Anodic and cathodic polarizations of nickel have been studied using a galvanostatic technique with low current densities and an atmosphere of hydrogen. Polarization experiments have been conducted using 0.1 N sodium hydroxide, 1 N sodium carbonate and 0.1 N sodium borate solutions. It has been shown that passivation is caused by the formation of a monomolecular layer of Ni(OH)2 in alkaline solutions and by 1-2 molecular layers in borate solution. On further oxidation, the Ni(OH)2 becomes oxidized to Ni2O3 and finally to a nonstoichiometric oxide corresponding to NiO1.8. This final oxidation state is unstable and decomposes as soon as the electrode is made cathodic. It has been shown that current density has a critical effect on polarization characteristics in the borate solution. No evidence was found for the existence of the intermediate oxide Ni3O4.

Subject
Anode potential, Sodium carbonate, Cathodic potential, Oxides, Borate, Alkaline solutions, Sodium, Oxygen, Nickel, Electrodes, Electrode potential, Oxidation, Critical anodic current density
© 1964 National Association of Corrosion Engineers
1964
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