Characterization of corrosion products on Han Dynasty iron swords excavated from Tuchengpo Cemetery in Wushan, Chongqing, China

Abstract Six iron sword samples dated to the Western Han to Xinmang period (206 BC–24 AD) of the Han Dynasty excavated from Tuchengpo Cemetery in Wushan, Chongqing, were characterized by Raman spectroscopy combined with SEM-EDS technology. The results showed that corrosion products on the iron swords were mainly divided into two corrosion layers. In the external layer, mineralized wood residue of scabbard was observed, and calcite, goethite, lepidocrocite, hematite, and carbon were detected. Different dense products were distinguished by color, including goethite (orange), lepidocrocite (reddish-brown), akaganeite (yellowish-brown), magnetite (black), and hematite (red), which formed rust sublayers in the internal layer. Chloride was mainly distributed in the internal layer, which had almost the same structure as the rust sublayers. This study provided the basic insights into the corrosion products of iron artifacts excavated from the Three Gorges region of Chongqing, as well as the comprehensive scientific information for protection of iron artifacts.