Organosilane coatings applied on bronze: Influence of UV radiation and thermal cycles on the protectiveness

3-Mercapto-propyl-trimethoxy-silane (PropS-SH) coatings, with or without the addition of three typesof oxide particles (CeO2(nano-sized), TiO2(nano-sized) and La2O3(micro-sized)), were applied on qua-ternary bronze (Cu-Sn-Zn-Pb) and tested through natural and artificial exposures. In particular, uncoatedand coated samples were exposed both in the coastal town of Rimini (Italy) under sheltered/unshelteredconditions and in a climatic chamber where the samples underwent temperature/UV cycles, at constanthumidity. The sample surfaces were periodically characterized by SEM, EDS, micro-Raman, FTIR and XRDtechniques. Moreover, during natural exposures, runoff rainwater was collected monthly, in order toevaluate the release of the alloying metals from bronze by atomic absorption spectrometry (AAS). Theresults showed that micro-scale cracking and spalling phenomena took place during natural exposure,partly limiting the protective efficiency of the organosilane coating. In fact, UV radiation has a stronginfluence on coating performance, inducing structural modifications of the polymer. Oxide particle- andespecially TiO2-charged coatings proved to be more resistant to UV degradation.