Prediction of morphology development from nucleation and plating overpotentials in nickel electrodeposition

ABSTRACT

Evaluation and measurement of the influence of changes in conditions and electrolyte composition during early stages of a growing metal electrodeposit are crucial to predict changes in developing morphology. A galvanodynamic polarisation technique was developed to reliably measure overpotentials for nickel electrodeposition from sulphate electrolyte. The validity of these polarisation parameters as indicators of the relationships between changes in the electrolyte and resulting deposit morphology was evaluated for electrolytes of varying composition. Findings indicate that nucleation and plating overpotentials measured by the described technique can be used as indicative tools for monitoring, evaluating and ultimately improving control of the electrodeposition of nickel from sulphate electrolytes. The results predict that nickel deposits of desirable quality and morphology are obtained when plating overpotentials are higher than 700 mV vs. Ag/AgCl and nucleation overpotential is less negative than plating overpotential.

RÉSUMÉ

L’évaluation et la mesure de l’influence des changements de conditions et de la composition de l’électrolyte lors des premières étapes de dépôt électrolytique d’un métal en croissance sont d’importance cruciale pour prédire les changements de la morphologie en développement. On a développé une technique de polarisation galvano dynamique afin de mesurer de façon fiable les surtensions pour l’électrodéposition du nickel à partir d’électrolyte de sulfate. On a évalué la validité de ces paramètres de polarisation comme indicateurs des relations entre les changements de l’électrolyte et la morphologie résultante du dépôt, pour des électrolytes de composition variable. Les résultats indiquent que l’on peut utiliser les surtensions mesurées de nucléation et de placage par la technique décrite, comme outils indicateurs pour le monitorage, l’évaluation et ultimement pour l’amélioration du contrôle de l’électrodéposition du nickel à partir d’électrolytes de sulfate. Les résultats prédisent que des dépôts de nickel de qualité et de morphologie désirables sont obtenus lorsque les surtensions de placage sont plus élevées que 700 mV par rapport à Ag/AgCl et que la surtension de nucléation est moins négative que la surtension de placage.

KEYWORDS:

• Electrocrystallisation
• electrowinning
• morphology
• nickel
• nucleation
• polarisation
• sulphate

Acknowledgements

Our appreciation is extended to the two referees who provided extremely valuable and useful comments on earlier versions of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Liezl Schoeman is a research scientist at the Industrial Metals and Minerals Research Institute (IMMRI) based at the University of Pretoria, South Africa. She obtained her Bachelor, Honours and Master’s degrees from the University of Johannesburg and is currently pursuing a doctorate at the University of Pretoria. Her work and research interests include hydrometallurgy, specifically electrowinning and corrosion, surface chemistry of metals and the chemistry of organic coatings. Liezl works closely with industry and is currently involved in various projects with Arcelor Mittal (AMSA).

Kathryn C. Sole (PrEng, PhD, FSAIMM) obtained her PhD from the University of Arizona, U.S.A., following BSc(Hons) and MSc degrees from Rhodes University, South Africa. She has authored over 90 publications, mainly in the areas of solvent extraction, ion exchange, and electrowinning of base and precious metals for hydrometallurgical applications. She has been awarded the Silver Medal of the Southern African Institute of Mining and Metallurgy and Bronze Medal of the South African Association for the Advancement of Science. She is an independent hydrometallurgy consultant and holds an honorary position at the University of Pretoria.

ORCID

L. Schoeman http://orcid.org/0000-0002-2925-1829

K. C. Sole http://orcid.org/0000-0003-4707-1060

Additional information

Funding

The Industrial Metals and Minerals Research Institute (IMMRI) based at the University of Pretoria provided some support for project costs.