Effect of surfactant on the morphology and anti-tarnishing behaviour of Ag coatings electrodeposited from a novel cyanide-free thiosulphate-based electroplating bath

Abstract

In the present course of study, mirror-bright silver (Ag) coatings are electrodeposited via pulse galvanostatic route from a cyanide-free thiosulphate-based bath containing cetrimonium bromide (CTAB) as a surfactant. Cyclic voltammetry (CV) and chronoamperometry studies are performed to analyze the mode of nucleation occurring in the presence and absence of CTAB during the deposition of Ag. The electrochemical studies and the corresponding SEM micrographs suggest that in the presence of CTAB, Ag nucleates in the progressive mode. The XRD and EDS analysis confirm the presence of elemental Ag in the deposited coatings. The SEM studies show the morphological variations that occur in the presence and absence of CTAB. The cross-sectional SEM suggests that in the presence of CTAB, a continuous and uniform coating of an average thickness of ∼3.5 µm is deposited. However, in the absence of CTAB, the deposited coating is non-uniform and has a lower thickness. A static immersion test in Na2S environment, followed by EIS measurements, are carried out to study the effect of CTAB on the anti-tarnishing behaviour of Ag coatings. The XPS spectra show that in the absence of CTAB there is a higher concentration of S(2p) and the coatings turn black due to the formation of tarnished layer over them. Therefore, it can be concluded that the coatings deposited in the presence of CTAB have a uniform and compact morphology and are less prone to tarnishing by the sulphide environment. On that account, the bath containing CTAB can be used for producing mirror-bright and tarnish-resistant Ag coatings for long-term aesthetic usage.