Mechanism of incipient annular corrosion of high-tin bronze in simulated soil solution.

This article investigates the initial corrosion mechanism of Cu–Sn–Pb bronze alloy (18.2 wt-% Sn) in a simulated soil solution, focusing on the roles of chloride ions (Cl⁻) and the alloy's microstructure. Using techniques such as optical microscopy, scanning electron microscopy, scanning Kelvin probe (SKP), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods, the study finds that the copper-rich α-phase exhibits a more negative corrosion potential and is the primary site of early corrosion, particularly in an annular region linked to tin content variations caused by dendritic segregation. Chloride ions do not directly participate in the initial corrosion but damage the copper oxide layer, promoting copper dissolution and subsequent accumulation of tin oxides on the surface. Lead particles oxidize to lead carbonate in the presence of bicarbonate ions, while sulfate and nitrate ions show minimal involvement in early corrosion stages.