engleski

Artificially obtained sulphate-carbonate patina on bronze substrates – preparation and characterization

In the atmospheric corrosion condition bronze artefacts are gradually covering with patina. The color and composition of patina depend on concentration of aggressive compounds in the environment. In the presence of increased concentration of SO2 in the environment, sulphate patina occurs in form of brochantite (Cu4(SO4) (OH)6). Accordingly, in the presence of increased concentration CO2 in the environment, carbonate patina occurs in form of malachite (Cu2CO3(OH)2). Because the formation of patina is lengthy process artificial patination is using instead, according to recipes from literature. It is a common practice to artificially patinate the objects of art in order to form sulphide patina, which can be additionally treated to form an upper layer of sulphate or carbonate patina. Patina has an aestethic purpose but it should also provide corrosion protection to bronze substrate. In this work sulphate-carbonate patina is artificially formed on various bronzes (CuSn12, CuSn6, RG7). Pre-step is formation of sulphide patina using the potassium sulphide solution. Furthermore, sulphate-carbonate patina is formed both chemically and electrochemically. The samples are exposed to continuous immersion in simulated rainwater or accelerated aging performed in corrosion chamber. Electrochemical properties are examined by using electrochemical impedance spectroscopy (EIS). Composition and morphology of patina are examined by FTIR spectroscopy, SEM/EDX and optical microscopy. The influence of the substrate on the stability of patina is observed.

artificial patina ; bronze ; atmospheric corrosion ; impedance

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