## 3 Results and Discussion
### Analysis of the Laws of Charge Transfer during Polarization
In most cases, the Tafel's coefficient was higher than 200 mV, except for the initial stage of corrosion in 0.5 mol/L magnesium sulfate solution at anode polarization. In the anode process in magnesium sulfate at early terms, the Tafel's coefficient has a value close to 60 mV, formally corresponding to one-electron transfer. However, its completely smooth change to 0.3V in 200 min indicates that this is a characteristic of a growing corrosion film. Accordingly, the Tafel's coefficient being determined here is 1/_b_ value for transport in high electric fields, and it reflects the thickness of the corrosion film according to Equation (5). In sodium sulfate solutions, the Tafel's coefficient was higher from the very outset of the corrosion process for both the anode and cathode processes. The change in the value of 1/_b_ for almost all the curves except anode ones in sodium sulfate solutions in the first half hour of corrosion presented itself the curve of a parabolic dependence, due to this we presented these curves in 1/_b_ to 1/2 coordinates (Figure 6b)  
Such parabolic dependences were often observed when measuring the amount of released hydrogen, as it was reported in [12]. In [22], a quantitative implementation of the parabolic law was  
Figure 6: Dependence of 1/_b_ (**a,b**), polarization resistance (\(R_{p}\)) (**c**), and corrosion potential (\(E\)) (**d**) on the immersion time of the electrode in various electrolytes. established for the dependence of the magnesium hydroxide content on time. The parabolic law itself reflects the corrosion process, which is limited by diffusion of the reagent through the thickness \(L\) of the growing product layer according to equation \(L\ =\ \left(L_{0}^{2}+\pi\right)^{\frac{1}{2}}\)[18]. Here, \(L_{0}\) is the initial film thickness and \(\tau\) is the corrosion time. In these curves, the Tafel's coefficient change (1/_b_) was linear in time at the initial regions of \(\sim\)30 min, except of the dependence for the cathode coefficient in magnesium sulfate having a linear site till 4 h of corrosion. Simultaneously, at all linear sites in these coordinates the periodic deviations in both sites of the straight line were observed. Comparison of emerging deviations with film behavior by microscopic studies showed that they most likely corresponded to cracking and growth of cracks in the film, as well as hydrogen evolution, when parameters of charge transfer through it could change dramatically due to such effects. The rectification of the dependence in coordinates 1/_b_ - \(\tau^{1/2}\) indicated that the corrosion process was limited by diffusion of the reagent through the thickness of the growing product layer. The diffusion model underlying the parabolic law of the film growth was the diffusion of metal magnesium in ion-electron form through a layer of corrosion products to the electrolyte. This motion first happened in the primary magnesium oxide film, on the surface of which the electron reacted with water to hydrogen evolution. In the solid phase of magnesium oxide, monovalent magnesium was most likely formed, which was also a reducing agent providing hole conductivity and reacting with water to hydrogen evolution. The existence of monovalent magnesium as a reducing agent in the hydroxide layer was impossible, as well as electron conductivity. The observed difference of the Tafel's characteristics for the anode and cathode process was apparently determined by the nature of the particle transferred through the film, which, in accordance with Equation (6), determined the b value. In the cathode process, it was an electron being carried from the metal through the film to the solution and a magnesium cation moving in the reverse direction, whereas in the anode process, only the cation was being carried. Based on the data of the NDE study, it may be assumed that it was a single-charged magnesium cation.