Evaluation of the diffusion coefficient of the fluorine during the electropolishing of niobium

Conference · Sun Nov 01 04:00:00 EST 2009

DOI:https://doi.org/10.1103/PhysRevSTAB.13.083502· OSTI ID:1999155

Tian, Hui; Reece, Charles

Future accelerators, such as the envisioned international linear collider (ILC), require unprecedented cavity performance, which is strongly influenced by interior surface nano-smoothness. Electropolishing (EP) is the current technique of choice being developed for high?field superconducting radio frequency (SRF) cavities. Previous study shows that the EP mechanism of Nb in 1:9 volume ratio of H2SO4/HF acid electrolyte proceeds by formation and dissolution of a compact salt film under F- diffusion-limited mass transport control [1]. We pursue an improved understanding of the microscopic conditions required for optimum surface leveling. The temperature-dependent viscosity of the standard electrolyte has been measured and, using a rotating Nb disk electrode, the diffusion coefficient of F- was measured at a variety of temperatures from 0oC to 50oC. In addition, data indicates that above 25oC electrode kinetics becoming competitive with the mass transfer current limitation and increases dramatically with temperature. These findings are expected to guide the optimization of EP process parameters for achieving controlled, reproducible and uniform nano-smooth surface finishing for SRF cavities. References: [1] H. Tian, S. G. Corcoran, C. E. Reece, M. J. Kelley, Journal of the Electrochemical Society, v 155, n 9, Sept. 2008, p 563-8 This work was authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1999155
• Report Number(s): JLAB-ACC-09-1085; DOE/OR/23177-1016
• Country of Publication: United States
• Language: English