## 3 Results and Discussion
### Electrochemical Studies  
All the EIS, PP, and LPR electrochemical characterizations were performed in a pH range from 7.33 to 7.97 (Table 2). It should be taken into consideration that all the electrochemical measurements were conducted in triplicate, and a corresponding representative curve is illustrated for each sample. In general, the presence of a compound into an electrolyte solution can shift the OCP either into positive values if the compound reacts as an anodic inhibitor retarding the oxidation process, or into negative values if the compound inhibits the cathodic reactions. The observation of the OCP values in respect of the time can provide information related to the stability of the electrolytic system in order for linear sweep voltammetry characterizations such as PP to be conducted. Taking into account the evolution of OCP versus time in the case of mild steel panels after subjection in WSS for 23 h at room temperature (Figure 15), it is observed that the system including the mild steel together with the phosphates (_Steel-WSS-Na2 HPO4_) shifts the OCP to more positive values after the fourth hour compared to the one of the _Steel-WSS-blank_. This indication clearly denotes that Na2 HPO4 acts as an anodic inhibitor for mild steel, which is a result that is also confirmed by the literature [75]. On the other hand, for the system _Steel-WSS-MBT_, the OCP shifts to negative values, indicating that the presence of MBT inhibits the cathodic reactions [76]. Finally, the presence of both Na2 HPO4 and MBT into the WSS (_Steel-WSS-Na2 HPO4_-MBT_) results in OCP values more negative  
Figure 14: XRD spectra of the mild steel panels after submission in 3.5 wt % NaCl for 96 h: (**a**) _Steel–NaCl–blank_, (**b**) _Steel–NaCl–Na2 HPO4_, (**c**) _Steel–NaCl–MBT_, (**d**) _Steel–NaCl–Na2 HPO4_–MBT_. Figure 13: XRD spectra of the mild steel panels after submission in WSS for 96 h: (**a**) _Steel–WSS–blank_, (**b**) _Steel–WSS–Na2 HPO4_, (**c**) _Steel–WSS–MBT_, (**d**) _Steel–WSS–Na2 HPO4_–MBT_. than those of _Steel-WSS-blank_ and more positive than those of _Steel-WSS-MBT_. This behavior can be assigned to the simultaneous inhibition of the cathodic reactions as well as to the formation of a protective layer that inhibits the anodic reactions. Moreover, it can be mentioned that during the beginning of exposure (0-2 h), the corrosion potential (OCP) is lower than in isolated inhibitor systems due to passivation, but as the exposure time elapses, the OCP increases up to an almost stable moderate value for many hours. This behavior is characteristic of the accelerated formation of metastable pits at first and the gradual passivation of all of them, up to the restoration of the passive layer and the return of the system to the initial OCP, which is a process known as re-passivation [77]. Considering the evolution of OCP versus time in the case of the mild steel panels after subjection in 3.5 wt % NaCl for 23 h at room temperature (Figure 16), it can be noticed that the presence of Na\({}_{2}\)HPO\({}_{4}\) and MBT in the electrolytic solutions increases the OCP compared to the _Steel-NaCl-blank_. These facts denote that there is an inhibition to the anodic reactions resulting in the corrosion protection of the mild steel. The increase in potential is assigned to the creation of protective films onto the metal surface, making it more resistant to corrosion than the panel subjected to the solution without inhibitor additives. Moreover, it may be remarked that MBT acts as a mixed inhibitor for mild steel in NaCl solutions [78]. Figure 16: The evolution of OCP versus time in case of the mild steel panels after submission in 3.5 wt % NaCl for 23 h: (**filled square**) _Steel–NaCl–blank_, (**filled circle**) _Steel–NaCl–Na\({}_{2}\)HPO\({}_{4}\)_, (**filled triangle**) _Steel–NaCl–MBT_, (**filled triangle**) _Steel–NaCl–Na\({}_{2}\)HPO\({}_{4}\)–MBT_.