Comparative Study of the Corrosive Behaviors of Rust Layers on Bronze Ware in Different Corrosive Environments

It is of great significance to clarify the corrosion mechanism of rust layers on bronze ware for appropriate conservation measures. In this study, the corrosion behavior of Cu-Sn bronze alloys in a 3.5 wt.% NaCl solution and a simulated archaeological soil solution was studied and compared using electrochemical measurements, microscopic observations, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the presence of Cl^- was the key factor leading to the formation of harmful rust such as Cu₂(OH)Cl₃. In the NaCl solution, the rapid accumulation of Cl-containing corrosion products provided a certain degree of protection to Cu-Sn alloys, but the products easily fell off, thus increasing the continuous corrosion reactions again. This resulted in a significant increase in the corrosion rate of the alloy (i_corr from 4.845 μA·cm^-2 to 27.21 μA·cm^-2) and a decrease in polarization resistance (R_p from 5.17 kΩ·cm² to 3.27 kΩ·cm²). In contrast, the corrosion reactions of the Cu-Sn alloy were dominated by complex ions other than Cl^- in archaeological soil environments, and the corrosion products tended to form stable and dense rust layers (i_corr was always lower than 1.6 μA·cm^-2, and R_p was maintained above 24 kΩ·cm²), which improved corrosion resistance by two orders of magnitude compared to the unstable rust layer that formed in NaCl solution. In addition, Cl-containing corrosion products boosted the wettability of rust layers, thereby facilitating penetration of corrosive media that strengthened corrosion reactions. This study deepens our understanding of the degradation mechanisms of bronze artifacts and provides a scientific basis for developing bronze conservation strategies.