Anodic dissolution of cobalt in sulfate electrolyte

• Е.А. Eliseeva¹, S.L. Berezina¹, L.G. Goritchev² and O.N. Plakhotnaya³

¹ Bauman Moscow State Technical University, 2-nd Baumanskaya str., 5, 105005 Moscow, Russian Federation
² Moscow Pedagogical State University, 1/1 Malaya Pirogovskaya str., 119991 Moscow, Russian Federation
³ First Moscow State Medical University named after I.M. Sechenov, Trubetskaya str., 8, 119991 Moscow, Russian Federation

Abstract: This paper presents the results of studying the anodic behavior of cobalt in an aqueous electrolyte based on sodium sulfate in a wide pH range. Anodic curves obtained in the potentiostatic mode show regions of active dissolution and regions of transition to the passive state. It has been found that a change in the pH of the medium has different effects on the activation of the anodic process, while the general character of the polarization curves does not change. Differences in the values of the equilibrium potentials of cobalt, the potentials of active dissolution, and the limiting density of the anodic current were revealed. The most pronounced dependence is observed in the range of pH 2–6 and pH 11–15. It has been shown that the active dissolution of cobalt is due to ionization processes, while the passive state is determined by the composition of the surface oxide film. Based on experimental and thermodynamic data, it has been concluded that anodic oxidation occurs in stages with formation of intermediate valence compounds, and a scheme for the anodic dissolution mechanism has been suggested. It has been noted that electrode passivation in the region of active-passive transitions is due to the formation of surface compounds from CoOOH to CoO₂ with formation of intermediate oxide phases. The data obtained enrich the understanding of the electrochemistry of cobalt and may be relevant in the development of corrosion inhibitors for cobalt-containing alloys.

Keywords: cobalt, electrode potential, polarization curves, anodic dissolution, current density

Int. J. Corros. Scale Inhib., 2022, 11, no. 1, 151-160
doi: 10.17675/2305-6894-2022-11-1-8

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