## 3 Effect of Grain Size and Corrosion Inhibition Mechanism
These coating platforms were created to further enhance the corrosion-resistant effectiveness and to accomplish the hydrophobicity of the formed coated substrates. Only a mild flexion of the Bode graphs at the minimal frequency area and one semicircle in the Nyquist graphs indicated that the integration of distinct loading rates of TiO\({}_{2}\)-NPs within the epoxy polymer metrics had considerably improved the barrier characteristics of the nano-modified coatings. These results may be explained by the significant contribution of the integrated TiO\({}_{2}\)-NPs in varying the framework of the epoxy polymer matrices. The integrated NPs helped to reorganize the polymer metrics through physical interactions caused by Van Der Waal's force, which enables closure of the pore spaces of the epoxy metrics and influences the infiltrated electrolyte to transit a greater length in an attempt to advance the surface layer sorption and result in the effective corrosion inhibition. To create active (inhibitive)/passive (barrier) anti-corrosion coating systems, [PERSON] et al. [62] created a sustainable MOF centered on cerium (Ce-MOF) on GO nanosheets (GO@Ce-MOF) in an aquatic medium. The 1,3,5-benzene tricarboxylic acid used in the fabrication of the  
Figure 19: Illustration displaying the inhibition mechanism of Y\({}_{2}\)O\({}_{3}\)/IMD-modified covering over the surface of the steel. Reprinted with permission from Ref. [35]. MDPI (2021). Ce-MOF NPs produced a dense shape resembling a straw sheaf. The generated NPs were then incorporated into the epoxy matrices using the GO as a host for the Ce-MOF NPs in a nanocontainer. They concentrated on one of the most crucial aspects of employing nano-modified coatings to shield metals from corrosion: their adhesion strength following a mechanical flaw. The formation of OH\({}^{-}\) ions beneath the coating causes coating separation and adhesion reduction. Two events at the metal/coating substrate interface account for this: (1) a deterioration of interfacial adhesive bonds caused by the production of hydroxyl ions, and (2) an increase in pH. In this investigation, a cathodic disbonding analysis was used to explore the coatings' wet adhesion intensity. The Blank/EP specimen was given the largest delamination diameter (11.39 mm), followed by GO/EP (9.69 mm), Ce-MOF/EP (6.6 mm), and GO@Ce-MOF/EP (5.88 mm). The outcomes demonstrate that Ce-MOF NPs considerably increased Ce-MOF/EP's adherence over the metallic surface. The 1,3,5-BTC configuration had a significant number of electron donors, which helps strengthen the bonds between the metal and the coating. The local pH decreased as a result of a reaction between hydroxyl ions and cerium cations that resulted in the formation of insoluble cerium oxides/hydroxides at the cathodic regions. When GO@Ce-MOF/EP was contrasted to the Ce-MOF/EP composite, covering delamination occurred less frequently throughout the experimental period of 24 h due to the regulated discharge of Ce-MOF NPs. Another factor contributing to the GO@Ce-MOF nanoparticles' remarkable barrier characteristics was their active involvement in fixing the micro flaws in the epoxy coating. These NPs might make it easier for corrosive substances to enter the coating/metal interface. Furthermore, in order to generate corrosion inhibitors for the AM60B Mg alloy in a 30% ethylene glycol medium comprising 0.5 M NaCl, [PERSON] et al. [61] created an aluminum terephthalate (AlTp) MOF and its two nanocomposites comprising GO (AlTp/GO) and iron oxide (AlTp/Fe\({}_{2}\)O\({}_{3}\)). For the AlTp, AlTp/GO, and AlTp/Fe\({}_{2}\)O\({}_{3}\), the values of \(\Delta\)Gads\({}^{0}\) were 26.92, 26.85, and 27.83 kJ mol\({}^{-1}\), correspondingly. In this procedure, inhibitory molecules were adsorbed over the metallic substrate by electrostatic interaction. Contrastingly, AGads\({}^{0}\) values found here range within the two magnitudes mentioned, indicating that physisorption and chemisorption were two forms of interaction involved in the adsorption process of the inhibitors upon the AM60B substrate.