DOI: 10.1007/s00339-008-4451-0 Appl. Phys. A 92, 83–89 (2008) Materials Science & Processing Applied Physics A e. bernardi 1 c. chiavari 2, ✉ c. martini 2 l. morselli 1 The atmospheric corrosion of quaternary bronzes: An evaluation of the dissolution rate of the alloying elements 1 Dipartimento di Chimica Industriale, Università di Bologna, V. le Risorgimento 4, 40136 Bologna, Italy 2 Dip. Scienza dei Metalli, Elettrochimica e Tecniche Chimiche (SMETEC), Università di Bologna, V. le Risorgimento 4, 40136 Bologna, Italy Received: 5 September 2007/Accepted: 15 January 2008 Published online: 27 March 2008 • © Springer-Verlag 2008 ABSTRACT A comparative evaluation of the corrosion be- haviour of a G85 bronze in acid rain solutions was performed. As weathering technique, a wet–dry device was used to simu- late a cyclic exposure to stagnant rain. The weathering solutions were a collected natural rain and an artificial solution reproduc- ing the natural rain. The solutions were periodically monitored as concerns pH and metallic ion concentrations. On the aged specimens, surface studies were performed through OM, SEM and Raman analyses. At the end of weathering tests (40 days), weight loss measurements were carried out. The aim of this work was to examine the reproducibility in laboratory of the corrosive conditions determined by a natural acid rain. The final goal of this research is to investigate the dissolution of a quaternary alloy exposed to acid rains. The results showed slightly different corrosion behaviours as a consequence of the exposure to natural or synthetic rain. Concerning the mechanism of corrosion of G85 bronze, the in- novative approach adopted in this study allowed one to point out the contribution of each alloying element to the general corro- sion. Actually, while Cu and Pb progressively form insoluble corrosion compounds, Zn continuously dissolves, without form- ing detectable insoluble products. The absence of dissolved tin is remarkable. PACS 82.45.Bb; 82.33.Tb; 92.40.Ea 1 Introduction The corrosion behaviour of outdoor bronzes was the subject of many studies in the field of atmospheric corro- sion [1–9]. Up to now, accelerated corrosion tests have been per- formed in laboratories through the exposition of copper-based material to environments simulating the depositions of urban areas. Nevertheless, an artificial solution could hardly repro- duce the complexity of a real deposition. Then, with an inno- vative approach, a comparative investigation on the corrosion behaviour of the bronze exposed both to natural acid rains and ✉ Fax: +39-51-2093467, E-mail: cristina.chiavari@unibo.it to analogous synthetic rains has started to be performed [10]. The aim of this work was to examine the reproducibility in laboratory of the corrosive conditions determined by a natu- ral acid rain. The final goal of this research is to investigate the dissolution of a quaternary alloy exposed to natural acid rains. Actually, the use of natural rain as an ageing solution im- plies many complications related to the low volumes collected and to the low concentration of the pollutant components. In fact, the scarcity of volume is a limiting aspect for the selec- tion of the most appropriate weathering technique, that should require modest quantities of solution, possibly not to be re- newed. Moreover, the low concentration of pollutants in the real solutions can determine an extension of the time needed for the observation of corrosion phenomena, increasing the possibility of degradation of the solution itself. Considering all these points, we chose the wet–dry technique or alternate immersion as weathering method. In a preliminary study [10], a different behaviour was no- ticed between bronze specimens aged in natural rain and the ones aged in the analogous synthetic rain, not including the organic components. The necessity of considering organic compounds as factors influencing the dissolution behaviour of copper-based materials is perceived in literature [11–13]. In this work, in order to comprehend the causes of these discrepancies, a new comparison has been performed, be- tween the natural rain and the artificial one enriched of the main organic components (HCOO − , CH 3 COO − ) as well as of the aggressive inorganic components, H + , Cl − , NO − 3 , NH + 4 , SO 2− 4 . The wet–dry technique was used as a weathering method simulating exposure to a stagnant liquid (no run-off is con- sidered in this study, i.e., the specimens were cyclically im- mersed in the same weathering solution at each cycle). The two weathering solutions were monitored periodically, focus- ing on the changes of both pH and metallic ion concentrations. On the aged specimens, analyses were carried out in order to characterize the corrosion patina. Weight loss measure- ments were performed at the end of weathering tests. Whereas the weight loss measurements give information on the gen- eral corrosion processes, the determination of the metallic ion concentration in the solution allows the calculation of a disso- lution factor for each alloying component. By this method, the