Chloride Gradient Corrosion Characteristics of Large Outdoor Iron Column Artifacts at the Pujindu Site, China

Large outdoor iron artifacts are vulnerable to environmental factors, and their conservation presents an enormous challenge. The Pujindu site is renowned for its large iron artifacts. The ‘Qixing Column’ iron columnar artifacts exhibit gradient corrosion from top to bottom, which may compromise their stability. In this study, the corrosion characteristics of iron columns and the soluble chlorine content in their environmental samples were analyzed using scanning electron microscopy-energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, and ion chromatography. Elemental chlorine caused structural differences in the corrosion layer at various locations on the iron column. Furthermore, from the top to bottom of the iron column, the soluble chlorine content increased, leading to a deterioration in the stability of the corrosion layer. Groundwater was identified as the primary source of chloride contamination in the iron artifacts at the site through the analysis of environmental data. This investigation elucidates the gradient corrosion characteristics of large iron objects by chloride ions, underscores the critical role of groundwater in the deterioration of outdoor iron artifacts, and provides valuable insights for the development of targeted conservation strategies.