Gold and Gold Alloys Electropolishing in Choline Chloride-Glycerol Deep Eutectic Solvents
Authors: Rodriguez Julymar , Ziza Ahamadi Nesly , Doche Marie-Laure , Hihn Jean-Yves 
Published: December 2024

Electropolishing is a finishing technique used to reduce the roughness of metallic surfaces while enhancing their brightness. Based on anodic dissolution, this process enables the treatment of parts with complex geometries and reduces processing time compared to conventional mechanical finishing methods.

Concerning precious metals, the use of electrolytes containing cyanides and other toxic compounds reduces EP’s attractiveness from an industrial standpoint. A further challenge lies in the difficulty of dissolving alloy elements in a homogeneous way1. It often requires the adjustment of operating parameters or even of the electrolyte composition for each alloy. In addition, the underlying mechanisms that govern the process are not fully understood, making it more difficult to scale up. As a result, it has become essential to explore high-performance electrolyte solutions while complying with environmental and health safety standards.

Deep Eutectic Solvents (DES) are emerging as a good alternative for the chemical2 and electrochemical3 dissolution of metals. Their advantages include an extended electrochemical window compared with aqueous electrolytes, non-toxicity, and moderate cost3,4. They have already demonstrated their effectiveness on a wide selection of metals, including silver5 and copper3, elements often present in gold alloys.

This work aims to evaluate the effectiveness of choline chloride-based DESs in the electropolishing process of 18K gold alloys. Their performance will be assessed in terms of roughness reduction, brightness enhancement and color preservation, all characteristics associated with the presence of uniform dissolution. The electrochemical mechanisms involved will also be examined.

(1) Rodriguez J. ; Doche M-L ; Hihn J-Y ; Electropolishing of gold and gold alloys in HCl-glycerol-ethanol electrolytes App. Surf. Sci. Adv. 21(2024) 100604 https://doi.org/10.1016/j.apsadv.2024.100604

(2) Jenkin, G. R. T.; Al-Bassam, A. Z. M.; Harris, R. C.; Abbott, A. P.; Smith, D. J.; Holwell, D. A.; Chapman, R. J.; Stanley, C. J. The Application of Deep Eutectic Solvent Ionic Liquids for Environmentally-Friendly Dissolution and Recovery of Precious Metals. Miner. Eng. 2016, 87, 18–24. https://doi.org/10.1016/j.mineng.2015.09.026.

(3) Lebedeva, O. Metals | Free Full-Text | Advantages of Electrochemical Polishing of Metals and Alloys in Ionic Liquids. Metals 2021. https://doi.org/10.3390/met11060959.

(4) Sánchez-Ortiz, W.; Aldana-González, J.; Manh, T. L.; Romero-Romo, M.; Mejía-Caballero, I.; Ramírez-Silva, M. T.; Arce-Estrada, E. M.; Mugica-Álvarez, V.; Palomar-Pardavé, M. A Deep Eutectic Solvent as Leaching Agent and Electrolytic Bath for Silver Recovery from Spent Silver Oxide Batteries. J. Electrochem. Soc. 2021, 168 (1), 016508. https://doi.org/10.1149/1945-7111/abdb01.

(5) Loftis, J. D.; Abdel-Fattah, T. M. Nanoscale Electropolishing of High-Purity Silver with a Deep Eutectic Solvent. Colloids Surf. Physicochem. Eng. Asp. 2016, 511, 113–119. https://doi.org/10.1016/j.colsurfa.2016.09.013.

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