Understanding the passivation layer formed by tolyltriazole on copper, bronze, and brass surfaces

Tolyltriazole (TTAH) is used industrially as a corrosion inhibitor for copper alloys, particularly in organic media. In this study, the morphology and chemistry of the layer formed by TTAH on copper and copper alloys under realistic conditions is investigated, with focus on the effects due to the presence of tin or zinc in the substrates. A combination of X-ray photoelectron spectroscopy (XPS), medium energy ion scattering (MEIS), and scanning transmission electron microscopy (STEM) has been used. It was found that an inhomogeneous metal–organic layer forms on the surface of copper specimens, likely in the form of copper nanoparticles surrounded by CuxTTAy complexes. This layer increases in thickness for at least 30 days. Chemically, the copper species in the layer are initially in the +2 oxidation state, but after longer exposure to TTAH, mostly Cu(I) is observed. In bronze samples, tin does not appear to segregate to the surface layer. In brass samples, zinc is depleted from the bulk and forms a thicker Zn_xTTA_y layer.