Atmospheric corrosion in the metal pool of Ali Qapu palace in Isfahan: an experimental study

Abstract

Isfahan, the capital of Iran during the Safavid period (1501–1736 CE), houses the Ali Qapu Palace. It was constructed during the Safavid period to be used as the royal court and a place for settling the affairs of the country. The palace was built in five stages; the final stage was the porch which contains a pool at its centre. The perimeter of the pool is made of white marble, the floor and walls are covered with metal sheets to which the marble is attached. Today, the dry pool is exposed to the urban environment of the metropolis of Isfahan. This study investigates the composition and the corrosion mechanism of the pool using optical microscopy, ICP-OES, SEM–EDS and X-ray diffraction techniques. The results show that the pool’s cover is made of a large number of sheets of copper joined together by copper and lead nails. The forging (cold-working and annealing) method was used to form the sheets. The corrosion products formed on the surface of the copper sheets are copper oxide and copper trihydroxychlorides. The mechanism of corrosion in the metal pool, including copper oxidation, is due to the formation of copper (II) compounds resulting from the reaction with Cl-contaminated airborne particulate matters (dust).