Structural Properties of Electrolytic Nickel Deposits Produced By Direct, Pulse and Pulse Reverse Currents in the Organic-Free Watts Electrolytes

Nickel plating is one of the most frequently used surface treatments because of good chemical, mechanical, magnetic, optical and electrical properties of coatings. The major application areas include corrosion protective coatings, bright underneath coatings, diffusion barrier coatings and electroforming. Each one of these applications require different characteristics for the electrodeposits. Therefore, numerous studies were performed to see the effects of plating parameters on the final characteristics of nickel electrodeposits such as grain size, roughness, ductility and internal stress [1-3].    

In this study, characteristics of Ni deposits obtained from synergetic investigation of pulse and pulse reverse current plating parameters in the selected Watts electrolyte were compared. Even though various researches were conducted to understand the effects of each pulse plating parameter, interactions between the parameters were not considered in most of these studies. In other words, the experiments were performed by changing one parameter at a time and keeping the others constant. It is not possible to determine the combined effects of the parameters with such an approach. Moreover, most of the articles focused on only one of the structural properties (grain size, corrosion resistance, etc) and the experiments were conducted out of the limits of capacitive effect and mass transport conditions.

The plating conditions within the limits of capacitive effect and mass transport were determined by full factorial design for pulse and pulse reverse applications. Comparison and characterization of nickel electrodeposits were performed by potentiometry, SEM, XRD, XRF and roughness analyses. The nickel electrodeposits of different structural properties were obtained by direct, pulse, and pulse reverse currents in the organic free Watts solution. Smoothest nickel deposits of (200) preferred orientation were obtained by pulse reverse technique, where positive and negative applied currents were 100 and 55 mA/cm², respectively. 67 nm average roughness at the nickel surface was achieved without coloring of edges at approximately 50 percent cathodic current efficiency.

References

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[2] F. Denise and H. Leidheiser, "An X‐ray study of the effect of organic compounds on the crystal growth of nickel during electrodeposition," Journal of Electrochemical Society, vol. 100, no. 11, p. 490, 1953.

[3] J.-m. Zhang, K.-w. Xu and V. Ji, "Dependence of stresses on grain orientation in thin polycrytalline films on substrates: an explanation of the relationship between preferred orientations and stresses," Applied Surface Science, vol. 180, pp. 1-5, 2001.