Effect of polyethylene glycol and glue on electrodeposition behavior of Zn from electrowinning solution and its crystal structure

To elucidate the effects of polyethylene glycol (PEG) and glue on the deposition behavior of Zn from electrowinning solutions and its crystal structure, Zn electrodeposition was performed at a current density of 600 A-m-² and a charge of 8.64 × 10 Cm-² in an agitated sulfate solution containing 1.07 moldm-³ and 1.8 moldm-³ of ZnSO and H SO, respectively, at a temperature of 45°C. With the additions of PEG and glue, the evolution of hydrogen was suppressed at current density region less than the critical current density for Zn deposition, resulting in decrease in critical current density of Zn. The degree of decrease in critical current density of Zn was larger with glue than that with PEG. The current efficiency for Zn deposition was higher with PEG and glue than that without at low current density region because the critical current density of Zn decreased with additives. Since the additives suppressed Zn deposition more than the hydrogen evolution at high current density region, the current efficiency of Zn decreased with increasing concentration of additives in solution. At high current density region, there was little difference in current efficiency of Zn between PEG and glue. The effect of molecular weight of PEG on the current efficiency of Zn was rarely observed at molecular weight above 2000. With an addition of PEG, the deposits became fine platelets crystals with preferred orientation of {1011} and layered pyramidally, while the deposits orientated to {1120} preferentially and the platelets crystals grew perpendicularly to the substrate with an addition of glue. The surface roughness of deposited Zn decreased with additives and it was smaller with PEG than that with glue.