Multiscale characterization of corrosion in archaeological artefacts from Motya (Sicily, Italy) through X-ray microscopy

Here we presented a multi-analytical approach (Multiscale X-ray Microscopy, Micro-Raman, SEM, HR- FESEM- EDS and EMPA) to explore corrosion mechanisms in different type of metal artefacts from Motya (Sicily, Italy) to gain the maximum information with the minimum sampling. Indeed, the elemental analysis provides key information on the role of alloying elements in production technology and corrosion process, whereas the structure information from Multiscale Xray Microscopy (XRM) enables multilength scale visualization of whole objects and provides the spatial distribution of corrosion phases. The results revealed the internal structure of the artefacts and the structural discontinuities which lead the corrosion, highlighting the compositional differences between the tip and the head of the iron nail (Bernabale et al., 2022). All copper-based artefacts were exposed to bronze disease corrosion induced by the presence of the reactive cuprous chloride (CuCl) located at the interface between external corrosion layers and the surviving metal core. In a Cu nail arsenic was forced outwards along inter-granular channels and it combined with Fe atoms at Cu grain boundaries, leading to the formation of copper-iron arsenate. Binary and ternary alloys revealed marked Cu and Sn selective corrosion and thicker patina compared with Cu metal due to the presence of Sn in chlorine-rich environment. The dissolution factor of copper in these alloys showed a great variability. In addition, the occurrence of cracks inside the bronze needle acted as new corrosion interfaces and involved the formation of complex and periodic stratified corrosion layers, leading to a complete mineralized structure (Bernabale et al. 2023).