engleski

Protection of bronze patina by an environment friendly corrosion inhibitor

From antiquity bronzes have been widely used to produce sculptures and other objects of art. Bronze forms a thin layer of corrosion products, called patina, when exposed to atmosphere, soil or water. This patina is stable with time and protects the underlying metal, becoming a part of building or object it covers.1 Because of the increased air pollution (acid rain), patina that covers and protects bronze artifacts becomes more soluble. This is the reason why it has become necessary to protect the patina that covers bronze artifacts. In order to preserve metal works from the aggressive atmosphere, organic inhibitors are often required. Many inhibitors are toxic, so it has become a big concern to find new non-toxic inhibitors. Previous investigations2-4 have shown that imidazole derivatives are good copper corrosion inhibitors in different media. In this work the efficiency of a non-toxic organic inhibitor: 1-phenyl-4-methyl-imidazole, was examined on the Cu-6Sn bronze patina by the potentiodynamic methods and EIS, as well as by spectroscopic methods. In order of studying the patina protection it is necessary to obtain an artificial patina with a defined chemical composition similar to the patina formed spontaneously in urban atmosphere. To gain a composition characteristic for patina obtained in urban atmosphere it was formed potentiostatically in an aerated solution composed of 0.2 g L-1 Na2SO4 + 0.2 g L-1 NaHCO3 at pH 8.5 and 30°C. The SO42- ions are one of the main pollutants in urban atmosphere due to the industrial activity and the emission by automotive vehicles. The morphology and crystallographic structure of artificially obtained patina were examined with SEM, EDS analyses and Raman spectroscopy. The results have shown that the patina consists of a crystallic structure of malachite and a smooth structure of copper and tin oxides. The electrochemical measurements were made in the sulphate and carbonate solution, acidified to pH5 by addition of a dilute sulphuric acid, at room temperature. The results have shown that the studied environment friendly inhibitor efficiently protects Cu-6Sn bronze patina in sulphate-carbonate media.

bronze patina; corrosion inhibitors; acid rain

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