Undergraduate Research at Jefferson Lab

Characterization of a Novel HF-free Electrolyte for Niobium Polishing

Student: Angelica N. Jusino

School: Christopher Newport University

Mentored By: Charlie Reece and Hui Tian

Niobium particle accelerator cavities require smooth internal surfaces to perform well, and electrochemical polishing (EP) is a method used. The common electrolyte is a concentrated mixture of hydrofluoric and sulfuric acid, which is effective, but also very dangerous and costly. Recently, an acid-free vitamin B₄ electrolyte has been introduced and has shown promising results. In this study, the acid-free electrolyte was studied further to understand its characteristics and the mechanisms of the EP process. First, the solution was characterized with viscometry and a rotating disk electrode was used to determine the factors contributing to the current limited plateau. Electrochemical impedance spectroscopy was used to study the cell's temperature and voltage dependence. With the collected data, we were able to better understand the novel electrolyte as well as begin to understand the EP reaction. The results presented here begin to explain the mechanisms and verify the effectiveness of the new system. It was determined that mechanism that produces the current-limited plateau is independent of the diffusion, in strong contrast to the HF-based EP process, and that the reaction is significantly temperature and voltage dependent. Some of the data presented requires future work to support and explain its findings. Overall, the vitamin B₄ electrolyte has promising results with understood mechanisms, and can eventually render the costly and dangerous acid-based system obsolete.