## 3 Results and Discussion
### Results of Inhibition Efficiency Test of IL1 and IL2 as Corrosion Inhibitor by the EIS Method
IL1 and IL2 have big steric hindrance and high hydrophobicity properties and during the corrosion reaction on carbon steel surfaces, the bulk cations of IL1 and IL2 can easily and directly bind to electrons on the metal surfaces. In addition, the R\({}^{2}\) values of IL1 and IL2 for each curve in Figure 4a showed that the adsorption mechanisms of new ILs follow the Langmuir adsorption isotherm with the R\({}^{2}\) value close to 1 for IL1 and IL2 (i.e., 0.983 and 0.965, respectively) and it is almost linear. The R\({}^{2}\) values of IL1 and IL2 following the Temkin adsorption mechanism were far from linear form as shown in Figure 4b. Table 3 also showed that IL1 and IL2 followed the Langmuir adsorption model with \(\Delta\text{G}_{\text{ads}}\) of \(-35.04\) kJ/mol for IL1 and \(-34.04\) kJ/mol for IL2. In general, these \(\Delta\text{G}_{\text{ads}}\) values show that the adsorption of IL1 and IL2 have occurred on carbon steel surface due to semi-chemical adsorption and or physical adsorption as indicated by their \(\Delta\text{G}_{\text{ads}}\), which is higher than \(-30\) kJ/mol and lower than \(-40\) kJ/mol [40; 41; 42]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**IL** & **Gradient (m)** & **Intercept Value (C)** & \(\mathbf{K_{ads}\) (M\({}^{-1}\))} & \(\mathbf{\Delta G_{ads}\) (k/mol)} \\ \hline
1 & \(2.00\times 10^{-6}\) & \(4.00\times 10^{-5}\) & \(2.50\times 10^{5}\) & \(-35.04\) \\
2 & \(8.83\times 10^{-1}\) & \(6.00\times 10^{-5}\) & \(1.67\times 10^{4}\) & \(-34.04\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the adsorption mechanism determination of IL1 and IL2 following the Langmuir isotherm model. Figure 4: Langmuir adsorption isotherm (**a**) and Temkin adsorption isotherm (**b**) for IL1 and IL2. Kinetics data (activation energy) of IL1 and IL2 were also evaluated by the EIS method following Equation (7) [11; 43]. The activation energy (E\({}_{\text{a}}\)) shows the lowest energy needed to carry out the corrosion reaction [13; 21]. The activation energy (E\({}_{\text{a}}\)) for IL1 and IL2 for the various concentrations at various temperatures is given in Figure 5:  
\[\ln(\text{I}_{\text{corr}})=\ln\text{A}-\frac{\text{E}_{\text{a}}}{\text{RT}} \tag{7}\]  
where A is an empirically Arrhenius constant, I\({}_{\text{corr}}\) is the current density of the corrosion rate of the system, E\({}_{\text{a}}\) is the activation energy of the corrosion process (kJ/mol), R is the ideal gas constant (8.314 J\(\cdot\)mol\({}^{-1}\)K\({}^{-1}\)), and T is the temperature (K). The linear line the equations obtained illustrates the relationship of Y = mX + C which is equivalent to \(\ln\) (I\({}_{\text{corr}}\)) = [\(-\)E\({}_{\text{a}}\)/R] (1/T) + ln A. Based on Equation (7), the graphs were made from the data ln (I\({}_{\text{corr}}\)) versus 1/T (multiplied by 1000) to get a linear relationship as shown in Figure 5. The activation energy data of the corrosion process subsequent to the addition of IL1 and IL2 are summarized in Table 5.  
Table 5 shows that the corrosion rates in the system decreased after the addition of new ILs. The E\({}_{\text{a}}\) values for the control without IL were relatively low, namely 27.5 and 23.9 kJ/mol. These data showed that the corrosion reaction occurred without ILs in the system. After the addition of new ILs, the inhibition of corrosion happened quickly, with E\({}_{\text{a}}\) corrosion reactions increased with the increase in the concentration of ILs. The efficient concentration of IL1 that can inhibit the corrosion rate was 80 ppm with the E\({}_{\text{a}}\) value around 79.7 kJ/mol. While the efficient concentration of IL2 to inhibit the corrosion rate was 100 ppm, the E\({}_{\text{a}}\) value was around 74.4 kJ/mol. The results showed that the optimum concentrations to apply for IL1 and IL2 by using the direct injection method are 80 and 100 ppm, respectively. The direct coating method of IL1 and IL2 achieved corrosion inhibition at a significantly lower concentration of 20 ppm and 18 ppm, respectively.