Dendritic Zinc Growth in Acid Electrolyte: Effect of the pH
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JMEPEG (2018) 27:1103–1108 https://doi.org/10.1007/s11665-018-3139-7
Dendritic Zinc Growth in Acid Electrolyte: Effect of the pH Leandro N. Bengoa, Paola Pary, Pablo R. Sere´, M. Susana Conconi, and Walter A. Egli (Submitted April 11, 2017; in revised form December 4, 2017; published online January 30, 2018) In this paper, dendritic growth at the edges of electrogalvanized steel strip has been studied using a specially designed rotating washer electrode which simulates the fluid dynamic conditions and the current density distribution at the steel strip edge found in a production line. The effect of electrolyte pH and current density on dendritic growth in an acidic zinc plating bath (ZnSO4 and H2SO4) was addressed. The temperature was kept constant at 60 °C. Solution pH was adjusted to 1, 2 or 3 using different amounts of H2SO4. In addition, the influence of temperature on the pH of the solution was determined. The current density was set at 40 or 60 A/dm2, similar to that used in the industry. Deposits were characterized using SEM and XRD. The results showed that pH strongly affects dendrites shape, length and texture. Furthermore, the morphology of dendrites at the washer edge and of deposits on the flat portion of the washer changed considerably as solution pH was increased from 1 to 3. It was found that the morphology of dendrites at the washer edge stems from the morphology of the deposit on its flat portion, which in turn determines their shape. Keywords
crystal growth, dendrites, electrodeposits, texture, zinc
1. Introduction Dendritic growth during metal electrodeposition has been studied by many authors since the middle of the twentieth century (Ref 1-7). In general, these studies were focused on theoretical aspects of the phenomenon, which has allowed the development of theories and models that properly fit the experimental evidence. In spite of the relevance of these results, they have been obtained under static conditions and using very simple geometries while the study of industrial situations, where the formation of dendrites gives rise to quality problems, has not been addressed yet. For example, the occurrence of this type of zinc crystal growth during the continuous electrogalvanizing of steel strip in acid medium usually causes defects that translate into customersÕ claims or rejections of the product. In these processes, the design of the production lines is performed so that the quality of the material obtained in the flat part of the strip is optimized, while the edges are exposed to high current densities (j) caused by current distribution issues (Ref 8). Considering this, a cell especially designed to simulate the fluid dynamic conditions and the current distribution at the edge of the steel strip was built. The cell uses a rotating washer Leandro N. Bengoa and Paola Pary, Centro de Investigacio´n y Desarrollo en Tecnologı´a de Pinturas (CIDEPINT), CICBACONICET, Av. 52 e/121 y 122, 1900 La Plata, Argentina and Engineering School, Universidad Nacional de La Plata, Av.1 y 47, 1900 La Plata, Argentin
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