Synthesis, structure, and properties of nanocrystalline zinc by pulsed-current electrodeposition

Square-wave cathodic current electrodeposition was used to produce for the first time nanocrystalline zinc electrodeposits from both zinc chloride and zinc sulfate-based electrolytes. The influence of pulse electrodeposition parameters and polyacrylamide and thiourea additions on the grain size, surface morphology, and preferred orientation of zinc deposits was determined. The microstructure and surface morphology of the zinc electrodeposits were studied by SEM, FESEM, and AFM. X-ray diffraction was used to determine the preferred orientation of these deposits.; The grain size of zinc deposits decreased gradually with increasing current on-time at constant current off-time and peak current density. An increase in the current off-time at constant current on-time and peak current density resulted in grain growth. A progressive decrease of the grain size was observed with increasing peak current density at constant current on-time and off-time. Nanocrystalline zinc (50 nm) was obtained from the chloride-based electrolyte at on-time of 5 ms, off-time of 9 ms and a peak current density of 1000 mA/cm2. Nanocrystalline zinc with an average grain size of 38 nm was obtained from sulfate-based electrolyte at on-time of 7 ms, off-time of 9 ms and at peak current density of 1200 mA/cm2.; The hardness of nanocrystalline zinc increases from 5 to 8 times higher than that of pure polycrystalline zinc (0.29 GPa). Calorimetric investigations using DSC show two exothermic peaks. The first peak (peak temperature of 429 K) was attributed to the release of internal lattice strain. Abnormal grain growth was observed by the AFM and the second peak from the DSC scan, which begins at 576 K with a peak temperature of 608 K.; Potentiodynamic and alternating current impedance testing of nanocrystalline zinc deposits show that the corrosion current density of nanocrystalline zinc was about 60% lower than that of electrogalvanized (EG) steel, 90 μA/cm 2 and 229 μA/cm2, respectively. The passive film formed on the nanocrystalline zinc surface seems to be a dominating factor for the corrosion behavior observed.