# Recent Trends and Progress in Corrosion Inhibitors and Electrochemical Evaluation
## 3 Types of Corrosion Inhibitors
### Organic Corrosion Inhibitors
According to this observation, Ph-CN and Ph-NO\({}_{2}\) should have better anticorrosion properties than pure benzene, in which only the aromatic ring participates in charge sharing. In this case, the increase in inhibition and efficiency can be attributed to an increase in the molecular size and electron donating ability of the -CN and -NO\({}_{2}\) heteroatoms [46]. [PERSON] et al. [47] designed a CI with different methods with the CI carrying more polar heads and alkylene linkers. As such, the adsorption of the CI on copper surfaces could increase by two or more polar groups. The chelating action of heterocyclic molecules as corrosion inhibitors is based on the formation of an insoluble physical diffusion barrier on the electrode surface, which could prevent metal reaction as well as dissolution. With this, they employed a benzothiazazole heterocyclic ring as a polar head to design a new CI. Schiff bases (CSBs) made of chitosan were examined as CIs by [PERSON] et al. [48]. According to this study, CSBs are stable and do not hydrolyze in the majority of experimental conditions. Three primary reactive functional groups are present in chitosan (CH), including amino (-NH\({}_{2}\)), 1-hydroxyl (-CH\({}_{2}\)OH), and 2-hydroxyl (>CH-CH\({}_{2}\)OH) substituents at C-2, C-3,  
Figure 4: Annual corrosion rate with organic inhibitors in relation to time and for various acid molarities [41]. and C-6, respectively. CH and CSBs are effective for covering and safeguarding metal surfaces, such as steel and mild steel (MS) due to their polymeric composition. [PERSON] et al. [49] used Ch-Cr-SB as a corrosion-resistant coating for AZ91E alloy in a 3% NaCl solution in their study. The anticorrosive potential of Ch-Cr-SB was investigated at various concentrations. The results show that increasing Ch-Cr-SB concentration increases the effectiveness of its corrosion protection or decreases the rate of corrosion, while increasing temperature has the reverse effect. [PERSON] et al. [50] developed triethanolamine (TEA), an organic corrosion inhibitor covered with an epoxy finish and encapsulated. The sustained anticorrosion ability, made possible by its self-healing capability, was examined to enhance the alloy's ability to resist corrosion. According to EIS studies, the inhibition efficiency (IE) was 85% when metal experienced mild corrosion. When the local pH level starts to change, the inhibitor layer starts to form, which triggers the release of TEA. Moreover, it also shows self-healing properties. In the next section we discussed more about self-healing techniques. Samples embedded in nanocapsules show suppression of corrosion activity and provide long-term anticorrosion performance, especially in chloride-rich environments [51]. [PERSON] et al. [52]. gave a comprehensive review on isatin and its derivatives as a new, efficient, and green N-heterocyclic class of organic corrosion inhibitors. The intolerable toxicity of current, albeit very successful, corrosion control techniques has increased the demand for novel, safe, and environmentally friendly corrosion inhibitors. The substantial expansion in technological skills related to the development of new organic corrosion inhibitors coincides fortunately with this demand. Although they have advantages in preventing corrosion, they also have some drawbacks that must be taken into account. Because of factors, like temperature changes, contact with corrosive substances, or extended exposure to the environment, organic corrosion inhibitors frequently offer only short-term protection that may deteriorate over time. It could be necessary to periodically reapply and monitor these inhibitors [53].