Electrodeposition of white gold alloys: an electrochemical, spectroelectrochemical and structural study of the electrodeposition of Au-Sn alloys in the presence of 4-cyanopyridine

A bath for the electrodeposition of Au-Sn alloys is proposed and the properties of the deposit obtained have been studied, in view of applications in the field of white precious metal plating and electroforming. 4-Cyanopyridine has been employed as an organic additive to confer stability to the bath and compactness to the deposit. The electrochemical behaviour of the bath has been investigated by means of cyclic voltammetry, stripping potentiodynamic scans, open circuit potential decay measurements and potentiostatic transients. The nucleation behaviour of the system has been studied on glassy carbon electrodes. The electrodic behaviour of 4-cyanopyridine was investigated as a function of electrode potential by in situ Raman spectroscopy. The composition of the alloys was evaluated by electron dispersive spectroscopy, the crystalline structure by X-ray diffraction and the morphology by scanning electron microscopy. The effects of the additive on the crystalline structure and on the morphology of the electrodeposits have been highlighted. Potential-dependent adsorption, reorientation and cathodic reactivity of 4-cyanopyridine during the alloy electrodeposition process have been assessed.