engleski

Protection of bronze covered with patina by innoxious organic substances

Archaeological or cultural bronze artefacts are exposed in indoor or in outdoor. They often suffer of a substantial alteration due to a increasing atmospheric pollution. It becomes, therefore, necessary to protect them efficiently together with patina layer. The use of clear-coating or wax with some corrosion inhibitors such benzotriazole are largely employed in museum, but they modify the visual aspects and also the inhibitors employed are often noxious or even toxic. In this work, we propose use of some innoxious compounds to use as corrosion inhibitor of bronze artefacts covered with patina. The bronze used was Cu-5Sn. This composition was selected after a preliminary work on several archaeological bronzes found in Transylvania, Romania, dated of Neolithic period. First, the patina was formed on this bronze, under potential regulation, in NaHCO3+Na2SO4, pH 8, solution during three days. A light blue patina was obtained. These specimens were then dipped into an aqueous solution of various organic compounds during three hours. The organic compounds examined were 1mM methyl-tolyl-imidazole, 5mM 1-phenyl 4-methyl-imidazole, 0.1mM 2-mercapto-5-R-amino-1, 3, 4-thiadiazole, and for comparison benzo-triazole. The corrosion behaviour was examined in the same solution to the patina formation, but pH of which was adjusted to 5 by addition of H2SO4.The impedance spectra collected showed, all of them, three depressed capacitive loops. On the bases of these capacitance values, these loops were allocated to the surface film with ionic conduction, the double layer capacitance with the charge transfer resistance, and the oxidation – reduction process involving the surface patina. The protective effectiveness determined from the resistances increased with the immersion period. The authors gratefully acknowledge the EGIDE to financial support of this project under the licence number EcoNet 10 279NA.

Copper-Tin bronze; Imidazole; Thiadiazole; Raman spectroscopy; Corrosion

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