The Use of Robinia Pseudoacania L Fruit Extract as a Natural Corrosion Inhibitor in the Protection of Historical Bronze Objects

Abstract

34 Background: The phenomenon of bronze disease is considered as the most important factor in 35 the destruction of bronze objects. Different methods have been proposed to deal with it. The 36 most important inhibitors used in this regard are BTA and AMT. While these inhibitors control 37 the corrosion, they are toxic and cancerous. In ideal conditions, these inhibitors are able to slow 38 down the activity of chlorine ion, but leave some side effects after a period of treatment. Today, 39 plant extracts are used for this purpose. In this study, Robinia pseudoacania L extract was 40 selected for this purpose. 41 Material and methods: The acacia fruit extract (200ppm to 1800 ppm) was used to the 42 prevention of corrosion inhibition of bronze alloy in corrosive sodium chloride solution 0.5 M. 43 The Bronze alloy used in this research, was made based on the same percentage as the ancient 44 alloys (Cu-10Sn). This alloy was used for the effect of corrosion inhibitors in the potentiostat 45 device, the weight loss method. The experiment was conducted in split plot desgin in time based 46 on the randomized complete design in four replications. 47 Results: Mean comparison showed that the highest rate of corrosion inhibition (93.5%) was 48 obtained at a concentration of 1800 ppm and with increasing the concentration of the extract, 49 corrosion inhibition also increased. EDX analysis of the control sample matrix showed that the 50 amount of chlorine, which is the most important factor in the destruction of bronze disease, was 51 8.47%wt while in the presence of corrosive sodium chloride solution, after 4 weeks, the amount 52 of chlorine detected was 3.20%wt. According to the morphology (needle and rhombus) of these 53 corrosion products based on the SEM image, it can be said that they are of the type of atacamite 54 and paratacamite that have caused bronze disease in historical bronze works. At higher 55 concentrations of acacia extract, the presence and growth of fungi has been observed, which 56 can cause poor performance of acacia extract in the long run. 57 Conclusion: the natural inhibitor of acacia fruit aqueous extract can play an effective role in 58 inhibiting corrosion of bronze, but at higher concentrations, it became fungal, which can reduce 59 the role of acacia fruit aqueous extract and even ineffective. Because natural inhibitors can play 60 an effective role in preventing the corrosion of bronze works. But to get better performance of 61 these inhibitors, more tests need to be done to improve and optimize. 62 63