## 3 Results and Discussion
### Potentialorization Curves  
Figure 4 represents the potentiodynamic polarization curves of the carbon steel electrode immersed in 1 M HCl solutions with different contents of TSCA at 298 K. It can be observed that the polarization curves move in the direction of decreasing current density in the presence of TSCA. This result demonstrates that the anode and cathode reaction of the carbon steel electrode were inhibited by TSCA in the corrosion solution.  
The polarization parameters, including corrosion potential (\(E_{\text{corr}}\)), corrosion current density (\(i_{\text{corr}}\)), and cathodic and anodic Tafel slopes (\(\beta_{\text{c}}\) and \(\beta_{\text{a}}\)) are derived from the Tafel polarization region as the steel was not corroded via localized corrosion with the formation of pits [44; 45; 46]. The results are listed in Table 3. The shift in \(E_{\text{corr}}\) is less than 10 mV, indicating that TSCA works as a mixed-type inhibitor inhibiting both the anode and cathode electrochemical reactions. In addition, slight shifts in \(\beta_{\text{c}}\) and \(\beta_{\text{a}}\) can also be observed in the table. This result demonstrates that the electrochemical reaction of carbon steel remains unchanged, which is in line with the EIS results. The decrease in corrosion current density of carbon steel with TSCA concentration increase reveals the inhibition effect of TSCA on carbon steel. The corresponding inhibition efficiencies (\(\eta_{\text{E}}\)) at different concentrations of TSCA can be calculated by the following equation:  
\[\eta_{\text{T}}=\frac{i^{0}_{\text{corr}}-i^{1}_{\text{corr}}}{i^{0}_{\text{ corr}}}\times 100\% \tag{5}\]  
where \(i^{0}_{corr}\) and \(i^{1}_{corr}\) are the fitted corrosion current densities of carbon steel in the absence and presence of TSCA inhibitor, respectively. The calculated inhibition efficiencies at different concentrations of TSCA are also listed in Table 3. They are in good accordance with the calculated inhibition efficiencies in weight loss and electrochemical impedance spectroscopy measurements. The highest inhibition efficiency of 97.3% can be obtained at 40 mg/L, demonstrating that TSCA is an effective inhibitor for carbon steel. The increase in inhibition efficiency with increasing TSCA concentration is related to the adsorption  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \(C_{\text{TSCA}}\) (mg:L\({}^{-1}\)) & \(R_{\text{S}}\) (\(\Omega\cdot\)cm\({}^{2}\)) & \(C_{\text{dl}}\) (10\%/s\({}^{-1}\cdot\Omega^{-1}\cdot\)cm\({}^{-2}\)) & \(n\) & \(L\) (H-cm\({}^{2}\)) & \(R_{\text{L}}\) (\(\Omega\cdot\)cm\({}^{2}\)) & \(R_{\text{ct}}\) (\(\Omega\cdot\)cm\({}^{2}\)) & \(\eta_{\text{E}}\) (\%) \\ \hline
0 & 0.79 & 208.52 & 0.80 & 35.17 & 3.46 & 18.67 & - \\
1 & 0.79 & 134.26 & 0.93 & 113.57 & 53.22 & 52.05 & 64.1 \\
10 & 0.84 & 86.88 & 0.92 & 302.42 & 187.53 & 113.61 & 83.6 \\
20 & 0.94 & 68.23 & 0.91 & 756.41 & 528.90 & 247.73 & 92.5 \\
40 & 0.77 & 49.83 & 0.91 & 1183.72 & 734.68 & 504.43 & 96.3 \\ \hline \end{tabular}
\end{table}
Table 2: Impedance parameters and corresponding inhibition efficiency for carbon steel immersed in 1 M HCl solutions with different contents of TSCA.  
Figure 4: Potentiodynamic polarization curves of the carbon steel electrode immersed in 1 M HCl solutions with different contents of TSCA at 298 K.  
amount of TSCA on the carbon steel surface. A higher adsorption amount of TSCA increases the steric hindrance and thereby insulates the ions from the carbon steel surface [47].