## 3 Results and Discussion  
### Morphology Evaluation  
The visual pictures of mild steel immersed in WSS for 96 h, in the presence of inhibitors or not, are demonstrated in Figure 1a-d. Onto the slightly rinsed corroded surface of Figure 1a, ferrous yellowish, orange, and brownish red species create a hardly homogenous layer, as expected from the literature for the mild steel surface in the absence of inhibitors (_Steel-WSS-blank_). Susceptible to a series of local corrosion phenomena as well as to the creation of local galvanic cells and pits, the final layer emerges in dependence with the local composition and physicochemical conditions of the system [44]. In depth, it is claimed that reddish hues stem from hematite (\(\alpha\)-Fe2O3) in a hexagonal crystal system, in which the face-sharing octahedral keeps the Fe centers at the shortest distance (0.29 nm), whereas the yellowish ones are caused by the edge- or/and corner-sharing octahedral of lepidocrotic [\(\gamma\)-FeO(OH)], maghemite (\(\gamma\)-Fe2O3), goethite [\(\alpha\)-FeO(OH)] and other compounds, with Fe center distances from 0.30 to 0.35 nm. In the presence of each inhibitor separately, the mild steel surface is either converted by the phosphate invasion into the crystal lattice, in case of phosphate solution in _Steel-WSS-Na2 HPO4_ (Figure 1b), or covered by the organic three-dimensional organic layer precipitated, in the case of MBT in _Steel-WSS-MBT_ (Figure 1c). In mere phosphate solutions, the lack of reddish corrosion products and the development of a thinner and yellower final layer, as shown in Figure 1b (_Steel-WSS-Na2 HPO4_) \begin{table}
\begin{tabular}{c c c} \hline
**Composition** & **pH** & **Sample** \\ \hline - & - & _Steel–blank_ \\ WSS & 7.41–7.52 & _Steel–WSS–blank_ \\ WSS + 0.849 g/L Na2 HPO4 & 7.78–7.97 & _Steel–WSS–Na2 HPO4_ \\ WSS + 1.014 g/L MBT & 7.33–7.52 & _Steel–WSS–MBT_ \\ WSS + 0.849 g/L Na2 HPO4 + 1.014 g/L MBT & 7.38–7.82 & _Steel–WSS–Na2 HPO4-MBT_ \\ NaCl 3.5 wt \% & 7.71–7.72 & _Steel–NaCl–blank_ \\ NaCl 3.5 wt \% + 0.849 g/L Na2 HPO4 & 7.78–7.97 & _Steel–NaCl–Na2 HPO4_ \\ NaCl 3.5 wt \% + 1.014 g/L MBT & 7.33–7.52 & _Steel–NaCl–MBT_ \\ NaCl 3.5 wt \% + 0.849 g/L Na2 HPO4 + 1.014 g/L MBT & 7.38–7.82 & _Steel–NaCl–Na2 HPO4-MBT_ \\ \hline \end{tabular}
\end{table} 
Table 2: Composition of the solutions for testing the effectiveness of the inhibitors onto mild steel. Reagents concentration 6 mM, reagents solubility in water (mg/100 g, 20 \({}^{\circ}\)C) \(1.7\times 10^{3}\) Na2 HPO4, \(1.9\times 10^{1}\) MBT. and Figure 1f (_Steel-NaCl-Na2 HPO4_), are characteristic of the corrosion process due to the hindrance of hematite formation, as detailed below. Since the earlier stages and according to the literature, the inner layer (2D layer) is expected to consist of gray and blackish magnetite (Fe3O4) and maybe wustite (FeO). Supplementary to the electrochemical and spectroscopic measurement analyses that are discussed in detail below, the visual image of Figure 1d confirms the synergistic action of the inhibitors (_Steel-WSS-Na2 HPO4-MBT_), overcoming the defects and enhancing the advantages of the preceded separate use of MBT and Na2 HPO4. After the exposure tests, a compact, resistant, uniform, protective layer was created, appearing to have a light-colored saline coating in the outer and a metallic gray or blackish inner layer, which is the magnetite layer. At a first glance, the lack of brown, reddish, and yellowish hues in the corrosion products incline us toward the conception that the main and more time-consuming corrosion processes were restricted successfully, resulting in a resistant and adherent protective layer on mild steel, which was almost intact after 96 h of subjection in a slightly saline environment and even after drying. The mild steel visual pictures after exposure to 3.5 wt % NaCl for 96 h, in the presence or absence of inhibitors, are illustrated in Figure 1e-h.