Aging of the HF−H2SO4 electrolyte used for the electropolishing of niobium superconducting radio frequency cavities: Origins and cure

Electropolishing (EP) in the HF−H2SO4 electrolyte is the most desirable surface treatment for niobium superconducting radio frequency cavities yet demonstrated, in terms of performance and surface finish. However, the efficiency of the electrolyte declines quickly with time (decrease in removal rate...

Full description

Saved in:
Bibliographic Details
Published in:Physical review. Accelerators and beams 2010-08, Vol.13 (8)
Main Authors: Eozénou, F, Berry, S, Antoine, C, Gasser, Y, J.-P. Charrier
Format: Article
Language:English
Subjects:
Diffusion coefficient
Electrochemical impedance spectroscopy
Electrolytes
Fluorine
Holes
Mass transport
Moisture content
Niobium
Rotating disks
Sulfur
Sulfuric acid
Superconductivity
Surface finish
Surface treatment
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Electropolishing (EP) in the HF−H2SO4 electrolyte is the most desirable surface treatment for niobium superconducting radio frequency cavities yet demonstrated, in terms of performance and surface finish. However, the efficiency of the electrolyte declines quickly with time (decrease in removal rate, deterioration of the niobium surface, increased sulfur generation). Previous studies at CEA Saclay have highlighted the impact of the water content in EP mixtures rather than the content of dissolved niobium. Knowledge of the electrochemical system was improved thanks to studies using a rotating disk electrode (RDE). Measurements with a RDE give precious information concerning mass transport of the different ionic groups present in the solution. The performed measurements prove that EP is controlled by the diffusion of fluorine ions and the value of the related diffusion coefficient DF− was estimated for different mixtures. Electrochemical impedance spectroscopy (EIS) measurements were also performed with different EP mixtures. Both volt ampere metric and EIS measurements prove the central role of fluorine during EP and show that EP mechanisms evolve with the aging of the bath. Another major problem related to electrolytes is the formation of impurities such as sulfur. We have proved that working at a reduced voltage of 5 V does not alter cavity performance and makes it possible to reduce the undesirable particulate contamination in electrolytes and to increase their lifetime.
ISSN:2469-9888
DOI:10.1103/PhysRevSTAB.13.083501