Three-Dimensional Simulation of Solution-Contact Electrolytic Dissolution
Authors: Pereira Drew Joseph , Boyer Hailey R. , Truong Thanh-Tam , Martinez-Rodriguez Michael Joe , Shimpalee Sirivatch 
Published: December 2020

Electrochemical dissolution is a process where a metal is dissolved via oxidation and can be controlled through electrolyte properties, electrolyte flow, and applied potential. Electrochemical dissolution is employed in many manufacturing applications such as electrochemical machining, electrochemical pickling, metal refining, metal surface finishing, etc. Most of these dissolution applications use a traditional metal-contact method (metal being dissolved is in direct contact with the anode); however, some applications will have phenomena that cause operational issues, safety issues, or damage to the dissolver components. These phenomena include (1) difficulty maintaining contact, (2) arcing/sparking[1] in a flammable environment, which occurs because of a build-up of oxide, or (3) overheating, which can cause melting during dissolution. To avoid unsafe or destructive phenomena, a solution-contact electrolytic dissolution (SCED) method (metal being dissolved is only in contact with electrolyte) can be employed. Here, a three-dimensional model is developed to simulate solution-contact electrolytic dissolution in a small-scale system for the first time.

A representation of a small-scale SCED system is shown in Figure 1. This system takes place within a HNO3 solution and includes a Pt anode and cathode where water-splitting and hydrogen formation occur, respectively. The sample coupon (our target for dissolution) acts as a physical barrier, so hydrogen ions gather on the anode-side of the sample coupon, forming a positively charged region, while H+ ions are consumed on the cathode-side of the coupon, leaving a negatively charged region. This imbalance of charge, along with the potential profile that forms within the system when voltage is applied to the anode, drive reactions to occur on the surface of the sample coupon. The reactions include the ejection of a metal ion, Mν+, towards the negatively charged region, while H+ ions combine with the free e-s released from the metal dissolution reaction to form hydrogen gas. The model theory developed here is able to predict stray currents in the solution-phase, a useful design tool to avoid corrosion of other components within an electrochemical system. [2-3] Discussion over important phenomena that must be properly represented to simulate this electrolytic dissolution process will take place, including electrochemical species transport, local surface reaction rates (using Butler-Volmer kinetics), and electrodynamic potential.

References

[1] McGeough, J. A., Khayry, A. B. M., Munro, W., & Crookall, J. R. (1983). Theoretical and experimental investigation of the relative effects of spark erosion and electrochemical dissolution in electrochemical arc machining. CIRP Annals, 32(1), 113-118.

[2] Wang, D., He, B., & Cao, W. (2019). Enhancement of the Localization Effect during Electrochemical Machining of Inconel 718 by Using an Alkaline Solution. Applied Sciences, 9(4), 690.

[3] Wang, D., Zhu, Z., Bao, J., & Zhu, D. (2015). Reduction of stray corrosion by using iron coating in NaNO 3 solution during electrochemical machining. The International Journal of Advanced Manufacturing Technology, 76(5-8), 1365-1370.

Figure 1. Representation of the local electrochemical reactions that take place in a small-scale SCED system.

Figure 1