Influence of commercial copper microstructure on the artificial green patina formation processes

Abstract

Commercial copper was submitted to a thermomechanical treatment in order to study its influence on the velocity of artificial green patina formation by immersion as well as on the thickness and adherence of the corrosion product formed on the underlying metal. The thermomechanical treatment enabled us to obtain samples with 9 to 60 μm grain size. These samples were submitted to an accelerated attack by immersion in an electrolytic bath in order to obtain a green patina. On the smallest grain size material it can be observed a patina with high thickness and adherence, smooth texture and homogeneous morphology. From the electrochemical assays it was established that the passivity current decreases for decreasing grain sizes. These results are consistent with the minimal porosity presented by the patina morphology which increase the protecting power. The underlying material did not present localized attack.