An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment.

Dajana Mikić,Neven Peko,Helena Otmačić Ćurković,Tadeja Kosec

doi:10.3390/ma14082063

Abstract

Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H2S and SO2 in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy.

Highlights

IntroductionBronze has been used from ancient times for decorative and artistic objects
The variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas
The patina and bronze surface were analyzed by X-ray fluorescence (XRF), EDS, Raman, and FTIR analysis

Summary

Introduction

Bronze has been used from ancient times for decorative and artistic objects. Even though bronze is known to be a relatively corrosion-resistant alloy, a significant decay, in terms of surface recession and loss of details in artefacts, has been observed on bronze objects exposed outdoors. Copper and its alloys spontaneously form a thin layer of brownred oxide, cuprite Cu2 O. The secondary corrosion products form that might change the color from dark brown to greenish tones due to the formation of various sulphate, chloride, or carbonate copper species [1,2,3]. Polluted urban environment enhances the dissolution of patina and underlying bronze material. The rate of patina dissolution depends on its composition and morphology as well as on the environment corrosivity

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