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Nickel Deposition from a Watts Bath Containing Monosodium Glutamate
by Magdy A.M. Ibrahim, F.T. Al Wadaani1and O. Al Jaldi
Chemistry Department, Faculty of Science, Taibah University, Al Maddinah Al Mounwara, KSA
Nickel electrodeposition onto copper substrates was carried out from a Watts bath in the presence of monosodium glutamate (MSG) as a complexing agent. The study dealt with the influence of MSG concentrations on the cathodic current efficiency, cathodic polarization curves, anodic linear stripping voltammetry and the throwing power as well as the throwing index of the bath. The presence of MSG resulted in a marked shift in the polarization curves towards more negative potential values, indicating an inhibition of Ni+2 ion deposition. On the other hand, the extent of the inhibition increased with increasing MSG concentration. The addition of MSG improved the appearance of nickel deposited from the Watts bath. Moreover, the throwing power increased by a factor of more than three in the presence of MSG. The surface morphology of the nickel plated with and without MSG was examined using scanning electron microscopy (SEM), while the microstructure was examined using x-ray diffraction (XRD).
Keywords: nickel electrodeposition, Watts bath, monosodium glutamate, potentiodynamic polarization, throwing power.
Nickel electrodeposition is one of the most widely used surface finishing processes for decorative, engineering and electroforming applications.1 Decorative applications account for about 80% of nickel consumption in plating while 20% is consumed for engineering and electroforming aims.2 In electrodeposition processes, it is not enough just to produce deposits having the desired appearance and properties. The deposit must also be applied in such a way as to completely cover the substrate with a deposit as near uniform in thickness as practicable.3
It is well known that the structural and the mechanical properties are strongly influenced by the electrolyte parameters: composition, temperature, pH and agitation of the electrolytic bath, presence and concentration of additives in the bath, mode of imposed current and current density values. Among these factors, one of the most effective in controlling the nickel crystal growth and the resultant properties of the deposits is the use of complexing agents in the bath. Nickel electrodeposition has been studied extensively by several investigators and deposition has been carried out from different baths including, sulfamate, chloride, sulfate, citrate or acetate baths, in addition to the well-known mixed chloride-sulfate Watts bath, with or without additives.4-16 The current work aims to develop new baths for producing good quality nickel deposits, which have the advantages of being more environmentally friendly.
The electrodeposition of nickel was carried out using a bath containing: 0.63M NiSO4∙6H2O, 0.09M NiCl2∙6H2O and 0.3M H3BO3, commonly known as the Watts bath. All of the plating baths and reagents were made from analytical grade chemicals without further purification and doubly distilled water. Monosodium glutamate (MSG) was added to the Watts bath as a complexing agent. MSG is the sodium salt of glutamic acid (C5H8NNaO4), one of the most abundant naturally occurring non-essential amino acids.17 It has the following chemical structure: