The use of scanning electrochemical microscopy for the characterisation of patinas on copper alloys

► SECM investigation on atmospheric corrosion of quaternary bronze. ► Characterisation of corrosion layer (patina). ► Patina has inhomogeneous electrochemical reactivity. ► Local in situ investigation of induced corrosion processes. ► Specific microstructural features cause different corrosion behaviours. The scanning electrochemical microscopy (SECM) was employed in the feedback mode for the visualisation of the local changes of morphology and reactivity, occurring on the surface of a quaternary copper-based alloy, due to exposure to environment. First, samples artificially aged by exposure to leaching acid rain were tested. The layer of corrosion products (“patina”) was investigated by performing SECM scans and approach curves, and the information provided by this electrochemical technique was compared with SEM–EDX–Raman characterisation. Successively, to highlight the early stages of localised corrosion processes, in situ examination of the surface exposed to an acidic environment was performed. The results show that SECM is a powerful characterisation tool of the deterioration process and is able to map the precursor sites of corrosion on the bronze surface.