SEM and electrochemical characterization of bronze artifacts from the Francavilla archaeological site
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ORIGINAL PAPER
SEM and electrochemical characterization of bronze artifacts from the Francavilla archaeological site Daniela Imbardelli 1
&
Maria Caterina Gallucci 1 & G. Chidichimo 1
Received: 30 May 2016 / Accepted: 23 September 2016 # Springer-Verlag Berlin Heidelberg 2016
Abstract The excavations in the necropolis of the Francavilla Marittima archaeological area, in Calabria, have brought to light the rich burial artifacts and materials, dated between the end of the ninth and sixth centuries BCE. SEM/EDS analysis was conducted on some sections taken from a bronze artifact classifiable as an armilla or fibula fragment. Our aim was to elucidate the nature of the corrosion processes acting on the specimen. SEM investigation detected the segregation of tin towards the outer layer and a depletion of the copper content in the same region. Furthermore, the elemental distribution maps of the sections analyzed evidenced the presence of chloride ions in the border area between the corrosion patina and the metal alloy. Such anion migration of chloride ions into the interior of the alloy leads to a particular variant of the type of corrosion of structure that in the literature has been identified as structure I. A cavity electrode designed for electrochemical measurements of powders was used to perform cyclic voltammetry experiments devoted to explore the activity of the patina covering the surface of the bronze fragment. The surface layer consists mainly of tin and tin oxides; the layer immediately beneath it contains copper oxides. An increase of reactivity was shown in an acidic environment. The activity of the patina is greatly reduced at pH 5 and appears to be zero at neutral pH. Keywords Tin bronze . Bronze disease . SEM/EDS . Cyclic voltammetry . Corrosion mechanisms * Daniela Imbardelli [email protected]
1
Dipartimento di Chimica e Tecnologie Chimiche, CTC - Università della Calabria, Ponte Pietro Bucci, Cubo 15/D, 87036 Rende, CS, Italy
Introduction It is extremely difficult to find an answer to the question about what happens to a metal surface after being buried underground for many centuries, since the metal artifacts unearthed during excavations are often covered with shapeless and heavy oxide concretions. There is, however, a specific science, the so-called surface science, which is geared towards recovery of the original surface of the metal product, distinguishing it from the corrosion products (Bertholon 2001; Espi and Aucouturier 2001). The study of archaeological artifacts could bring new knowledge to the evolution of the processes of the corrosion of metal surfaces The corrosion mechanisms of archaeological metals are poorly understood because they are related both to the composition of metal alloys and to the nature of the burial environment, which vary depending on the geographic areas. For this reason, the knowledge about the corrosion mechanisms acting on ancient artifacts is very complicated, in spite of the significant impact that it can have in the field of archaeological studi
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