Effects of thiourea and urea on zinc–cobalt electrodeposition under continuous current

Abstract

The effect of thiourea and urea on zinc-cobalt alloys obtained from chloride baths under continuous current deposition are described and discussed. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The use of additives does not refine the grain size of the Zn-Co alloy and an especially porous alloy was produced in the presence of urea. The preferred crystallographic orientations of zinc-cobalt alloys do not change in the presence additives. Zinc-cobalt alloys were without texture in the presence and absence of additives. Also, in the absence of additive and in the presence of urea, the XRD lines of the Zn-Co alloys are slightly shifted with respect to the pure zinc XRD lines, whereas, in the presence of thiourea, the XRD lines are not shifted. The alloy composition was examined using Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases slightly from 1.04 to 0.91 wt.% in the presence of urea and in the presence of thiourea it increases from 1.04 to 7.70 wt.%. Voltammetric studies show that thiourea increases the reduction rate of cobalt. This explains the increase in cobalt percentage in the alloy in the presence of thiourea.

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