Thiadiazole derivatives as inhibitors for acidic media corrosion of artificially patinated bronze

Electrochemical impedance spectroscopy (EIS) and SEM‐EDX observations were used to evaluate the inhibiting effect of four thiadiazole derivatives, i.e. 2‐mercapto‐5‐amino‐1,3,4‐thiadiazole (MAT), 2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole (MMeT), 2‐mercapto‐5‐acetylamino‐1,3,4‐thiadiazole (MAcAT) and 2‐mercapto‐5‐phenylamino‐1,3,4‐thiadiazole(MPhAT) on the corrosion of naked and artificially patinated bronze surface exposed to an acidic solution (pH 3) that simulates a strongly polluted rainfall. For comparison reasons, the inhibiting effect of benzotriazole (BTA) was also examined. In an attempt to better understand the influence of solution pH on the adsorption of the thiadiazole derivatives and to correlate their structural and electronic characteristics with the experimental inhibition efficiencies, quantum chemical calculations were performed starting with thiadiazole and its protonated derivatives. Finally, a possible inhibition mechanism of the thiadiazole protonated species on bronze corrosion was proposed. It was concluded that MMeT and MAT allow the stabilization of the patina layer, leading to the protection of the bronze substrate and their effectiveness significantly increase with the immersion time.