## 3 Results and Discussion
### Corrosion Inhibition Mechanism
#### 3.5.1 The Main Pathway of Corrosion Process in an Fe-C/NaCl (aq) System  
Taking into account the mild steel submission in the saline solution, a milestone for the initiation of corrosion could be considered the time when the first ferrous ions (Fe\({}^{2+}\)) or ferric ions (Fe\({}^{3+}\)) ions release (Reactions 5 and 6), defining the anodic site that emerges near the metallic surface. Subsequently, the local charge density increases, causing the appearance of the cathodic current, and taking into account that the pH of the electrolytic solutions was in a range from 7.33 to 7.97, the dissolved O\({}_{2}\) reacts with H\({}_{2}\)O and becomes reduced to OH\({}^{-}\) ions (Reaction 7). In the same way, as in the case of mild steel, the alloying elements release Mn\({}^{2+}\), Cu\({}^{2+}\), and other cations, originating from the dissolution of the alloy equally to Fe oxidation and maintaining the stoichiometric ratio they used to have in the alloy. The consequent excess either of Fe\({}^{2+}\) or Fe\({}^{3+}\) and OH\({}^{-}\) of the main oxidation-reduction reactions (8, 9) results in the precipitation of iron hydroxides from the solution to the corroded surface. \[\mathrm{Fe}\rightarrow\mathrm{Fe}^{2+}+2\mathrm{e}^{-},\mathrm{a}\mathrm{a} \mathrm{o}\mathrm{o}\mathrm{o}\mathrm{o}\mathrm{  
corrosion phenomena, local physicochemical conditions (pH, ions concentration etc.) and physical parameters such as the humidity or aeration level of the surface.  
Consequently, charge separation takes place and signals the start of the second phase of the corrosion mechanism on a mild steel surface, according to the [PERSON] model perspective. As mentioned, in anodic areas, Fe(OH)\({}_{2}\) and Fe(OH)\({}_{3}\) create a characteristic thick gel that restricts the diffusion of the products of reduction semi-reactions such as O\({}_{2}\) and OH\({}^{-}\), which are usually responsible for the rust layer deterioration at a later stage. Additionally, Cl\({}^{-}\), which originates in the NaCl(aq) solution and the soluble forming Fe-Cl salts ionization (reactions 10, 11), since they are more reactive than OH\({}^{-}\), they tend to attack the protective layer, reacting with the agile Fe\({}^{2+}\) of the anodic dissolution, triggering a series of local corrosion phenomena, which would open the way even to reach and hazard the inner layer (reactions 12, 13). For example, in wet conditions, the chemical reactions (5) and (14) occur, indicatively:  
\[\mathrm{Fe}^{+2}+2\mathrm{Cl}^{-}\rightarrow\mathrm{FeCl}_{2}, \tag{10}\]  
\[\mathrm{Fe}^{+3}+3\mathrm{Cl}^{-}\rightarrow\mathrm{FeCl}_{3}, \tag{11}\]  
\[\mathrm{FeCl}_{2}+2\mathrm{H}_{2}\mathrm{O}^{-}\rightarrow\mathrm{Fe(OH)}_{2 }(\mathrm{s})+2\mathrm{HCl}, \tag{12}\]  
\[\mathrm{FeCl}_{3}+3\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{Fe(OH)}_{3}( \mathrm{s})+3\mathrm{HCl}, \tag{13}\]  
\[\mathrm{8 FeOOH}+\mathrm{Fe}^{2+}+2\mathrm{e}^{-}\rightarrow\mathrm{3 Fe_{3}O _{4}}+4\mathrm{H}_{2}\mathrm{O}, \tag{14}\]  
After a relative stabilization of the primary ablation processes and iron oxides and hydroxides interaction, the eventually generated [Fe-O-OH] thick gel, which is chemically attached to the inner layer of corrosion products, obtains a unique for each system constitution of crystalline iron oxide phases. This constitution depends on the Fe\({}^{2+}\), Fe\({}^{3+}\), and dissolved O\({}_{2}\), OH\({}^{-}\) availability, the mixture of which is responsible for the emergence of a pioneering family of materials, the layered double hydroxides (LDH) [90,91], with green rust as the main representatives in literature [92,93]. Taking into account that the direct oxidation of iron or low-alloyed steel to the unstable ferric ions (Fe\({}^{3+}\)) is restricted thermodynamically against the generation of ferrous ions (Fe\({}^{2+}\)), it could be assumed that the concentration of the former would be found to be negligible, referring to the whole rust layer structure.