Spontaneous growth of silver metal whiskers in burial-induced corrosion: a synergistic multi-disciplinary approach to address complexity

Metal whiskering remains a significant challenge for the scientific community, as the fundamental physics underlying whisker formation is still poorly understood. This study reports the first identification of silver metal whiskering developed in burial conditions, revealing intricate silver microstructures with nanoscale features. Moreover, it introduces an innovative methodology based on micro-X-ray Fluorescence (µXRF) for the rapid screening of whiskering over large sample collections. The whiskers were detected and characterised by performing a tailored multi-analytical, minimally invasive strategy, starting from Scanning Photoelectron Microscopy (SPEM) over the surface of an ancient Roman coin that has undergone centuries of natural ageing in soil. The physico-chemical properties of these whiskers were then investigated with a combination of X-ray Photoelectron Spectroscopy (XPS), Focused Ion Beam (FIB), and Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS), to determine their metallic state and their origin. The experimental results confirmed the assignment of the observed phenomenon to metal whiskering. The investigation additionally uncovered a complex influence of whiskers' presence on the surface conductivity of the sample, characterised by a domain structure. The present work deepens the knowledge on metal whiskering, making a step towards its full scientific understanding, with significant implications for industrial applications and cultural heritage studies.