Pulse current electrodeposition of nanocrystalline zinc

Pulse electrodeposition exhibits marked advantages over direct current electrodeposition in the control of deposit grain size, surface morphology, and preferred orientation. The effect of pulse peak current density (Jp) on the grain size and surface morphology of zinc deposits with additives (polyacrylamide and thiourea) was studied by scanning electron microscopy and field emission scanning electron microscopy. The preferred orientation of zinc deposits was studied by X-ray diffraction, and microhardness of the deposits was measured by a Knoop microhardness tester. Increasing JP dramatically changed the surface morphology and decreased the grain size. Nanocrystalline zinc (56 nm) was produced at JP=2 A cm-2. At JP equal to 0.4 A cm-2, the preferred orientation of zinc deposits was (1 1 2-bar 2) and changed to the prismatic (1 1 2-bar 0) orientation at Jp equal to 0.8, 1.2, and 1.6 A cm-2. However, increasing the peak current density to 2 A cm-2 altered the prismatic (1 1 2-bar 0) to the random (1 0 1-bar 1). The microhardness increased to approximately 8 times higher than that of pure polycrystalline zinc (0.29 GPa). Microhardness reached a maximum (2.3 GPa) at 1.6 A cm-2, then decreased to 1.5 GPa at 2 A cm-2. The hardness drop was correlated with the presence of additives and the change in texture from (1 1 2-bar 0) to the random (1 0 1-bar 1) with increasing Jp