# Recent Trends and Progress in Corrosion Inhibitors and Electrochemical Evaluation
## 5 Corrosion Monitoring Techniques
### Scanning Electrochemical Microscopy  
Scanning electrochemical microscopy (SECM) is a technique in which the current that flows through a very small electrode tip (generally an ultramicroelectrode with a tip diameter of 10 pm or less) near a conductive, semiconductive, or insulating substrate immersed in solution is used in the SECM technique to characterize processes and structural features at the substrate as the tip is moved close to the surface. To probe the diffusion layer, the tip can be moved perpendicular to the surface (the z direction), or it can be scanned uniformly across the surface (the x and y direction). In an electrochemical cell, which often also includes other electrodes (such as auxiliary and reference) the tip and substrate form a component [154]. Collection modes, where products electrogenerated at the substrate are detected at the tip (kept at constant potential or operated in the cyclic voltammetry mode), and feedback modes, where the impact of the substrate on the tip current is monitored, are among the modes of operation that have been taken into consideration. For the study of structures and operations in micrometer- and sub-micrometer-sized systems, SECM is a useful instrument. It can examine chemical processes at liquid-liquid, liquid-air, and  
Figure 18: Ti–13 Zr–13 Nb LEIS maps recorded at EOC in saline solution at 37 °C: the non-nodized alloy (**a**), the anodized alloy (**b**), the non-nodized alloy (**c**), and the anodized alloy (**d**) [152]. solid-liquid interfaces as well as electron, ion, and molecule transfers. Research into a wide range of phenomena, from metal corrosion to adsorption to metabolism in single living cells, is made possible by this adaptability [155]. SECM is an electrochemically based scanning probe microscope (SPM) method. Figure 19 illustrates how the movement of a microelectrode (ME) in close proximity to the interface being studied enables the application of a variety of experimental techniques that can be divided into amperometric and potentiometric operations depending on either sensing faradaic currents or probing potential values due to concentration distributions caused by the corrosion process [156]. SECM is used to characterize the topography and redox activities of the metal/electrolyte solution interface because to its high spatial resolution and electrochemical sensitivity in comparison to other local probe techniques that only characterize morphologically. Due to its direct detection of chemical species in localized corrosion processes with high spatial resolution, it would be more beneficial [157]. The ASTM standard D1141-98 (2013) was examined by [PERSON] et al. to see whether guar gum-grafted 2-Acrylamido-2-Methylpropanesulfonic acid (GG-AMPS) might reduce the corrosion of carbon steel. The localized corrosion activity was identified by SECM. According to the technique, the produced current increased as the probe was lowered towards the surface of the carbon steel. This might be because the probe made direct contact with the conductor-acting metal surface shown in Figure 20a. When the identical probe was brought closer to the steel surface with GG-AMPS coating, a lower current was seen as a result of the insulating qualities of the steel surface's (Figure 20b). In conclusion, the steel acts as a conductor without the GG-AMPS coating layer and the probe only detects a lower current. On the contrary, the steel acts as a strong insulator with the coating layer present, and the probe records a higher current. Compared to synthetic seawater, the Ecorr values for the GG-AMPS coating also exhibit variances. At 600 mg/L, the GG-AMPS coating has the highest inhibitory efficacy of 92.5% in aggressive media [158; 159]. With the use of the SECM, [PERSON] et al. discovered a new technique for measuring pH during the corrosion process; they used antimony tips because their dual-function characteristics of this material allow the combined amperometric/potentiometric operation of the SECM.