## 3 Results and Discussion
### Polarization Measurements  
As it was demonstrated in the SEM images above, the presence of the film on the surface of the magnesium electrode was being observed from the first minutes of corrosion, also affecting its electrochemical behavior.  
First of all, it was manifested in the displacement of the potential of the magnesium electrode in time to the positive side (Table 2), which characterizes the passivation of the surface with a corrosion film.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\tau\), min & 0.5 mol/L Na\({}_{2}\)SO\({}_{4}\) & 0.5 mol/L MgO\({}_{4}\) & 1 mol/L MgO\({}_{4}\) & 2 mol/L MgO\({}_{4}\) \\ \hline
1 & 1.68 & 1.52 & 1.72 & 1.89 \\
5 & 1.65 & 1.56 & 1.67 & 1.80 \\
10 & 1.63 & 1.66 & 1.63 & 1.74 \\
20 & 1.68 & 1.63 & 1.73 & 1.72 \\
30 & 1.62 & 1.48 & 1.65 & 1.70 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Potential of the magnesium electrode (V) versus to the Ag/AgCl electrode in the first half hour of corrosion in different electrolytes.  
Figure 3: Morphologies of the magnesium electrode surface at different immersion time in 0.5 mol/L Na\({}_{2}\)SO\({}_{4}\) solution: (**a**) 0 min, (**b**) 1 min, (**c**) 5 min, (**d**) 10 min, (**e**) 20 min, and (**f**) 30 min.  
The exception was a negative shift in the first 15 min of the magnesium potential of 0.5 mol/L MgSO\({}_{4}\). This coincides with the trend of increasing film cracking in the time interval up to 10 min (Figure 1). Shifting the magnesium potential in magnesium sulfate solutions to the negative side also indicates less passivity due to the formation of looser films.  
The anode polarization curves on magnesium possessed the form of exponent for sodium sulfate solutions with output to the limit current for magnesium sulfate solutions. Cathode curves possessed a less expressed current boost, although in the Tafel's coordinates both anode and cathode branches were well rectified (Figures 4 and 5).  
Concurrently, dependence of the potential-logarithm current consists of two or even three sites for anode polarization in magnesium sulfate solution. The first site from the stationary potential to 20-40 mV overvoltage has deviation from linear dependence, connected with distortion of partial polarization curve by corrosion process in the area of compromise potential. Deviations from linear dependence for the anode process in magnesium sulfate (Figure 5a) at more positive potentials are most likely due to salt anode passivation. The absence of such passivation in sodium sulfate solutions is due to the greater solubility of the anode dissolution product (magnesium hydroxide) in these solutions [29] in comparison with magnesium sulfate solutions. Hydroxide is formed in the anode process due to monovalent magnesium [14].  
The Tafel's coefficients and polarization resistances were calculated according to polarization curves at different immersion time of the electrode in the tested solutions.  
Figure 4: Anode (**a**) and cathode (**b**) polarization curves on the magnesium electrode in 0.5 mol/L Na\({}_{2}\)SO\({}_{4}\) solution after different immersion times, \(\upsilon=10\) mV/s.  
Figure 5: Anode (**a**) and cathode (**b**) polarization curves on the magnesium electrode in 0.5 mol/L MgSO\({}_{4}\) solution after different immersion times, \(\upsilon=10\) mV/s; sidebar: in semilogarithmic coordinates.