Stainless steel substrate pretreatment effects on copper nucleation and stripping during copper electrowinning

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 mu m after 5 min of electrodeposition. High-purity copper deposits with < 1 ppm S (detection limit) were obtained on the oxidized SS substrate compared to 2.5 ppm for the polished SS substrate. Atomic force microscopy (AFM) measurements showed that the copper deposits were 25% less rough on the polished SS as compared to the oxidized SS. The results indicate that the obtained purity of the copper deposit relates to the grain size of the deposit, rather than the initial surface roughness. In the context of industrial electrowinning, high adherence to the polished substrate could increase the operation time of the copper cathode stripping. Hence for electrowinning from copper sulfate electrolytes, oxidizing the SS surface prior to deposition could lead to higher purity along with enhanced stripping.

Publication year:2021

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