## 3 Effect of Grain Size and Corrosion Inhibition Mechanism
Considering a multilayer adsorbate over an adsorbent, physical adsorption has been shown to possess a minimal enthalpy of adsorption (\(<\)\(-\)40 kJ/mol), whereas chemical adsorption (chemisorption) entails a chemical reaction involving the adsorbate and adsorbent and typically results in the emergence of chemical bonds. It also has a greater enthalpy of adsorption, ranging from 80 to 240 kJ/mol [98; 99]. To further explain the inhibition process of the nano-modified coatings, some researchers have documented the adsorption behavior of NP-based corrosion inhibitors or coatings. For instance, in an experiment to increase the effectiveness of inhibition for an St37 steel substrate, a proposed nano-modified coating created by inserting silver nanoparticles (AgNPs) formed in situ through reduction of AgNO\({}_{3}\) utilizing organic honey in carboxymethyl cellulose (CMC) matrices was used by [PERSON] et al. [100]. When the system temperature was raised to 40, 50, and 60 \({}^{\circ}\)C, correspondingly, the IE% declined to 61.0%, 60.9%, and 60.8%. CMC molecules were physically adsorbed over the metallic substrate in the acid medium, according to the fluctuation of \(\eta\) with \(\Delta\)Gads\({}^{0}\) value and temperature. Similarly, in order to explain the corrosion-inhibition mechanism of nanocoating, [PERSON] et al. [35] created polymeric nanocomposite coatings that were altered to incorporate CIs. The CIs (imidazole)-loaded yttrium oxide NPs employed in this study were added to the epoxy composition before being deposited on the substrate material. According to EIS, the infused material (Y\({}_{2}\)O\({}_{3}\)/IMD) appeared to be pH-responsive, a characteristic that aids in the liberation of the inhibitor from the particulates and enhances corrosion mitigation. After the electrolyte first contacts metal, corrosion action caused a localized pH variation. Because the hydrolysis of Fe ions facilitated the CIs' escape, it was anticipated that the pH at the damaged region would approach acidic levels in the anodic zones. As per the conceptual layout shown in Figure 19, the inhibitory impact reported for the Y\({}_{2}\)O\({}_{3}\)/IMD-modified covering was caused by the adsorption capability of imidazole over the surface of the steel. For the generation of a preventative coating featuring enhanced corrosion protection and self-healing capabilities, [PERSON] et al. [101] studied conducting polyaniline (PANI)-based paint formulations. The regulated inhibitor discharge process suggested that corrosion-inhibitory dopant ions were discharged via the breakdown of PANI as a result of metal electrolysis at tiny holes or an ion-exchange mechanism. The dopant anions that were discharged created a second physical shield that prevented oxygen reduction or the transit of aggressive anions. These PANI-based coatings are often known as \"smart coatings\" because the dopant anion is discharged when needed, or more specifically when the coating is degraded and results in metallic corrosion and, therefore, a reduction in PANI. Along with the production of oxide, complexes comprising the metallic ions were generated on the metallic substrate, forming extensive anodic shielding. Furthermore, in these circumstances, PANI discharged the dopant anion (DBSA), which developed complexes with Fe and resulted in the passivation of steel. The lowering of PANI, which indicated its physical absorption over the metallic substrate, caused the discharge of inhibitory dopants and superior corrosion mitigation. Moreover, the effects of incorporating various loading proportions of TiO\({}_{2}\)-NPs within pristine epoxy resin were examined as an aspect of preparation of epoxy-TiO\({}_{2}\) nanocomposite coatings using the solvent intercalation technique with the use of sonication [102]. In this experiment, the epoxy polymeric resin was altered with polydimethylsiloxane (PDMS), and distinct stacking ratios of TiO\({}_{2}\)-NPs were presented to the altered polymer matrices to generate PDMS-reconfigured epoxy nanocomposite coating structures.