Exploring environmentally friendly localised corrosion inhibitors through local electrochemical measurements using multielectrode arrays

Localised corrosion is the result of complex heterogeneous electrochemical processes occurring on metal surfaces. Localised corrosion control is one of the most difficult issues in corrosion science and engineering. This study reports a new approach to exploring effective and environmentally friendly localised corrosion inhibitors through local electrochemical measurements using multielectrode array probes. Local galvanic current, local polarisation, and local electrochemical impedance spectroscopy (EIS) measurements were performed on an electrode array probe exposed to waterline corrosion conditions, with and without the presence of rare earth metal (REM) inhibitors that are known to be effective for inhibiting general corrosion. The results revealed significant differences in the behaviour of two REM inhibitors, with La(4OHcin)₃.5H₂O exacerbating localised corrosion by generating intense anodic sites with high local corrosion current densities, while [Y(mbp)₃.H₂O] showing the ability of inhibiting localised corrosion. Such localised corrosion inhibition ability by [Y(mbp)₃.H₂O] was found to be associated with the formation of an inhomogeneous surface film that allows the existence of minor anodes randomly distributing over the surface, leading to low anodic current densities and insignificant general corrosion rather than severe localised corrosion. These results demonstrate a new approach to discovering localised corrosion inhibitors through local electrochemical measurements using electrode arrays.