Corrosion analysis of the Tang Dynasty iron oxen at the Pujin Bridge Site, Shanxi Province

The Pujin Bridge Site in Shanxi is the first large-scale ancient ferry site along the Yellow River excavated in China. It has yielded a significant number of large-scale iron artifacts, represented by the iron oxen, constituting the largest known iron artifact assemblage of its period discovered globally to date. In recent years, corrosion pathologies such as corrosion flaking, exfoliation, and cracking have emerged and intensified on these iron objects, necessitating urgent research into their corrosion behavior and conservation. Representative spalled corrosion layer samples from the iron oxen surface were analyzed using modern analytical techniques to characterize the corrosion morphology and phase composition. The results indicate that the spalled layers have become completely mineralized with no residual metallic substrate remaining. The corrosion products comprise α-FeOOH, γ-FeOOH, Fe₃O₄, γ-Fe₂O₃, and β-FeOOH. Chloride ion enrichment is prevalent within the corrosion layers. A combination of the analysis results with meteorological monitoring data from the site reveals the impact of environmental factors on the corrosion process. This study constitutes a critical component of preliminary conservation research, providing a scientific reference for understanding the corrosion mechanisms of large-scale outdoor iron artifacts and formulating effective conservation strategies.