Influence of nanoparticles on the inhibiting efficiency of organosilane coatings on bronze. Part 1: Electrochemical characterization

The development of effective and environmentally acceptable corrosion inhibitors for the conservation of bronze and gilded bronze artworks is an important and still open issue. In this field, most studies are focused on the use of benzotriazole or its derivatives but, in spite of their high efficiency in the corrosion protection of pure copper, these compounds are not very effective when applied on bronze, besides being toxic for the environment and the living organisms. In the recent years the “green” silane coatings aroused great attention as a promising alternatives to conventional chromating. This class of organic coatings showed a good protection against corrosion of many different alloys, depending on the moiety of the silane molecules. This work is part of a wider project concerning the conservation of bronze and gilded bronzes. It aims at evaluating the protective efficiency of a silane (3-mercapto-propyl-trimethoxy-silane), in the absence and in the presence of some oxide nanoparticles (CeO2, TiO2, CeO2ZrO2 and La2O3), towards the corrosion of an alloy reproducing the composition and microstructure of a Renaissance bronze. The tests on the silane coatings consisted in monitoring the corrosion process by Electrochemical Impedance Spectroscopy during 20 days exposures to 3.5% NaCl solution and in recording the polarization curves at specific immersion times. The results showed that these surface treatments offer an excellent protective properties if a proper curing time at room temperature is waited. The addition of CeO2, La2O3 and TiO2 nanoparticles permits to short down the curing time, while keeping the coating protectiveness.