Protective silane treatment for patinated bronze exposed to simulated natural environments C. Chiavari a, e, * , A. Balbo b , E. Bernardi c , C. Martini d , M.C. Bignozzi e , M. Abbottoni b , C. Monticelli b a C.I.R.I. (Centro Interdipartimentale di Ricerca Industriale) Meccanica Avanzata e Materiali, Università di Bologna, Via Risorgimento 2, 40136 Bologna, Italy b Centro di Studi sulla Corrosione e Metallurgia “A. Daccò”, Università di Ferrara, Via Saragat, 4A, 44122 Ferrara, Italy c Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna, Via Risorgimento 4, 40136 Bologna, Italy d Dipartimento di Ingegneria Industriale, Università di Bologna, Via Risorgimento 4, 40136 Bologna, Italy e Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Università di Bologna, Via Terracini 28, 40131 Bologna, Italy highlights  Corrosion of outdoor bronzes in urban atmosphere.  Pre-patination by accelerated ageing tests in stagnant or runoff conditions.  Coating of the pre-patinated samples with 3-mercapto-propyl-trimethoxy-silane.  Characterisation of both coated surfaces and metal release after accelerated ageing tests.  Role of alloying metals in the corrosion/inhibition process by electrochemical measurements. article info Article history: Received 1 March 2013 Received in revised form 8 May 2013 Accepted 18 May 2013 Keywords: A. Alloys B. Coatings C. Electrochemical techniques C. Electron microscopy (SEM) D. Corrosion abstract The protective efficiency of 3-mercapto-propyl-trimethoxy-silane (PropS-SH) was evaluated towards bare and aged bronze. The wet & dry (stagnant rain) and dropping (runoff) techniques were used both for producing pre-patinated surfaces representative of real artefacts and for performing accelerated tests to verify PropS-SH protection efficiency. The surface corrosion products and the metal release were analyzed through spectroscopic techniques. The role of alloying metals in the corrosion/inhibition pro- cess was assessed through electrochemical analyses performed on bare and prefilmed alloying elements. The results showed good protective efficiency of the silane coating on bare and pre-patinated samples, both in stagnant and runoff conditions. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The introduction of effective, non-toxic protective treatments in the art conservation practice is increasingly demanded by Euro- pean health and safety regulations related to the use of chemical products [1]. As far as bronzes are concerned, a lot of different chemicals have been tested as corrosion inhibitors for outdoor corrosion [2e7]. Benzotriazole (BTA) and its derivatives are still the most commonly used compounds for this application, even if it is known that their efficiency is lower on bronze than on pure copper [6,8] and that there are toxicity and perhaps carcinogenicity con- cerns due to their leaching in the environment [9,10]. On the con- trary, the selection of corrosion inhibitors and coatings with high protective efficiency and low environmental impact is reputed essential. Even if copper is the main alloying element in bronze, it is well known that the corrosion behaviour of this alloy is quite different from that of pure copper. The corrosion process of this alloy is a complex phenomenon affected by both thermodynamic and kinetic factors [11]. Moreover, alloying elements induce microgalvanic ef- fects with consequent preferential dissolution of less noble metals, increase in the surface vacancies and non uniform corrosion attack. * Corresponding author. C.I.R.I. (Centro Interdipartimentale di Ricerca Industriale) Meccanica Avanzata e Materiali, Università di Bologna, Via Risorgimento 2, 40136 Bologna, Italy. Tel.: þ39 051 2090362. E-mail addresses: cristina.chiavari@unibo.it (C. Chiavari), andrea.balbo@unife.it (A. Balbo), elena.bernardi@unibo.it (E. Bernardi), carla.martini@unibo.it (C. Martini), maria.bignozzi@unibo.it (M.C. Bignozzi), marco.abbottoni@unife.it (M. Abbottoni), cecilia.monticelli@unife.it (C. Monticelli). Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys 0254-0584/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2013.05.050 Materials Chemistry and Physics 141 (2013) 502e511