Assessment of the interphase behaviour of two bronze alloys in archaeological soil

Abstract

The aim of this work is to evaluate the behaviour of bronze in archaeological soil by gravimetric study, electrochemical research and analytic survey. Archaeological soil samples were collected from Jama that date back to the second Punic war. Mineralogical, micro‐structural, micro‐morphological and chemical analyses of soil constituents were performed. The bronze samples correspond to Cu‐9.4Sn (B1) and Cu‐7.7Sn with 1% of Pb (B2). The open circuit potential value recorded for B2/corrosion product/soil is stable after only 7 min due to its reactivity allowing to a rapid development of a protective corrosion layer. The B2 interphase is more developed and stable than B1. Under anodic polarisation, the B2 alloy corrodes less than the B1 alloy owing to its lower anodic current. Based on the EIS study, two evolution stages of the bronze alloy/corrosion product/soil interphase are detected. For the first stage, the interphase is equivalent to two R//C loops at high and medium frequencies, respectively related to the corrosion layer and charge transfer process, associated to mass transport phenomena. For the second stage, the resistance of corrosion layer decreases and the first loop vanishes. SEM‐EDS analysis demonstrate that the first stage (20 days of immersion) can be characterized by a well covered surface with a thin corrosion product, the external layer exhibits low tin content. However, after 310 days of immersion, the surface state is different with isolated particulates composed by Cu and soil compounds on a cracked layer with the presence of craters showing an internal layer.

Tailored analytical strategies for the investigation of metallic artefacts from the Ayanis Fortress in Turkey

“…[3] In Table 1, the chemical-physical characterisation of the soil of the temple area of the Ayanis Fortress are listed for two locations: SOIL 0 collected around the artefact, Fig. 2(a) near the surface, and SOIL 6 collected around the artefact Fig.…”

Characterization of archaeological bronze and evaluation of the benzotriazole efficiency in alkali medium

“…Underneath the patina, the substrate bronze was submitted to a significant corrosion process at the grain boundaries leading to the formation of crevices. These crevices are open to the surface and a selective dissolution of copper may proceed [21,22].…”

Integrated analytical methodologies for the study of corrosion processes in archaeological bronzes

“…In corrosion patinas, lead reach values up to four times higher than the content in the bulk [3]. Tin enrichment instead, due to the solubility and high stability of tin species, is strictly connected to the decuprification process [7]. The migration processes of the elements or ions along the analysed thickness of the alloy create a concentration gradient through the corrosion layer.…”