## 3 Results and Discussion
### Morphology Evaluation
It can be seen that the surface of mild steel without the influence of inhibitors has lots of corrosion signs, as it is the bluish gray stain, indicating that uniform and local corrosion phenomena took place, with an accelerated rate regarding to the blank system (_Steel-NaCl-blank_, Figure 1e). On the other hand, corrosion products are also observed on the surface of both _Steel-NaCl-Na2 HPO4_ and _Steel-NaCl-MBT_ (Figure 1f,g), reassuring that the chosen inhibitors are appropriate for the present system. Moreover, the surface of the sample with the presence of both inhibitors seems free from corrosion products in the outer area and a more compact, dark-colored adherent layer onto the metallic surface was developed, with brown-gray color, which was probably brown due to the organic tail of MBT and blackish/gray due to magnetite and/or wustite compounds, as will be discussed below (_Steel-NaCl-Na2 HPO4-MBT_, Figure 1h) [45]. The SEM images of mild steel prior to exposure to electrolytes (_Steel-blank_) are illustrated in Figure 2. It can be seen that there are holes, dents, and scratches on the surface either due to the fabrication of the specimens or due to the cleaning process. Taking into account the EDS analysis, the iron value concentration was measured to be approximately 92.9 wt %, while the corresponding  
Figure 1: Visual images of mild steel after submission for 96 h: in WSS (**a**) _Steel–WSS–blank_, (**b**) _Steel–WSS–Na2 HPO4_, (**c**) _Steel–WSS–MBT_, (**d**) _Steel–WSS–Na2 HPO4–MBT_; in 3.5 wt % NaCl (**e**) _Steel–NaCl-blank_, (**f**) _Steel–NaCl–Na2 HPO4_, (**g**) _Steel–NaCl–MBT_, (**h**) _Steel–NaCl–Na2 HPO4_–MBT_. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Spectrum at**} & \multicolumn{8}{c}{**wt \% Element Concentration**} \\ \cline{3-8}  & & **O** & **Fe** & **C** & **Si** & **P** & **S** & **Na** \\ \hline _Steel–blank_ & Figure 2a & 0.1 & 92.9 & 3.7 & 2.0 & - & - & - \\ _Steel–WSS–blank_ & Figure 3b & 52.3 & 44.0 & 1.5 & 2.3 & - & - & - \\ _Steel–WSS–Na\({}_{2}\)HPO\({}_{4}\)_ & Figure 4b & 39.9 & 39.5 & 2.6 & 0.2 & 14.2 & - & 2.4 \\ _Steel–WSS–Na\({}_{2}\)HPO\({}_{4}\)_ & Figure 4f & 16.9 & 72.4 & 3.0 & 1.7 & 2.7 & - & 2.3 \\ _Steel–WSS–MBT_ & Figure 5e & 44.6 & 46.1 & 4.2 & 1.2 & - & 3.6 & - \\ _Steel–WSS–MBT_ & Figure 5f & 44.4 & 46.9 & 4.3 & 1.5 & - & 2.9 & - \\ _Steel–WSS–Na\({}_{2}\)HPO\({}_{4}\)–MBT_ & Figure 6c & 31.2 & 40.0 & 7.8 & 0.4 & 11.3 & 3.6 & 2.6 \\ _Steel–NaCl–Blank_ & Figure 7e & 61.3 & 38.7 & - & - & - & - & - \\ _Steel–NaCl–Na\({}_{2}\)HPO\({}_{4}\)_ & Figure 8b & 39.3 & 39.0 & 3.0 & 0.3 & 14.9 & - & - \\ _Steel–NaCl–MBT_ & Figure 8d & 35.5 & 49.9 & 3.3 & 0.1 & 6.5 & - & 3.0 \\ _Steel–NaCl–MBT_ & Figure 9b & 23.0 & 67.4 & 4.7 & 1.5 & - & 2.2 & - \\ _Steel–NaCl–Na\({}_{2}\)HPO\({}_{4}\)–MBT_ & Figure 10b & 47.1 & 26.8 & 4.5 & - & 16.0 & 5.2 & 0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Tabulated values of wt % element concentration of mild steel panels prior and after subjection in either WSS, or 3.5 wt % NaCl for 96 h in the presence of inhibitors or not. Figure 5: SEM images of mild steel immersed in WSS for 96 h in the presence of MBT. Figure 6: SEM images of mild steel immersed in WSS for 96 h in the presence of Na\({}_{2}\)HPO\({}_{4}\) and 2-mercaptoethanolobenzothiazzoole (MBT). In general, the surface characterization of mild steel corrosion products remains a quite demanding issue, as denoted by previous works [46]. Various image analyzing techniques were deployed in order to assess the mild steel surface relating to its corrosion products structure and behavior after immersion in the studied inhibitor solutions. Figure 8: SEM images of mild steel immersed in 3.5 wt % NaCl for 96 h in the presence of Na\({}_{2}\)HPO\({}_{4}\). Figure 7: SEM images of mild steel immersed in 3.5 wt % NaCl for 96 h in the absence of inhibitors. Figure 9: SEM images of mild steel immersed in 3.5 wt % NaCl for 96 h in the presence of MBT.