## 3 Results and Discussion
### Raman Spectroscopy Analysis
Hence, the initial expected peaks of iron oxides and oxyhydroxides [67] are distorted due to the voluminous amorphous compounds. An intense peak at 1319 cm\({}^{-1}\)[63] is attributed to hematite (\(\alpha\)-Fe2O3) and the less intense peak at 1593 cm\({}^{-1}\)[46] is attributed to (2-line) ferrihydrite (Fe5 HO8-4H2O), which makes its appearance between 1380 cm\({}^{-1}\) and 1600 cm\({}^{-1}\)[7]. Taking into account the Raman spectrum of _Steel-NaCl-Na2 HPO4_ (Figure 12b), it may be remarked that the absence of a peak near 218-221 cm\({}^{-1}\), which is attributed in the literature to the symmetric stretch of interlayer chloride ions in green rust [63; 68] in combination with the detection of iron  
Figure 12: Raman spectra of the mild steel panels after injection 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_. phosphate salts vibrations, at 430-450 cm\({}^{-1}\) for Fe\({}_{4}\)(P\({}_{2}\)O\({}_{7}\))\({}_{3}\) and at 1011 cm\({}^{-1}\) for a symmetric PO\({}_{3}\)[2]-symmetric stretch of Fe\({}_{3}\)(PO\({}_{4}\))\({}_{2}\)A (A for anion) [69], reassures mild steel surface phosphating and consequently the increase of crystallinity in corrosion products after exposure and drying processes. Considering the _Steel-NaCl-MBT_ (Figure 12c), it can be noticed that although low wavenumbers of Raman shift are connected with iron oxides as commented, the differentiation of mild steel spectrum enhances the surmise of MBT physical and chemical adsorption, which is in accordance with the absence of other characteristic peaks of MBT, as at 717 cm\({}^{-1}\), 1013 cm\({}^{-1}\), 1564 cm\({}^{-1}\), and 1593 cm\({}^{-1}\). The strongest peak near 278 cm\({}^{-1}\) in conjunction with noisy, less intense peaks at 350 cm\({}^{-1}\), 470-480 cm\({}^{-1}\), 530-540 cm\({}^{-1}\), and 610 cm\({}^{-1}\) reveal the generation of the Fe-S bond [71]. A less intense but relatively obvious peak obtained near 1320 cm\({}^{-1}\) is connected to the N = C-S ring stretching mode, with its intensity considered in the literature as proportionate to the inhibitor chemisorption progress [71]. The peak at 1395 cm\({}^{-1}\) is considered to stem from stretching vibrations of the C-C band in the aromatic ring of MBT [65]. In view of the _Steel-NaCl-Na\({}_{2}\)HPO\({}_{4}\)-MBT_ (Figure 12d), it can be said that a more clarifying Raman spectrum with more than 15 Raman shift peaks was gained under accelerating corrosion conditions, as there are in the saline solution. The smaller peaks near 300 cm\({}^{-1}\) (shoulder) and 400 cm\({}^{-1}\) in addition to those near 500 cm\({}^{-1}\) and 530 cm\({}^{-1}\) are assumed to be caused by Fe-S generated by the chemisorption of MBT on the surface of the sample [71]. The peak that arises near 700 cm\({}^{-1}\) may be attributed to P-O-P symmetric stretch vibrations, taking into account the simultaneous appearance of a smaller peak near 850 cm\({}^{-1}\) generated by [HPO\({}_{4}\)]\({}^{-2}\) anion symmetric stretch [54; 63]. The next pair of Raman shifts near 1000 cm\({}^{-1}\) (shoulder) and 1120 cm\({}^{-1}\) comes to identify iron phosphate crystalline or amorphous phases [69] in conjunction with the combination of two other shifts near 1250 cm\({}^{-1}\) and 1270 cm\({}^{-1}\) and a smaller shift at 1310 cm\({}^{-1}\), the latter of which may have been gained from PO\({}_{2}\) asymmetric stretch. Moreover, the pair of 1430 cm\({}^{-1}\) and 1480 cm\({}^{-1}\) peaks in combination with those at 1580 cm\({}^{-1}\) and 1590 cm\({}^{-1}\) were noted to be in accordance with experimental Raman shift values for the adsorbed MBT molecule, especially when it is measured in its thione mode [65; 72].