Novel insight into bronze disease gained by synchrotron-based photoelectron spectro-microscopy, in support of electrochemical treatment strategies

A recent assessment (Giovannelli, G., D'Urzo, L., Maggiulli, G., Natali, S., Pagliara, C., Sgura, I. & Bozzini, B. 2010. Journal of Solid State Electrochemistry, 14: 479–94.) of the corrosion state of a late Bronze Age artefact (ca. 1100 BCE) exposed to a coastal environment, based on optical and scanning electron microscopies, X-ray fluorescence mapping, and X-ray diffractometry, led to recognition of bronze disease conditions essentially related to the presence of nantokite locked inside mesoscopic subsurface pits. The object was then treated successfully with a novel electrochemical approach specifically designed to allow penetration of the electric field into deep, screened pits. In order to further develop and optimize this promising approach by fine-tuning the capabilities of electrochemical control, more insight is required on the specific morphochemistry of the corrosion product scenario. To this end, here we report a space-dependent compositional and chemical-state analysis, performed with synchrotron-based scanning photoelectron microspectroscopy. The investigated object consists of a segregated cast bronze. The prevailing corrosion form is preferential attack of Sn-rich phases, accompanied by a synergistic type of Sn and Cu attack triggered by the peculiar type of decuprification taking place in a bronze disease framework and characterized by the formation of Sn(OH)Cl as a result of local HCl generation in the Cu corrosion process.