The Protection Of Environmental Friendly Corrosion Inhibitors On Patinated Bronze

Bronze ware is a treasure in the palace of human civilization thanks to its high historical value, scientific value and artistic value. The surface of bronze wares is usually covered with various corrosion products, some of them are harmless to the substrate, but some others have a fatal threat to the substrate. In this paper, mainly via electrochemical methods, combined with composition characterization and surface analysis techniques, the effect of different surface corrosion products on bronze substrate has been studied, the protection effect of single corrosion inhibitor on different patinas has been tested, and environmental friendly corrosion inhibitors have been selected for two kinds of harmful patinas, CuCl and Cu2(OH)3Cl. The results showed that the corrosion rate of bronze covered with "harmful patina" was not necessarily greater than that of bare bronze, the corrosion rate of bronze covered with "harmless patina" was not necessarily less than that of bare bronze. The distinction between "harmful patina" and "harmless patina" was not based on whether the patina had a protective effect on bronze substrate, but whether the patina contained chlorine element. "Harmful patina" was certainly harmful, "harmless patina" might not be beneficial. A specific kind of inhibitor was only effective for specific patina, the inhibitor was not universal for all kinds of patinas. Therefore, different corrosion inhibitors should be selected for different patinas. For bronze covered with a CuCl patina, cysteine could adsorb chemically on CuCl patina and form self-assembled monolayer via sulfur atom in thiol and nitrogen atom in amino group. Cysteine could stabilize the patina layer and protect the bronze substrate effectively. When the concentration was 600mg/L, the inhibition efficiency could reach above 95%. For bronze covered with a Cu2(OH)3Cl patina, rare earth ion inhibitors, Ce2(SO4)3 and Ce(NO3)3, could form a deposition film on patina layer, optimize the porous structure of Cu2(OH)3Cl patina, improve the stability and density of the patina layer and enhance the protective effect of the patina layer on bronze substrate. When the concentration was 1000mg/L, the inhibition efficiency of these two rare earth ion inhibitors could both reach above 95%.