ANODIC BEHAVIOUR OF COBALT IN ALKALINE SOLUTIONS

The anodic polarization of cobalt in sodium hydroxide solutions has been studied under potentiostatic and galvanostatic conditions. Only two stages in the oxidation were found. It is suggested that these correspond to the transitions Co/Co(OH)2 and Co(OH)2/Co(OH)3. The nucleation and growth of the passivating layer of cobaltous hydroxide is discussed by analysis of the current/time curves at various constant potentials. The results of the present studies have shown that the oxidation of a clean cobalt surface takes place in two stages. This is supported by both potentiostatic and galvanostatic experiments, and in no case was a significant third process found between the rest potential and the point of oxygen evolution. The two oxidation stages are attributed to the transitions Co → Co(OH)2 and Co(OH)2 → CoOOH, The current/time curves show that in 1 N NaOH the passivating layer grows in three dimensions (on the simple model, hemispherical growth being assumed), and that progressive nucleation occurs. From the analysis of these curves, a simple mechanism for growth is proposed. © 1969.