On some characteristics of cathodic processes in nickel electrodeposition

✍ Scribed by J. Matulis; R. Sližys

• Publisher: Elsevier Science
• Year: 1964
• Tongue: English
• Weight: 828 KB
• Volume: 9
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(64)85009-x

✦ Synopsis

The potential of Ni2+-ion discharge at room temperature at first rapidly rises with an increase in pH of the solution, then within the pH range from 3.5 to 4.5 it decreases sharply, whereupon it again gradually begins to rise.

Similar potential changes with an increase in pH are observed also in the case of a non-polarized electrode.

For instance, the open-circuit potential of nickel in solutions of sulphuric acid and potassium sulphate rises linearly with an increase in pH to ca 3.5. Within the pH range from 3.5 to 4.7 the open-circuit potential changes considerably and its reproducibility is impaired. When the solution is made more alkaline within the pH range from 4.7 to ca 7.0, the increase in the potential becomes linear.

By accurate measurements of pH in the vicinity of the cathode surface, it has been established that the changes in the potential of both non-polarized and polarized nickel electrodes observed are due to the regular changes in the acidity of the solution in the layer near the cathode.

1 min after the immersion of a nickel electrode into the solution, the ApH in the vicinity of the electrode surface rises from 0.0 to 2.5, depending on the acidity of the medium. Upon cathodic polarization, pH rises to 7-8. But within the pH range from 3.5 to 4.5 an arrest in its increase is observed. The stepwise change in pH in the vicinity of the electrode surface and considerable changes in the potential are accounted for by the formation of basic nickel compounds and their adsorption on rhe electrode surface.