The corrosion characteristics and electrochemical conservation treatment for an archaeological lead ossuary from Jordan

Abstract

This study investigates the composition and corrosion of a lead ossuary excavated from the archaeological cemetery located on the site of the Queen Alia International Airport, Jordan. It also presents its conservation treatment using the potentiostatic reduction method. X-ray fluorescence (XRF) and scanning electron microscopy/ energy dispersive X–ray spectroscopy (SEM/EDX) analyses showed that the ossuary was made from a relatively pure lead metal. Examination of the corrosion products using X–ray diffraction (XRD) and SEM/EDX analyses indicated the presence oxides, carbonates and chlorides of lead as the main corrosion products on the ossuary. The metallographic examination showed a cast α-Pb dendritic microstructure. A linear sweep voltammetry (LSV) scan for a small fragment from the ossuary in a sodium sulfate solution allowed identifying the working conditions to reduce the corrosion products to lead metal. Chronoamperometry (CA) techniques helped to monitor the reduction process and determine its completion. The potentiostatic methods showed an excellent effectiveness in determining treatment parameters and monitoring the reduction process of the corrosion products on the ossuary and to prevent over-treatment. The reduced ossuary was finally coated with Paraloid B72 to prevent corrosion reoccurrence in the poor environmental conditions of the storage area.