Preliminary Study on the Role of Humic Substances in the Early Corrosion Behavior of High-Tin Bronze Alloys Under Simulated Soil Conditions

To investigate the influence of humus on the corrosion behavior of high-tin bronze in soil environments, potentiostatic polarization was applied to simulate early-stage corrosion under controlled conditions. Open-circuit potential and potentiodynamic polarization tests were performed, and corrosion products were characterized by stereo microscopy, SEM-EDS, and confocal Raman spectroscopy. A Cu–Sn–Pb ternary alloy was examined in simulated archaeological soil solutions with selective humus addition at different pH values. A bilayer structure, consisting of a secondary corrosion layer and a semi-corroded transition zone, developed in all media, with more extensive corrosion under weakly acidic conditions. In acidic environments, humus enhanced preferential α-phase corrosion, associated with copper depletion and tin enrichment as SnO₂. Under weakly alkaline conditions, humus mainly affected surface color and micro-morphology without altering the overall corrosion pattern. Electrochemical testing reproduced corrosion layer structures similar to those formed during early burials, but differences in morphology were observed. The results suggest that, as an accelerated corrosion technique, electrochemical methods can reproduce key features of early-stage corrosion in high-tin bronze and serve as an effective tool for monitoring corrosion behavior.