# Recent Trends and Progress in Corrosion Inhibitors and Electrochemical Evaluation
## 3 Types of Corrosion Inhibitors
### Composite-Based Corrosion Inhibitors
#### 3.4.3 Silane-Based Composite Coatings  
The technology of organosilane, one of many coating systems, has advanced significantly in recent years. It has attracted the interest of researchers in recent years due to its low volatile organic content, strong anticorrosion, and adhesive qualities on metal substrates. A class of organic-inorganic compounds with silicon as its base called silanes is biocompatible. Silanes easily hydrolyze in aqueous solutions to create silanol groups (SiOH), which allow them to connect to any hydrated metal surface (metal-OH) by creating silicon (Si)-oxygen-metal linkages. Additionally, the silanol groups might engage in siloxane linkages for self-cross-linking (SieOeSi), which would result in the creation of a protective layer chemically attached to metallic substrates [70]. Due to its low density, lightweight nature, good castability, and recyclability, the aerospace, defense, and automobile industries extensively utilize magnesium (Mg) and its alloys. Among the coatings presently available, silane coating has gained extensive use in the anticorrosion sector due to its cost-effectiveness, environmental friendliness, and ease of application. However, the significant utilization of magnesium alloys is hindered by their susceptibility to corrosion. As a result, various surface modifications have been employed to protect magnesium alloys from corrosion. These include polymeric coatings [71], micro  
Figure 6: Schematic representation of anticorrosive coating by encapsulating CIs on a carbon nanosphere. are oxidation (MAO) coatings [72], chemical conversion coatings [73], silane coatings [74], and composite coatings. [PERSON] et al. [75] synthesized silane coating material via the sol-gel method using 3-glycidyloxypropyl trimethoxy silane as the precursor and (3-aminopropyl) trimethoxysilane as the cross-linking agent, and applied it on a mild steel substrate; this resulted in the formation of oxide layer, forming a passivation layer to enhance the corrosion resistance. P-aminothiophenol-doped 3-glycidoxypropyltrimethoxysilane-based sol-gel matrices (PATP-GPTMS) were synthesized by [PERSON] et al. [76] using condensation and hydrolysis processes. The PATP-GPTMS sol-gel produced via a self-assembly process was applied on polished copper (Cu) surface. Furthermore, in a 3.5% sodium chloride (NaCl) media, the ability of PATP-GPTMS/Cu coatings to prevent corrosion has been investigated. All of the findings showed that in an aqueous 3.5% NaCl media, the PATP-GPTMS/Cu coating improved the protection of Cu against corrosion. [PERSON] et al. [77] successfully deposited hybrid films based on polyaniline and polysiloxane moieties on commercial aluminum alloy using N-(3-trimethoxysilpropyl) aniline (AnSi) as a primer for corrosion inhibition. Numerous studies have investigated how a silane layer affects the corrosion resistance of Mg alloys [78]. According to [PERSON] et al. [79] after introducing a three-layer coating, i.e., PEO/silane/epoxy, the impedance data fitting results show that the silane layer has a good impact on enhancing the protective qualities of the epoxy coating. The change diagrams of R\({}_{\text{coat}}\) and R\({}_{\text{ct}}\) values over the duration of immersion in 3.5 wt.% NaCl solution for the coated samples show this. The R\({}_{\text{coat}}\) and R\({}_{\text{ct}}\) values throughout the immersion period were greatly improved by the silane layer. [PERSON] et al. [80] also investigated the surface characteristics of WO\({}_{3}\)-MgO oxide layers formed on AZ31 Mg alloy by micro-arc oxidation. Impedance studies in 0.05 M NaCl corrosive media were carried out to better understand the impacts of WO\({}_{3}\) concentrations on the corrosion behavior of Mg in all samples. The results of the Nyquist plots revealed that samples containing  
Figure 7: SEM images show polished copper (blank), copper submerged in 5 mol HCl, and corrosive media, copper immersed in 5 mol HCl + 5 wt.% GCN, and corrosive media, and copper immersed in 5 mol HCl + 5 wt.% M16 [69] (**a–f**).