## 3 Results and Discussion
### Morphology Evaluation
In order to extract as much information as possible, it is a prerequisite to adopt a circumstantial model for the mild steel surface corrosion system during subjection in aquatic solutions, such as those proposed in the literature [7, 47]. It is commonly accepted that the initial mixture of corrosion products consists of a primary viscous layer on a mild steel surface, to undergo afterwards gradation and separation into two distinguishable layers (an electrochemical double layer), an adherent rust layer, and a loosely adherent anodic oxide film [3, 48]. At an early stage, amorphous masses of oxides with a spongy appearance are created, to transform primarily to lepidocrocite, part of which is further transformed in goethite. The studied phases have been generated either from the direct precipitation from a ferrous or a ferric solution, or by transformation of another iron oxide, at room temperature [3, 49]. At a first glance at preceding investigations, [PERSON]'s model [50] regarding phase transition during wetting and drying conditions could contribute to illustrating the expended phase composition of a mild steel surface, after the prolonged exposure tests [51]. Consequently, during exposure, the reduction of lepidocrocite to a hydrated Fe\({}^{2+}\)- intermediate takes place (phenomenon ofolation) due to metal anodic dissolution, especially near the steel surface, where magnetite appears. However, oxidizing reactions can result in the emergent of lepidocrocite and maghemite phases [1, 50, 51] when oxygen circulation is evitable by drying [7]. The SEM images of mild steel immersed in WSS (_Steel-WSS-blank_) for 96 h, in the absence of inhibitors, are illustrated in Figure 3. Characteristic laminar morphologies of lepidocrocite were captured on the reference sample surface, exhibiting a large spectrum of more or less known crystalline formations, as it is denoted in the literature. Near the mild steel surface broken glass type [3], flowery and worm nest shapes dominate, in parallel with the gradual growth of miscellaneous laminar volumes of lepidocrocite formed radially outward from the metal surface. This particular formation is also described by many as cotton balls [3] and defined as crystalline phases due to the aggregation of flat grains of lepidocrocite grown on top of amorphous \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\).H\({}_{2}\)O [46, 48]. The EDS analysis of Figure 3b discloses enhanced oxygen value concentration compared to that of the _Steel-blank_ sample due to the creation of the aforementioned iron oxides (Table 3). The surface SEM images of _Steel-WSS-Na\({}_{2}\)HPO\({}_{4}\)_ after subjection in WSS for 96 h are depicted in Figure 4. It can be seen that characteristic tassel-like structures, mainly consisting of [FeII-OH] compounds, with substituted hydroxyls by phosphate anions (H\({}_{2}\)PO\({}_{4}\)\({}^{-}\), HPO\({}_{4}\)\({}^{3-}\)) [52], reveal the phosphates incorporation, thus making possible the identification of iron phosphates, appearing in amorphous or crystal phases. The latter are often observed as filamentous agglomerates [53] (Figure 4a,b). However, phosphorous detection through microscopy techniques of EDS analysis of the surface has been considered harsh, as phosphate anions get incorporated in steel crystal lattice [26]. Furthermore, ordinary structures of lepidocrocite spongy structure (and probably parts of maghemite, a phase that usually adopts the shape of its precursor [54]) and smaller aggregations of magnetite (as more globular, smooth) seem to be present, while a compact continuous inner layer (with cracks from drying process) has been obviously generated, which is indicative of steel surface passivation by phosphates (Figure 4c,d). In addition, large platy crystals of nanocrystalline phases are captured, reassuring the creation of the expected thin adherent passive layer of iron phosphates, maghemite, and lepidocrocite in crystalline and amorphous formations [26, 53] (Figure 4e,f).