## 3 Results and Discussion
### The Results of EIS Tests
As can be seen in this figure, the largest diameter of the semicircles is in the presence of the mixture. Thus, the mixture of BPE and RSE has a higher inhibition efficiency for corrosion control than only BPE or RSE in HCl solution. Therefore, the EIS results also confirm the occurrence of synergistic inhibition between BPE and RSE and the enhancement of inhibition efficiency. The Bode plot of the EIS tests is shown in Figure 7. As depicted in this figure, the loop size in the presence of green corrosion inhibitors was larger than in their absence in the acidic environment. This indicates corrosion protection in the presence of the inhibitors used. This effect was enhanced by increasing the inhibitor concentration. These figures show that 750 ppm is the optimal value for banana peel and rice straw extracts. In addition, the best mixing ratio is 40:60 banana peel and rice straw. These results are completely consistent with the weight loss results. The phase angle graphs of the EIS tests are shown in Figure 8. As can be seen, the phase angle was increased by adding green corrosion inhibitor to the solution. In this case, the phase angle was increased by increasing the concentration of the extract. The figure shows that the optimum concentration is 750 ppm. Moreover, the banana peel and rice straw mixture showed the best performance at a mixing ratio of 60:40 BPE:RSE. The electrochemical equivalent circuit was also used to analyze the impedance characteristics, as shown in Figure 9. The system used consists of \(R_{s}\) (HCl solution resistance), \(R_{CT}\) (charge transfer resistance), and CPE (constant phase element). This test was carried out in the absence (blank case) and in the presence of green corrosion inhibitors under static conditions. The results obtained from this analysis are presented in Table 1. It should be noted that the inhibition efficiency was determined using the following formula:  
\[Inhibition\ efficiency\ (IE)=\frac{R_{CT1}-R_{CT0}}{R_{CT1}}\times 100 \tag{6}\]where \(R_{CTI}\) and \(R_{CT0}\) are related to the blank case (0 ppm) and the solution with the inhibitor (ohm\(\cdot\)cm\({}^{2}\)). As shown in Table 1, the \(R_{CT}\) values increased with the increase of inhibitor concentration, and as a result, the inhibition efficiency increased. For the extracts, the optimum concentration of steel corrosion protection was 750 ppm. In addition, rice straw extract showed better results than banana peel extract. These results are consistent with those obtained in the weight loss tests. In addition, the best inhibition performance was obtained by mixing banana peel and rice straw in a ratio of 40:60. The inhibition efficiencies of banana peel, rice straw, and their mixture (40:60) were 78.18, 95.19, and 96.34% at 750 ppm, respectively. Potentiodynamic polarization tests were completed by determining the corrosion current density for the extracts at different concentrations and for the mixture at different mixing ratios. In addition, a blank test (without inhibitor addition) was completed. The experiments were carried out at 35 \({}^{\circ}\)C. In order to verify the accuracy of used data, a comparison of experimental and theoretical values was performed by electrochemical frequency modulation technique using a capacity of 10 mV by defining two causal factors. These factors corresponded to the standard values 2 and 3. The obtained results are  
Figure 7: Bode plots of EIS tests for steel specimens in HCl solution in the absence and presence of green corrosion inhibitors: banana peel extract (**a**), rice straw extract (**b**), mixture of extracts at different mixing ratios at 750 ppm (**c**), and single and mixture of extracts at 750 ppm (**d**). presented in Figure 4:0 The table shows that the deviation of experimental and theoretical values is not significant at both standard values. In this case, the maximum deviation values for causal factors 2 and 3 were 9% and 7%, respectively. Moreover, the current density was significantly reduced by increasing the extract concentration.