Characterization of Corrosion Mechanism in Copper Alloy Artefacts Buried in Soil from Haft Tappeh Ancient Site

The aim of this paper is identification of conditions of burial environment, corrosion events occurred in copper/bronze objects and characterization of relationship between soil environment and corrosion events in archaeological metals of Haft Tappeh site. For this purpose, 20 metal samples were selected from Haft Tappeh collection. The samples were observed and analyzed by optical microscopy, SEM-EDS and XRD methods. The different soil conditions were examined such as pH, physical nature and soluble salts. The results showed that the soil environment of Haft Tappeh is heavily corrosive and amount of soluble salts –especially chloride- are significant in soil. On the other hand, the copper/bronze samples are corroded heavily and in some cases, whole artefact has converted to corrosion products. The corrosion morphology and chemical nature of corrosion products in the copper/bronze samples showed that the main mechanism occurred in Haft Tappeh bronzes is active corrosion or “Bronze Disease”. Also, some events such as selective dissolution of copper, are obviously visible in these metal objects. Finally, the corrosion phenomena in Haft Tappeh samples are strongly related to corrosive nature of soil in this site.