Protective silane treatment for patinated bronze exposed to simulated natural environments

• Corrosion of outdoor bronzes in urban atmosphere.
• Pre-patination by accelerated ageing tests in stagnant or runoff conditions.
• Coating of the pre-patinated samples with 3-mercapto-propyl-trimethoxy-silane.
• Characterisation of both coated surfaces and metal release after accelerated ageing tests.
• Role of alloying metals in the corrosion/inhibition process by electrochemical measurements.

The protective efficiency of 3-mercapto-propyl-trimethoxy-silane (PropS-SH) was evaluated towards bare and aged bronze. The wet & dry (stagnant rain) and dropping (runoff) techniques were used both for producing pre-patinated surfaces representative of real artefacts and for performing accelerated tests to verify PropS-SH protection efficiency. The surface corrosion products and the metal release were analyzed through spectroscopic techniques. The role of alloying metals in the corrosion/inhibition process was assessed through electrochemical analyses performed on bare and prefilmed alloying elements. The results showed good protective efficiency of the silane coating on bare and pre-patinated samples, both in stagnant and runoff conditions.