2014 Volume 54 Issue 7 Pages 1653-1660
Zn electrodeposition was performed galvanostatically on steel sheets at 1500 A/m2 in an agitated sulfate solution at 40°C to investigate the effect of preadsorption of organic additives on the lightness and morphology of Zn. The organic additives employed were classified into two types: 1) polyethylene glycol (PEG), gelatin, and stearyl dimethylbenzyl ammonium chloride (SDBAC) (Type I), which exhibit a polarization effect for Zn deposition; and 2) saccharin and sodium lauryl sulfate (Type II), which exhibit no polarization effect for Zn deposition. The platelet crystals of deposited Zn were reduced in size with preadsorption of all the organic additives considered. The observed decrease in the size of Zn platelet crystals with preadsorption is attributed to both an increase in the overpotential for Zn deposition and a decrease in the epitaxial growth of Zn on steel substrates. The preferred orientation of the {0001} Zn basal plane significantly decreased because of an increase in Zn deposition overpotential owing to preadsorption of PEG and gelatin, and the orientation slightly decreased with saccharin and sodium lauryl sulfate in spite of the absence of a polarization effect on Zn deposition. The surface roughness of deposited Zn decreased with preadsorption of organic additives with the exception of SDBAC. This is due to a decrease in the size of Zn platelet crystals. The lightness of deposited Zn was increased by preadsorption of organic additives with the exception of SDBAC. Because Zn deposited nonuniformly with preadsorption of SDBAC, the surface roughness of Zn increased and the lightness decreased.
