Abstract
In this article, the results of studying the polarization characteristics of magnesium covered with corrosion film in aqueous solutions of MgSO4 and Na2SO4 are presented. The absence of a corrosion-free magnesium surface was shown; in this connection, it was proposed to interpret the larger values of Tafel’s coefficients obtained in the experiment from the point of view of limiting the electrochemical process by charge transfer in the film phase. Charge transfer in corrosion films obeys the regularities of particle movement in high electric fields, and it is not only cationic. According to the impedance measurements, the resistance of the oxide and hydroxide layer of the magnesium-based corrosion film in the studied solutions was calculated. The largest contribution to the restriction of charge transfer in the initial stages of corrosion is made by a dense primary film defining the polarization resistance. Correlation of transfer parameters in high electric fields with thickness and resistance of corrosion film was demonstrated.
Highlights
The wide application of magnesium is limited by its low corrosion resistance
1/b for almost all the and stabilization of the film resistance on magnesium in magnesium and sodium sulfate solutions curves except anode ones in sodium sulfate solutions in the first half hour of corrosion presented itself after 100 min of corrosion attracts itself the attention, when the rates of their change are markedly the curve a parabolic dependence, due toare thisconverged, we presented these curves ina1/b to t coordinates slowed downof and the values themselves demonstrating movement towards (Figure 6b) independence from the nature of the electrolyte
Analysis of the polarization dependences of the magnesium electrode, which is corrosive in sodium and magnesium sulfate solutions, makes it possible to conclude that the limiting stage of the electrochemical process is the transfer of charge through the corrosive film
Summary
The wide application of magnesium is limited by its low corrosion resistance. During the last decade, many researches have focused on the effect of the metal microstructure and medium on the magnesium corrosion behavior [1,2,3,4]. In many works [3,4,5,12,16,21,22,24,25], the corrosion film on magnesium in different solutions is presented as a two-layered one It consists of a thin dense layer of the MgO adjacent to metal and friable hydroxide on its surface, at the same time oxide is the main barrier layer. Excess of the corrosion current calculated from polarization measurements over currents from volumetric measurements is referred to anode dissolution in the form of monovalent magnesium ion For this reason, the authors recommend investigating the possibility of applying the method of determining corrosion characteristics by polarization dependencies to magnesium very carefully. In connection with the above-mentioned, all the electrochemical measurements were interpreted considering the role of surface corrosion films in charge transfer processes with an appropriate analysis of the regularities of the charge transfer through the phase of corrosion products on the surface
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