Effect of current density on morphology of electroplated tin

In this work, tin electroplating from acidic sulphate bath containing stannous sulphate, sulphuric acid and a glycol type additive with a leveller has been studied on steel substrates. The effects of plating current density on microstructural and morphological features are investigated. The structural and morphological characteristics have been studied by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The XRD analysis confirms that the coatings produced by sulphate bath consist of tetragonal (β-Sn) crystal structure. The grain size of the deposits decreases up to a critical current density (∼30 mA cm^-2), and then an increase in grain size is noticed. The coating morphology turns irregular and porous at higher current densities (about 40-50 mA cm^-2) due to the rapid increase in hydrogen evolution as depicted from the secondary electron SEM images. Line profile analysis across the cross-section of the coatings further confirms the absence of any constituent coming from the bath additives.