Effect of oxide particle addition on the protectiveness of organosilane coatings on bronze exposed to synthetic acidic rain

The development of effective and environmentally acceptable protective coatings for the conservation of bronze artworks is still an unresolved issue. In recent years, silane coatings aroused great attention because some of them showed a good protection against bronze corrosion under conditions simulating outdoor exposures. This research, carried out within a M-ERA.NET project named B-IMPACT, aimed at evaluating the effect of the addition of nanoparticles (CeO2, TiO2, and La2O3) and micro-particles (fly ash) on the protective efficiency of 3-mercapto-propyl-trimethoxy-silane coatings applied on an alloy reproducing a Renaissance bronze. The protective efficiency of the coatings was monitored during 20 day exposures to tenfold concentrated synthetic acidic rain by electrochemical impedance spectroscopy. Bronze and silane coatings were characterized by scanning electron microscope coupled to an energy dispersive x-ray microprobe after exposure to aggressive solution. The results showed that these surface treatments offer very good protective efficiency, which was further improved by addition of CeO2 and, particularly, La2O3 and fly ash oxide particles, if a proper preparation protocol is adopted.