(Invited) Combined Electrochemical and Surface Analytical Techniques for Probing Complex Multi-Scale Localised Corrosion of Metals and Alloys: An Overview

Localized corrosion processes are dynamic, initiating from micro-sized event and propagating into macro-sized corrosion problems. This attribute suggests that in order to fully understand localized corrosion, there is a need of characterization techniques that have appropriate temporal and spatial resolutions for probing and visualizing pre-existing electrode inhomogeneity and the propagating electrochemical heterogeneity at various length and time scales [1]. Over the past decades various electrochemical and analytical techniques have been developed and utilized to understand the influence of complex hetero-structures on corrosion initiation and propagation of metals and alloys. For instance, scanning probe techniques such as scanning Kelvin probe force microscopy (SKPFM) [2], confocal scanning laser microscope [3], nanotomography [4], atom probe tomography (APT) [5], capillary-based micro-electrochemical test [6] have been used to achieve the high temporal and spatial resolution required for probing localized corrosion initiation. However, it should be noted that these techniques and methods often have limitations in terms of either relating the metastable events to complex micro or even nano structures of alloys or correctly assigning the current transients to localized events in longer exposure times due to poor spatial resolutions because the results are generally averaged over the whole electrode surface. A method that was developed to address this issue is an electrochemically integrated multi-electrode array, often referred to as the wire beam electrode (WBE) [1], that has been described as a rapid, quantitative method to measure localized corrosion of metals and especially steels with a capability to monitor quasi in-situ localized corrosion processes on material surfaces [1, 7-9], often used in combination with complementary techniques such as scanning vibrating electrode [7] and galvanic noise technique and optical profilometry (Figure 1)[9].