The use of experimental design for the study of the corrosion of bronze pretreated with AMT in artificial rainwater

Copper and copper alloys (bronze and brass) are usually employed in the manufacturing of cultural objects. When these alloys are exposed to the atmosphere, damaging corrosion products may form on their surfaces. Corrosion inhibitors are used to minimize the corrosion processes. However, the conditions that obtain the best anticorrosive performance of these inhibitors require the control of several chemical and operational parameters, which are, in practice, often chosen empirically. An experimental design was employed to determine the best values with respect to the concentration of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT), the ethanol content and the immersion time of bronze in the AMT solution to achieve the most protective films on the bronze surface. Electrochemical impedance spectroscopy assays of bronze samples with and without previous immersion in the inhibitor solution and exposed to artificial rainwater were performed at the open circuit potential. The parameters and the influence of their interactions on the inhibitory effect of the film formed on the bronze surface were shown to be statistically significant. The conditions for achieving the most protective films were 0.060 M AMT, 90% v/v EtOH, and 90 min of immersion.