## 3 Results and Discussion
### Results of Inhibition Efficiency Test of IL1 and IL2 as Corrosion Inhibitor by the EIS Method
IL2 has better corrosion inhibition performance than IL1 due to higher hydrophobicity. The effect of free electrons from the oxygen  
Figure 5: Graphs of the activation energy (E\({}_{\text{a}}\)) determination (Ln(I\({}_{\text{corr}}\)) towards the 1000/T) subsequent to the addition of IL1 (**a**) and IL2 (**b**) in various concentrations. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & & & & & \\ \cline{2-7} II & \multirow{2}{*}{**Control**} & \multicolumn{6}{c}{**Concentration of IL (ppm)**} \\ \cline{3-7}  & & **20** & **40** & **60** & **80** & **100** & **120** \\ \hline \(1\) & 27.5 & 39.3 & 60.2 & 64.5 & 79.7 & 76.7 & 77.0 \\ \(2\) & 23.9 & 37.2 & 52.0 & 67.1 & 71.0 & 74.4 & 72.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: E\({}_{\text{a}}\) corrosion reaction subsequent to the addition of IL1 and IL2 to 1% NaCl. atom of the hydroxyl group helped to inhibit the oxidation process on carbon steel surfaces [40; 41]. Three butyl chains of IL2 increased corrosion inhibition performance. The thermodynamic parameters of the corrosion inhibition process were also investigated. The thermodynamic parameters were very important to show whether the corrosion inhibition reaction in the system was occurring. Thermodynamic parameters can be obtained from Equation (8) below [42]. \[\ln\frac{\mathrm{I_{corr}}}{\mathrm{T}}=\ln\frac{\mathrm{R}}{\mathrm{Nh}}+ \frac{\Delta\mathrm{S^{*}}}{\mathrm{R}}-\frac{\Delta\mathrm{H^{*}}}{\mathrm{ RT}} \tag{8}\]  
where R is the constant of ideal gas (J-mol-1K-1), N is the Avogadro number (mol-1), h is the Plank constant (\(6.63\times 10^{-34}\) J-s-1), \(\Delta\mathrm{S^{*}}\) is the change of entropy of corrosion inhibition process (J-mol-1), \(\Delta\mathrm{H^{*}}\) is the change of enthalpy of corrosion inhibition process (J-mol-1), T is the temperature operation (K), and \(\mathrm{I_{corr}}\) is the current of corrosion (Ampere) which can be obtained from Equation (9):  
\[\mathrm{I_{corr}}=\frac{\mathrm{K}}{\mathrm{R_{P}L}} \tag{9}\]  
where K is an empirical constant which has a value of 0.02 V, \(\mathrm{R_{P}}\) is the value of resistance in the system (ohm-cm2), and L is the diameter of the metal used during measurement (mm). The analysis of ln(I_{corr}/T) to 1/T was carried out by the following linear equation Y = mX + C corresponding to ln(I_{corr}/T) = [-\(\Delta\)H^*/R] (1/T) + [ln(R/nh) + \(\Delta\)S^*/R]. The interpretation and analysis of ln(I_{corr}/T) to 1/T graphs of IL1 and IL2 as shown in Figure 5(a,b) were based on the calculated data using Equation (8). The free energy values of IL1 and IL2 calculated by Equation (10) are presented in Figure 5(c,d). The thermodynamic parameters of IL1 and IL2 as corrosion inhibitors on carbon steel surface in 1% NaCl are summarized in Table 6.  
\[\Delta\mathrm{G^{*}}=\Delta\mathrm{H^{*}}-\mathrm{T}\Delta\mathrm{S^{*}} \tag{10}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Concentration of IL (ppm)**} & \multicolumn{2}{c}{**IL1**} & \multicolumn{2}{c}{**IL2**} \\ \cline{2-5}  & \(\Delta\)H* (kJ/mol) & \(\Delta\)S* (J/mol) & \(\Delta\)H* (kJ/mol) & \(\Delta\)S* (J/mol) \\ \hline
0 & 27.5 & –248.0 & 23.9 & –258.8 \\
20 & 39.3 & –212.1 & 37.2 & –218.9 \\
40 & 60.2 & –147.6 & 52.0 & –172.9 \\
60 & 64.5 & –134.5 & 57.1 & –125.9 \\
80 & 79.7 & –87.0 & 71.0 & –114.4 \\
100 & 76.7 & –95.9 & 74.4 & –103.8 \\
120 & 77.0 & –95.0 & 72.2 & –110.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Thermodynamic parameters of IL1 and IL2 as corrosion inhibitors on carbon steel surface in 1% NaCl. Figure 6: \(Cont.\)  
The results in Table 6 show that IL1 and IL2 thermodynamically inhibit the corrosion rate in the brackish water system, which was indicated by the increase in the \(\Delta\)H* and \(\Delta\)S* values. In the blank the required energy for the corrosion reaction (\(\Delta\)H*) was very low, such as the 27.5 kJ/mol and \(\Delta\)S* value was \(-\)248.0 J/mol.