried out in soft marine and urban atmospheres up to first corrosion nucleous formation. Laboratory simplest patina were also performed in an immersion-emersion CEBELCOR type equipment in distilled water during fixed spans of time. Also their artificial degradation by SO ₂ was simulated in the same equipment using urban synthetic rain water consisting on a 10 ^-4 M NaHSO ₃ solution as electrolyte. The structures formed during these different experimental conditions were observed in an environmental scanning electron microscope coupled to an energy dispersive X-ray analyser. Electrochemical characterisation of artificially weathered bronze and brass allowed clarifying the role of alloying elements on initiation as on the simplest patina formation processes as compared to pure copper as reference . They also contributed to a better understanding of the patina protectiveness degradation observed in atmospheres containing the most aggressive antropogenic pollutant. These results also justify the significant corrosion rate decrease determined at present on the latest Atmospheric Corrosion studies carried out in Europe as a consequence of the great effort devoted in the last decades to SO ₂ emissions control.