Effect of additives on electrodeposition of nanocrystalline zinc from acidic sulfate solutions

The influence of polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB), benzalacetone (BA), and thiourea (TU) on pulse electrodeposition of zinc from acidic sulfate baths was investigated by X-ray diffraction, scanning electron microscopy, and potentiodynamic polarization techniques. The results show that a mixture of PEG and CTAB can fully dissolve BA in the concentrated zinc sulfate solutions. This ternary additive can increase the overpotential of zinc electrodeposition markedly, and then gives rise to forming a bright nanocrystalline zinc coating on steel substrate, with an average grain size of 52 nm. The combination of these four compounds is more powerful for improving the cathodic polarization and inhibit hydrogen evolution during zinc electrodeposition in comparison with ternary additive systems. A bright and compact zinc coating with a grain size of 43 nm and the (110)(100)(201) preferred orientations are produced due to the coexistence of all four compounds. These compounds act in a synergetic way, especially between BA and TU, leading to the grain refinement of zinc deposits.