engleski

Contribution of tin compounds to protective properties of patina layers on statuary bronzes

Outdoor bronze statues are usually exposed to aggressive environmental conditions thus covered with patina layers containing various constituents. Influence of sulfates is indicated as most important for creating patina layers under urban conditions. Majority of corrosion products in patina were identified as copper products but several studies have indicated the presence of tin compounds within naturally formed patinas on bronzes in atmospheric environments. In the present work, contribution of these tin-containing compounds to the protectiveness of a patina layer on statuary bronze (CuSn6) have been investigated. Artificial patina layers have been formed on bronze samples in 15mM Na2SO4 solution by immersion. The Cu/Sn ratio in patina layer was monitored versus immersion time using PIXE (proton induced X-ray emission) and the correlationbetween immersion time and Cu/Sn ratio was determined. The protective properties of patina layer have been determined by the method of electrochemical impedance spectroscopy. To avoid the contribution of increasing thickness of patina layer to corrosion resistance due to increased immersion time, the referent set of pure copper samples was immersed in the same solution as CuSn6 samples and measured at same time. These measurements helped establish correlation between protective properties of patina layer and Cu/Sn ratio in patina layer, and gain better understanding of bronze corrosion in neutral aqueous solutions.

bronze corrosion; patina; impedance spectroscopy

nije evidentirano