## 3 Results and Discussions
### Electrochemical Analysis
Therefore, through the adsorption of corrosion inhibitors on the metal surface, an organic inhibitor layer gradually forms and is capable of replacing the water molecules present at the surface electrode. As the concentration of inhibitors increases, the protective layer becomes denser and, consequently, becomes an effective barrier for the metal surface against the aggressive attack of corrosive species. The inhibitor efficiency (IE) was calculated from EIS data using Equation (1) and is listed in Table 1[1; 20]:  
\[\text{IE}\left(\%\right)=\left(1-C_{\text{eff}}/C_{\text{eff}0}\right)\times 100 \tag{1}\]  
where \(C_{\text{eff}}\) and \(C_{\text{eff}0}\) represent the double layer capacitance (from EIS) in the presence and absence of the inhibitor, respectively, or alternatively, the corrosion current density (from polarization curves) in the presence and absence of the inhibitor, respectively. The IE values exceed 86% in the presence of EEA4 NB and increase with the inhibitor concentration. The highest value is obtained in a 3% NaCl solution with 5 mM EEA4 NB, indicating the formation of a protective layer on the metal surface. A concentration of 5 mM is sufficient to form a protective inhibitor layer that can block the penetration of aggressive Cl ions. This concentration ensures the formation of a compact and less porous protective layer. For EEA4 NB concentrations lower than 4 mM, the coverage of the metallic surface is incomplete and may not fully protect the steel surface. In such cases, Cl ions can reach the carbon steel surface and promote corrosion. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{C_{inh}}\)**, mM/SD \({}^{*}\)** & \(R_{\text{s}}\)**, \(\mathbf{\Omega}\cdot\mathbf{cm^{2}}\)** & \(R_{\text{ct}}\)**, \(\mathbf{\Omega}\cdot\mathbf{cm^{2}}\)** & \(C_{\text{eff}}\)**-\(T\), \(\mathbf{F}\cdot\mathbf{cm^{-2}/s\varphi^{-1}}\)** & \(CPE_{\text{eff}}\)**-\(P\), (\varphi)** & **IE, \%** \\ \hline
0 & 11.92 \(\pm\) 0.21 & 36 \(\pm\) 12 & 7.93 \(\times\) 10\({}^{-3}\)\(\pm\) 0.19 \(\times\) 10\({}^{-4}\) & 0.80 \(\pm\) 0.03 & \\ \hline
0.5 & 12.3 \(\pm\) 0.82 & 430 \(\pm\) 9 & 1.05 \(\times\) 10\({}^{-4}\)\(\pm\) 1.03 \(\times\) 10\({}^{-4}\) & 0.76 \(\pm\) 0.11 & 86.73 \(\pm\) 2.01 \\ \hline
1 & 12.3 \(\pm\) 0.11 & 440 \(\pm\) 9 & 9.05 \(\times\) 10\({}^{-4}\)\(\pm\) 8.01 \(\times\) 10\({}^{-6}\) & 0.81 \(\pm\) 0.07 & 88.60 \(\pm\) 0.24 \\ \hline
2 & 11.69 \(\pm\) 0.41 & 872 \(\pm\) 6 & 5.80 \(\times\) 10\({}^{-4}\)\(\pm\) 0.39 \(\times\) 10\({}^{-5}\) & 0.82 \(\pm\) 0.05 & 92.70 \(\pm\) 1.27 \\ \hline
3 & 11.62 \(\pm\) 1.12 & 967 \(\pm\) 11 & 3.80 \(\times\) 10\({}^{-4}\)\(\pm\) 0.72 \(\times\) 10\({}^{-5}\) & 0.85 \(\pm\) 0.04 & 95.22 \(\pm\) 1.56 \\ \hline
4 & 11.6 \(\pm\) 0.98 & 993 \(\pm\) 12 & 2.80 \(\times\) 10\({}^{-4}\)\(\pm\) 0.03 \(\times\) 10\({}^{-4}\) & 0.87 \(\pm\) 0.05 & 96.48 \(\pm\) 2.11 \\ \hline
5 & 11.53 \(\pm\) 0.91 & 1130 \(\pm\) 26 & 2.70 \(\times\) 10\({}^{-4}\)\(\pm\) 0.08 \(\times\) 10\({}^{-4}\) & 0.88 \(\pm\) 0.05 & 96.60 \(\pm\) 5.03 \\ \hline \end{tabular} \({}^{*}\): Standard deviation.  
\end{table} 
Table 1: Corrosion parameters obtained from EIS measurements for carbon steel in 3% NaCl without and with the inhibitor EEA4 NB. The number of binding sites on the metal surface/degree of surface coverage affect \(C_{dl}\). \(C_{dl}\) decreases when the ion species present in the solution are adsorbed on the metal surface, and the available number of binding sites decreases with an increase in immersion time. Consequently, the rate of adsorption decreases over time. In Figure 2a, the presence of two regions in the decay of \(C_{dl}\) with immersion time was observed. The first stage of adsorption reveals the presence of numerous available binding sites for ionic species, while the second stage exposes the presence of an irreversible organic layer on the metal surface.