Influence of disodium ethylenediaminetetraacetate on zinc electrodeposition process and on the morphology, chemical composition and structure of the electrodeposits

Abstract

Zinc electrodeposition on 1010 steel substrate, from an alkaline solution containing various EDTA concentrations, was investigated by cyclic voltammetry. The analysis of the voltammetric curves, showed, irrespective of EDTA concentration, the presence of a well defined pre-bulk region (region peak c0), where the Zn underpotential deposition (UPD), hydrogen evolution reaction (HER) and reduction of iron oxide compete, which was followed by region of peak c1, where Zn bulk electrodeposition (overpotential deposition (OPD)) occurred. AFM and XRF analysis of Zn electrodeposit on 1010 steel substrate produced voltammetrically in the region of peak c0 showed presence of Zn. These results corroborate those obtained by cyclic voltammetry, i.e., that Zn UPD occurred in the region of peak c0. The morphological, structural and the chemical composition characterization of the Zn electrodeposits prepared potentiostatically at −1.60V, were performed by SEM, XRD and EDS, respectively. SEM images showed that the size of Zn crystallites produced at deposition charge densities (qd) of 2.0Ccm−2 and 10.0Ccm−2 decreased in the presence of EDTA, except at 0.20M EDTA and qd 10.0Ccm−2. EDS analysis showed that incorporation of oxygen in the electrodeposits depended on both qd and EDTA concentration. XRD patterns of the electrodeposits produced indicated only phase of pure Zn, with various reflections, irrespective the presence of EDTA and qd. These electrodeposits exhibited crystallites preferentially oriented parallel to the (002) plane. Although EDTA led to morphological and chemical composition changes, it did not produce significant micro-structural changes, which could lead to different crystallographic orientations.