Corrosion components and mechanisms of the iron oxen of tang dynasty at Pujindu Site, Shanxi Province, China

The Tang Dynasty iron oxen (8th-century CE) at Pujindu Site, Shanxi, exhibit severe oxidative degradation from environmental weathering, with corrosion exfoliation compromising their aesthetic and structural integrity as archaeometallurgical artifacts. This study employed confocal Raman spectroscopy, SEM, and EDS to analyze three corrosion samples from the iron oxen group. The objectives were to characterize the compositional profiles of corrosion products and elucidate the corrosion-mineralization interplay. The results demonstrate that low-mineralization corrosion samples predominantly contain α-FeOOH (goethite), β-FeOOH (akaganéite), γ-FeOOH (lepidocrocite), and uncorroded ternary phosphide eutectic structures, with significant graphite aggregates observed within the rust layers. The distribution of β-FeOOH exhibits a certain correlation with that of chlorine (Cl), as expected given its chloride-incorporating nature. High-mineralization corrosion samples are dominated by α-FeOOH and Fe₂O₃ (hematite), where the Fe₂O₃ content decreases with increasing corrosion depth. The phosphorus eutectic structures (steadite) suggests that under alkaline conditions, steadite could form a passivation film, thereby halting further corrosion progression. The non-ferrous minerals are primarily composed of silica (SiO₂), albite (NaAlSi₃O₈), and calcite (CaCO₃), with silica predominantly distributed within highly mineralized porous rust layers and macroscopic fissures. Their formation mechanisms potentially reflect early-stage geochemical processes—specifically albitization, silicification, and calcification—during geological sedimentation. This study links casting defects in Pujindu Site iron oxen to corrosion product distribution, aiding corrosion assessment and conservation optimization.