Stainless steel substrate pretreatment effects on copper nucleation and stripping during copper electrowinning
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RESEARCH ARTICLE
Stainless steel substrate pretreatment effects on copper nucleation and stripping during copper electrowinning Florian Verbruggen1,2 · Erika Fiset1,2,5 · Luiza Bonin1,2 · Antonin Prévoteau1,2 · Michael S. Moats4 · Tom Hennebel1,2,3 · Korneel Rabaey1,2 Received: 29 June 2020 / Revised: 11 September 2020 / Accepted: 14 September 2020 © Springer Nature B.V. 2020
Abstract The effects of surface pretreatment of 304 stainless steel (SS) substrates on copper film formation, adhesion, and purity obtained by galvanostatic electrodeposition at a current density of – 30 mA cm−2 are presented. The polished substrate produced more copper nuclei, resulting in an increase of the adhesion as compared to chemically oxidized SS substrate. The adhesion of the copper deposits was characterized by a Nano-scratch tester (NST). The nucleation behavior is associated with the flatband potential of the SS surface, which was derived from capacitance measurements. The grain size of copper deposits was characterized by field emission scanning electron microscopy (FESEM). Copper grains were smaller on the polished SS with a size of less than 1 µm after 5 min of electrodeposition. High-purity copper deposits with 130 (N = 0) 94 ± 10 (N = 7)
N the number out of nine observations in which the damage feature took place within the assesed load range (max = 130 mN)
high nucleation rates and fast copper coverage on the polished substrate resulted in the smoothest copper deposits compared to the oxidized substrate. The adhesion properties of the copper deposits on the oxidized and polished substrates were assessed through careful observation of the damage features and their position along the track (critical load (mN)). The goal of the scratch test was not to obtain the exact adhesion strength of the copper deposits to the SS substrate. The term adhesion is used in a relative context. The critical load values of adhesion failures were used to indicate the general ability to resist the physical handling associated with commercial operations such as automatic stripping in copper electrowinning. The damage features and values of the critical load are given in Table 1, and the microscopy images of the indented scratches and damage features are provided in Figure S6. The scratches in the copper deposits on the polished substrate were smooth and shallow (Figure S6b). This suggests that the copper deposit showed high elastic recovering properties at loads below 130 mN. A transverse tensile crack was observed towards the end of the scratch (97 ± 11 mN), which represents a cohesive failure in the copper deposit. No adhesion failures were observed in the operated load range. The scratches in the copper deposits on the oxidized were rough and shallow, which implies reduced cohesiveness and high elastic recovery properties at loads below 130 mN. A transverse tensile crack occurred at a lower load (53 ± 24 mN) comparing with the copper deposits on the polished substrate. In contrast to the copper deposits on the polished substra
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