Appl Phys A (2013) 113:923–931 DOI 10.1007/s00339-013-7719-y Evaluation of the inhibitive effect of benzotriazole on archeological bronze in acidic medium Hèla Hassairi · Latifa Bousselmi · Slim Khosrof · Ezzeddine Triki Received: 14 April 2013 / Accepted: 19 April 2013 / Published online: 4 May 2013 © Springer-Verlag Berlin Heidelberg 2013 Abstract An archaeological bronze artefact was a Punic coin excavated from the north east of Tunisia in 2001. The composition of the copper alloy revealed a content of 3.5 % of tin and 1.4 % of lead with the presence of some sulphur heterogeneity. The surface presents some rough- nesses and cracks and is covered by a corrosion layer of 20–40 μm thickness. The use of benzotriazole (BTA) as an inhibitor has become a standard element for the preserva- tion of cuprous-based metals. In order to investigate the be- haviour of BTA in an acidic medium, an Electrochemical Impedance Spectroscopy (EIS) investigation was performed to characterize the electrochemical behaviour of the inter- face of the archaeological bronze sample/acidic medium without and with BTA addition. Impedance diagrams ob- tained at different immersion times show that the presence of the inhibitor prevents the diffusional process observed in the absence of BTA. The inhibition of the pre-polarized bronze surface revealed that the mechanism of action of the benzo- triazole molecule in an acidic medium is governed by the chemisorption process. H. Hassairi · E. Triki Unité de Recherche ‘Corrosion et Protection des Métalliques’, Ecole Nationale d’Ingénieurs de Tunis, 1002 Tunis, Tunisia H. Hassairi · L. Bousselmi ( ) Laboratoire de Traitement des Eaux Usées, Centre de Recherche et des Technologies des Eaux, Route Touristique de Soliman, 8020 Soliman, Tunisia e-mail: latifa.bousselmi@certe.rnrt.tn Fax: +216-79-325802 S. Khosrof Institut National du Patrimoine Tunisie, 04, Place du Château, 1008 Tunis, Tunisia 1 Introduction In principle, archaeological relics should be kept as they were found, and untouched in any way. However, some ob- jects will need to undergo preservation treatments to prevent the possibility of further oxidation that might cause them to deteriorate. Damaged artefacts must be restored to their original form for research, storage or exhibition. Bronze ob- jects are especially fragile, as they undergo the process of oxidation while buried. Their deterioration continues rapidly after excavation. Therefore, they must undergo an efficient treatment for their preservation. The identification of the corrosion products is not only an essential requisite for selecting the cleaning procedure in conservative and restorative treatments for preservation of our cultural heritage, but also an interesting tool to clar- ify the morphological corrosion phenomena occurring on a bronze surface when it is exposed to different corrosive me- dia [1, 2]. Various investigations have shown that the corrosion lay- ers on these artefacts are the result of an interaction of the alloy with the buried context. The main constituents of the surface layer of the patina are green-coloured copper II com- pounds covering a red cuprous oxide layer in contact with the metal core of the alloy [3]. At the present time, the use of benzotriazole (BTA) has become a standard element for the preservation of cuprous- based metals [4]. Many efforts have been made to elucidate the mechanism of action of BTA and the mode of fixation of the molecule at the copper (oxide) surface. The treatment with BTA does not remove the cuprous chloride from the artefact; rather, it forms a barrier between the cuprous chlo- ride and moisture of the atmosphere [5]. In this method of protection, the benzotriazole forms an insoluble, complex compound with cupric ions. The development of this in- soluble complex over the cuprous chloride forms a barrier