Corrosion Stability of Corrosion Products on an Archaeological Iron Artefact

A spearhead of archaeological and cultural significance has been found and analysed in Serbia. In the corrosion products of the artefact, the dominant phases were goethite (α-FeO(OH)) and magnetite (Fe3O4) whose presence explains a good preservation of the base metal, iron, over the centuries and the artefact stability after excavation. Besides goethite and magnetite, the corrosion products were identified to contain, to a lesser extent, less stable lepidocrocite (γ-FeO(OH)) and the phases that come from the rocks and soil from the surrounding environment (plagioclase). The phases containing chloride ions were not detected in the corrosion products (akaganéite, β-Fe8O8(OH)8Cl1.35), which indirectly indicates that the content of chloride ions was not significant in the underground exploitation conditions. The lack of chloride ions also contributed to the corrosion stability of the artefact during the period after excavation.