## 3 Results and Discussion
### Results of Inhibition Efficiency Test of IL1 and IL2 as Corrosion Inhibitor by the EIS Method
Thus, the carbon steel surface was protected from polar and corrosive environments like water and 1% NaCl, which can increase the corrosion rate. In this study, the adsorption mechanisms of a new IL-based corrosion inhibitor on carbon steel surfaces were also determined. The adsorption mechanisms on carbon steel surfaces follow the Langmuir isotherm model and the Temkin isotherm model due to the ILs interaction with carbon steel surfaces assume the gas phase. Initially corrosion inhibitors were made in the gas phase in order to form a thin layer on the surface of carbon steel [37]. The Langmuir isotherm model was developed for observing the mechanism of the absorption and desorption of the molecules on the surface of the adsorbate with zero accumulation rate, which can be used to quantify the capacity of various concentrations of adsorbents. Meanwhile, the Temkin isotherm model was developed to observe the interaction between adsorbents and adsorbates at extremely large and low concentration values, and this model assumes that adsorption heat as a function of temperature. Resistance values of each IL were measured by the EIS method at the best condition (temperature 25 \({}^{\circ}\)C). The resistance on the carbon steel surface increased after the addition of ILs indicates that the corrosion reaction was not occurring, whereas, in the control, corrosion reaction took place quickly and spontaneously. The spontaneity or non-spontaneity of corrosion reaction on the carbon steel surface was determined by the corrosion inhibition performance test. The determination of Langmuir adsorption mechanism of IL1 and IL2 were calculated by using Equations (2) and (3) and generated the data of \(\theta\), C/\(\theta\), and In C. Below is Equation (2) for the Langmuir adsorption isotherm [38]:  
\[\theta=\frac{\text{bC}_{\text{inh}}}{1+\text{bC}_{\text{inh}}} \tag{2}\]  
\(\theta=\) degree of surface cover;  
\(\text{b}=\) adsorption coefficient;  
\(\text{C}_{\text{inh}}=\) inhibitor concentration. The other form of the equation above is:  
\[\frac{\text{C}}{\theta}=\text{C}+\frac{1}{\text{b}} \tag{3}\]  
The intercept section (b) equal to the Kads value (the adsorption process constant) procured by using the relationship Y= mX + C, according to the following equations:  
\[\text{b}\ =\ \text{K}_{\text{ads}}=\frac{\theta}{C(1-\theta)} \tag{4}\]  
\[\Delta\text{G}_{\text{ads}}=-\text{RT}\ln(55,55\text{K}_{\text{ads}}) \tag{5}\]  
Based on the two equations above (Equations (4) and (5)), the values of the free energy adsorption (\(\Delta\text{G}_{\text{ads}}\), kJ/mol) of IL1 and IL2 can be determined. The \(\Delta\text{G}_{\text{ads}}\) of each IL is shown in Table 3. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Temperature** & \multicolumn{2}{c}{**IE\%**} \\ \cline{2-3}
**(\({}^{\circ}\)C)** & **20 ppm of IL1** & **18 ppm of IL2** \\ \hline
25 & 99.3 \(\pm\) 0.5 & 99.3 \(\pm\) 1.0 \\
35 & 32.5 \(\pm\) 0.4 & 61.9 \(\pm\) 0.6 \\
45 & 24.0 \(\pm\) 0.3 & 50.6 \(\pm\) 1.0 \\
55 & 12.5 \(\pm\) 0.5 & 33.6 \(\pm\) 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Percent inhibition efficiency (IE%) of the carbon steels directly coated with IL1 and IL2. In addition, the determination of the adsorption mechanism of IL1 and IL2 was also carried out by the Temkin adsorption isotherm. The calculation of the Temkin isotherm adsorption mechanism was carried out using Equation (6) [39]. The calculated results of the ILs are described in the linear graph as shown in Figure 4:  
\[\theta=\frac{\text{RT}}{\text{b}}\ln(\text{C}_{\text{inh}}) \tag{6}\]  
At the same step, the free energy of the adsorption values (\(\Delta\text{G}_{\text{ads}}\), kJ/mol) of IL1 and IL2 were also determined by using the Temkin isotherm model as shown in Table 4. Figure 4 shows the results of the data described in the linear graph of Langmuir and Temkin adsorption isotherms. Figure 4 shows that IL1 and IL2 showed a better fit in the Langmuir adsorption model than the Temkin adsorption model.