## 3 Results
### Electrochemical Results  
The polarization studies were carried out on steel samples in 1 M HCl containing different concentrations of essential oil and anethole. The anodic polarization curves at 298 K are shown in Figure 5.  
Figure 4: Change in corrosion rate and inhibition performance of steel plates in 1 M HCl without and with different concentrations of anethole.  
Figure 5: _Cont._  
The electrochemical parameters of the steel plates at different concentrations of the inhibitors are presented in Table 2. The results show that the inhibitory effect of the essential oil reaches a value of up to 81.80% at a concentration of 2.0 mL/L, and that of anethole reaches 84.52% at a concentration of 1.0 mL/L.  
Figures 6 and 7 show the surface condition of steel plates at different concentrations of inhibitors.  
Following the electrochemical testing, varying degrees of pitting and uniform corrosion were visible in the surface morphologies. A reduced number of partially closed corrosion pits was seen with an increase in the content of fennel fruit oil (Figure 6). The reverse tendency of an increase in pit count was observed when the concentration of anethole was elevated (Figure 7). There was an absorbed film on the steel surface (Figures 6a and 7a) that contributed to a decrease in contact between the steel and the aggressive medium. As a result, steel corrosion can be effectively prevented by a reliable layer of absorptive protection.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Medium, L**} & \(\beta_{\text{A}}\)*, & \(\beta_{\text{C}}\) & \(i_{\text{corr}}\), & \(\text{E}_{\text{corr}}\) & \(\text{E}_{\text{corr}}\) & \(\text{E}_{i}\) \\  & **mV/dec** & **mV/dec** & **A/cm2** & **V vs. Ag/AgCl** & **\%** \\ \hline
1 M HCl without inhibitors & 61.2 \(\pm\) 0.6 & 77.2 \(\pm\) 0.7 & 2.28 \(\times\) 10\({}^{-4}\) & \(-\)0.480 & - \\
1 M HCl and & 55.8 \(\pm\) 0.5 & 77.5 \(\pm\) 0.6 & 1.43 \(\times\) 10\({}^{-4}\) & \(-\)0.481 & 37.28 \(\pm\) 0.3 \\
1 M HCl and & 61.7 \(\pm\) 0.6 & 95.2 \(\pm\) 0.69 & 8.22 \(\times\) 10\({}^{-5}\) & \(-\)0.473 & 63.95 \(\pm\) 0.6 \\
1 M HCl and & 71.2 \(\pm\) 0.7 & 98.9 \(\pm\) 0.9 & 4.15 \(\times\) 10\({}^{-5}\) & \(-\)0.471 & 81.80 \(\pm\) 0.8 \\
2.0 mL fennel fruit essential oil & 74.2 \(\pm\) 0.7 & 72.7 \(\pm\) 0.6 & 3.53 \(\times\) 10\({}^{-5}\) & \(-\)0.468 & 84.52 \(\pm\) 0.8 \\
1 M HCl and 1.5 mL anethole & 63.4 \(\pm\) 0.6 & 65.4 \(\pm\) 0.6 & 8.90 \(\times\) 10\({}^{-5}\) & \(-\)0.472 & 60.96 \(\pm\) 0.5 \\
1 M HCl and 2.0 mL anethole & 62.4 \(\pm\) 0.6 & 90.8 \(\pm\) 0.6 & 3.48 \(\times\) 10\({}^{-4}\) & \(-\)0.472 & 52.63 \(\pm\) 0.5 \\ \hline \hline \end{tabular}  
* \(\beta_{\text{A}}\)—anodic Tafel slope; \(i_{\text{corr}}\)—the density of the corrosion current; \(\text{E}_{\text{corr}}\)—corrosion potential; \(\text{E}\)—corrosion inhibition efficiency.  
\end{table}
Table 2: Electrochemical parameters of steel plates at different inhibitor concentrations.  
Figure 5: Representative anodic polarization curves for steel in 1 M HCl without and with different concentrations of fennel fruit essential oil (**a**) and anethole (**b**).  
Figure 6: Representative microstructure images of the plain steel surfaces after the tests in (**a**) 1 M HCl solution; (**b**) 1 M HCl solution with 1.0 mL/L fennel fruit essential oil; (**c**) 1 M HCl solution with 1.5 mL/L fennel fruit essential oil; (**d**) 1 M HCl with 2.0 mL/L fennel fruit essential oil.  
Figure 7: Representative microstructure images of the plain steel surfaces after the tests in (**a**) 1 M HCl solution; (**b**) 1 M HCl solution with 1.0 mL/L anothele; (**c**) 1 M HCl solution with 1.5 mL/L anothele; (**d**) 1 M HCl with 2.0 mL/L anothele.