Evaluation of the effectiveness of 3-mercapto-propyl-trimethoxy-silane and benzotriazole alkyl derivatives as bronze corrosion inhibitors

In the present work is investigated the behaviour of surface films formed by different bronze corrosion inhibitors as 3-mercapto-propyl-trimethoxy-silane and several benzotriazole alkyl derivatives. Some alkyl-derivatives of the 1,2,3-benzotriazole (BTA) as: 5-hexyl-1,2,3-benzotriazole; 5-dodecyl-1,2,3-benzotriazole and [5-(1-undecyl)dodecyl]-1,2,3-benzotriazole were synthesized in order to investigate the influence exerted by the aliphatic chain on the inhibiting properties of the base molecule (BTA). The protective efficiency of the organic coatings was determined by Thin Layer Activation (TLA) and gravimetric techniques on samples submitted to artificial weathering experiments (salt spray cabinet, cyclic wet dry tests and climatic chamber) and to outdoor exposures. For TLA measurements a ?-emitting radio nuclide 65Zn (t1/2= 244days), used as a corrosion tracer, was produced on the bronze surface by a high energy proton beam. At the end of the exposures tests, the radioactivity recovered on the bronze surface, once it was treated with a picking solution, allowed determination of the thickness loss. Results obtained in this study show that BTA molecules bearing long aliphatic chain act as the best corrosion inhibitors while 3-mercapto-propyl-trimethoxy-silane, despite an initial good performance, could eventually damage the bronze surface after long time exposures.