## 3 Results and Discussion
### EIS Measurements  
The EIS measurement results of CS immersed in corrosive media by PCA-GLU are plotted in the Nyquist plot, as shown in Figure 4. In the Nyquist diagram, the diameter of the semicircular impedance curves increases, which means that the corrosion efficiency decreases [27]. It was found that after adding PCA-GLU, the impedance diameter increases \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Black** & \begin{tabular}{c} **100** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **200** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **300** \\ **(mg/L)** \\ \end{tabular} & \
\begin{tabular}{c} **400** \\ **(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **500** \\ **(mg/L)** \\ \end{tabular} \\ \hline \(-\)E\({}_{\text{corr}}\) (mV) & 575 & 533 & 534 & 579 & 828 & 899 \\ I\({}_{\text{corr}}\) (A) & 3.872 \(\times 10^{-5}\) & 1.793 \(\times 10^{-5}\) & 1.171 \(\times 10^{-5}\) & 1.643 \(\times 10^{-6}\) & 1.413 \(\times 10^{-6}\) & 2.848 \(\times 10^{-6}\) \\ H (\%) & - & 55.09 & 69.76 & 95.76 & 96.35 & 92.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Corrosion current density and corresponding inhibition efficiencies for Q235 in 3.5 wt% NaCl solution of PCA-GLU. Figure 3: Polarization curve of Q235 in a 3.5 wt% NaCl solution containing PCA-GLU. significantly, showing that the polymer has a good corrosion inhibitory effect on carbon steel. The best-fitting equivalent circuit model analyzes the EIS spectrum of the PCA-GLU in the image to simulate the electrolytic process of the electrode surface. The circuit shown in Figure 5 is composed of charge transfer resistance (Rct), film resistance and capacitance (Rf and Qf), solution resistance (Rs), and a constant phase element (CPE). These impedance parameters are listed in Table 2. Based on the value of the corrosion charge transfer resistance in the table, the corrosion efficiency can be calculated using the following formula:  
\[\eta=\frac{Rct-Rct^{0}}{Rct}\times 100\% \tag{2}\]  
where \(Rct^{0}\) and \(Rct\) represent the total charge transfer resistance of the blank solution and the PCA-GLU solution. The electrochemical impedance curve is divided into two parts: one is the charge transfer process in the high-frequency region, and the other is the diffusion process in the low-frequency region. As the concentration of PCA-GLU increases (except 500 mg/L), the diameter of the impedance spectrum increases, indicating a higher Rct and a gradual decrease in the corrosion rate. From the fitting parameters of the EIS in Table 2, as the concentration rises, the Rct on the surface of carbon steel decreases, and the corrosion inhibition rate rises. When the concentration of the corrosion inhibitory dose is 400 mg/L, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **R\({}_{\text{s}}\)** & **CPE\({}_{\text{dl}}\)** & **R\({}_{\text{f}}\)** & **R\({}_{\text{ct}}\)** & **\(\eta\)** \\  & **(\(\Omega\cdot\text{cm}^{2}\))** & **(S\(\cdot\text{sec}^{\text{n}}\)/cm\({}^{2}\))** & **(\(\Omega\cdot\text{cm}^{2}\))** & **(\(\Omega\cdot\text{cm}^{2}\))** & **(\%)** \\ \hline blank & 6.659 & \(21.5\times 10^{-4}\) & 37.55 & 198 & - \\
100 mg/L & 6.492 & \(16.3\times 10^{-4}\) & 22.64 & 353 & 51.00 \\
200 mg/L & 6.791 & \(8.75\times 10^{-4}\) & 28.52 & 405 & 65.84 \\
300 mg/L & 17.51 & \(2.47\times 10^{-4}\) & 38.88 & 1408 & 92.31 \\
400 mg/L & 16.1 & \(2.51\times 10^{-4}\) & 147.1 & 2161 & 96.73 \\
500 mg/L & 64.92 & \(9.34\times 10^{-5}\) & 61.19 & 1913 & 90.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The inhibition efficiency and EIS parameters of Q235 in 3.5 wt% NaCl solution containing different concentrations of PCA-GLU. Figure 4: [PERSON] plots for Q235 in 3.5 wt% NaCl solution with different concentrations of PCA-GLU. the corrosion rate reaches its peak value, and after this concentration, a threshold phenomenon occurs. According to the data in Table 2, the change in charge transfer resistance (\(Rct\)) is much larger than the change in metal surface film resistance (\(Rf\)).