Protective effect of a organosilane coatings on bronze exposed to concentrated synthetic acidic rain

Ancient and modern bronze artworks are an important part of our cultural heritage and the development of effective and environmentally safe protective treatments for their conservation is an important and still unresolved issue. Previous studies demonstrated that a silane coating based on 3-mercapto-propyl-trimethoxy-silane (PropS-SH) was very effective in protecting bronze from corrosion in environments that simulate outdoor exposure. Moreover, the addition of metal oxide nanoparticles (CeO2, TiO2, and La2O3) proved to be useful to improve silane crosslinking, thus increasing the coating protectiveness. This research aimed at evaluating the effect of the addition of Cu2O nanoparticles on the protective efficiency of PropS-SH and at evaluating the efficiency of Cu2O nanoparticles as corrosion inhibitor carrier when applied on pure copper and on an alloy reproducing a Renaissance bronze. The absorption of inhibitor on Cu2O nanoparticles was characterized by means of FTIR. Electrochemical tests (polarization curves and electrochemical impedance spectroscopy) were carried out on bare and coated specimens during 20 days of exposure to tenfold concentrated synthetic acid rain in order to monitor the corrosion processes and assess the efficiency of surface treatments. The results obtained from the different techniques revealed that Cu2O-charged coatings exhibited significantly improved corrosion protection of the substrate in comparison to plain silane coatings.