Macro-Micro-Mixed Galvanic Corrosion Behaviors of Pb Segregated Culture Relic Bronze

The macro-micro-mixed galvanic corrosion, which occurs on Pb segregated bronze relics, was investigated. The main corrosion products in a neutral chloride sulfate environment were Cu₂O, Cu₂(OH)₃Cl, PbSO₄ and Pb(OH)Cl. Pb particles in the substrate are considered to serve as "Cl-ion reservoirs" in the corrosion process. Exfoliation was observed only in samples with less Pb content and was highly related to the presence of unstable corrosion product Pb(OH)Cl, which also can disable the passivation phenomenon. A special passivation phenomenon caused by strong galvanic corrosion in the initial stage on the composite sample was observed. The DRT method was introduced to study the kinetics of corrosion reaction, and three distinct peaks were found in the τ ranges of 0.0149-0.1285, 0.6658-4.320, and 15.41-28.08 s, respectively. With the assistance of a quantum chemistry computation method, a mechanism was proposed to explain the special corrosion behaviors between Pb particles and substrate from a microscopic perspective.