Synergistic effect of L-cysteine and iodide ions during electrodeposition of nanocrystalline nickel from a Watts bath

ABSTRACT

Nickel deposited from the Watts bath with L-cysteine (L-Cys) as a new organic brightener additive, and/or iodide ion was accomplished on a copper cathode. Cathodic polarisation, anodic linear stripping voltammetry, i-t transients, throwing power and cathodic current efficiency were investigated thoroughly. The surface of the produced Ni coatings was analysed using scanning electron microscope and X-ray diffraction (XRD) methods. The results showed that the inhibition of nickel reduction was observed in the presence of L-Cys or in the presence of iodide ions individually. Excellent inhibition was achieved with the addition of a mixture of L-Cys and I⁻ ions due to their co-adsorption on the cathode surface (in a synergistic effect). Moreover, the TP value of the Watts bath in the presence of a mixture of L-Cys and I⁻ ions is four times its value in the absence of this mixture. XRD measurements showed that the (200) level was the most preferred direction for growth and the intensity of all peaks increased considerably with a combination of L-Cys and I⁻ ions. Fine-grained and pit-free deposits that were firmly adherent to the substrate were produced using a combination of L-Cys and NaI.

KEYWORDS:

• L-cysteine
• iodide ions
• polarisation
• chronoamperometry
• throwing power

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