A Multi-Analytical Study on Characteristics and Formation Mechanisms of Corrosion on Bronze Sheets from the Chu Culture Tombs in Dangyang, China

Bronze sheets from the Spring and Autumn periods (approximately fifth century BCE), which were excavated from Chu culture tombs located in Dangyang, Hubei Province, China, were analyzed in this study. The objective was to explore and elucidate the correlation between the alloy composition, corrosion products, and the surrounding burial environment, while also offering insights into the underlying corrosion mechanisms. A combination of techniques including optical microscopy (OM), SEM–EDX, XRD, micro-Raman spectroscopy, and ion chromatography (IC) were employed to examine these samples. The analysis revealed that the bronze sheets consisted primarily of Cu-Sn-Pb alloys. Metallographic examination showed that the artifacts were initially hot forged and later subjected to partial cold working; some of the samples exhibited sulfide inclusions. XRD and Raman spectroscopy results indicated that the primary corrosion products were SnO₂, copper sulfates, and various copper sulfides. Additionally, CuO was identified. Raman spectra of the black-gray corrosion products showed two broad peaks at approximately 1360 and 1580 cm⁻¹. Further analysis of the Raman parameters suggested the presence of soot or humic substances. Based on these findings, it was hypothesized that the sulfide inclusions within the metal's microstructure, the presence of SO42−, and the activity of sulfate-reducing bacteria in the surrounding soil, combined with the sealed and anaerobic conditions of the tomb, could account for the observed sulfide corrosion products on the bronze artifacts. Moreover, the detection of tenorite and soot points to the possibility that the tombs experienced a fire during the burial process.