JOURNAL OF MATERIALS SCIENCE 38 (2 0 0 3 ) 407 – 411 Study on the inhibiting behavior of AMT on bronze in 5% citric acid solution LI YING ∗ State Key Laboratory of Corrosion and Protection, Institute of Metal Research, Academia Sinica, 62 Wencui Road, Shenyang 110015, People’s Republic of China E-mail: liying@icpm.syb.ac.cn FU HAITAO, ZHU YIFAN State Key Laboratory of Corrosion and Protection, Institute of Metal Research, Academia Sinica, 62 Wencui Road, Shenyang 110015, People’s Republic of China; Nanjing University of Chemical Technology, Nanjing, 210009, People’s Republic of China WEI WUJI Nanjing University of Chemical Technology, Nanjing, 210009, People’s Republic of China The corrosion behavior of bronze in the presence of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) has been investigated in 5% citric acid by electrochemical measurements such as potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS). It has been revealed that AMT is a good inhibitor for bronze. Both cathodic process and anodic process on bronze treated with AMT were different from that on the bronze without AMT treatment. Fourier transform infrared (FTIR) analysis was carried out to characterize the protective film, which revealed that the composition of the protective film was polymeric Cu(I)-inhibitor complex. AMT acted as bidentate ligand through the aminic nitrogen atom and the closed ring nitrogen in the complex. C  2003 Kluwer Academic Publishers 1. Introduction Corrosion of bronze artefacts is a serious problem for archaeologists, numismatists and archaeological chemists. Some corrosion products, such as CuO, Cu(OH) 2 · CuCO 3 , are useful for corrosion protection. But cuprous chloride, one of the corrosion products of artefacts, has no protection ability. For the bronze artefacts with this compound on their surfaces, the cor- rosion process is continued after excavation from early graves. Furthermore, this powdery corrosion product can be removed by wind. New corrosion processes will begin if this powdery product falls down on other un-corroded surfaces. This phenomenon is named bronze disease[1, 2]. Many attempts have been made to clean excavated bronze artefacts with different chemi- cal compounds, such as formic acid, alkaline glycerol, sulphuric acid and citric acid. However, these chemical compounds were unsatis- factory because they leached out some of the alloying metals during treatment. Moreover, corrosion products could not be removed completely. A few organic in- hibitors such as benzotriazole (BTA) have also been used to arrest corrosion by the protective layer com- posed of Cu-BTA polymeric complex. However, this complex covers the details of coins and artifacts. On the other hand, BTA can neither remove the powdery rust effectively nor replace chloride ions. ∗ Author to whom all correspondence should be addressed. Some researches showed that 2-amino-5-mercapto- 1,3,4-thiadiazole is an excellent inhibitor for copper and its alloys [3–7]. Ganorkar [8] revealed that AMT acts as an excellent remover for cuprous chloride pow- der. Furthermore, the inscriptions and other details of bronze cultural relics were very clear and visible after the treatment. Even though the scientists have found the promising use of AMT, the aspects of the inhibitive mechanism and characteristics of AMT towards the corrosion of bronze in the citric acid have not been studied efficiently and systematically yet. In this present work, the inhibit- ing ability, the inhibiting mechanism and the chemical component of the AMT protective film were investi- gated by the electrochemical method, FT-IR and STM. 2. Experimental method 2.1. Chemical and materials The Aggressive environment was an aqueous solution containing 5% citric acid (pH 2). The concentration of AMT was 7.5 mmol/L. AMT was produced by Nanjing Museum. Citric acid was analytical grade. Solutions were prepared using double distilled water. Bronze (Cu 87.4%, Sn 10.15%, Pb 2.36%, wt%) was employed as specimens. The specimens for potentio- dynamic and EIS measurement were covered by epoxy resin with 10 mm × 10 mm of working surface left. 0022–2461 C  2003 Kluwer Academic Publishers 407