SRF2011 - List of Authors (Sumption, M.)

Paper	Title	Page
TUPO068	Electropolishing of Niobium to Obtain Defect Free Surface	561
	A. Chandra, G. Frankel, M. Sumption Ohio State University, USA
	Funding: This work supported by United States Department of Energy Grant DE-SC0004217 The SRF cavities needs to have a good surface finish to achieve maximum performance. Surface defects like grain boundaries, bumps and pits limit the maximum field gradients achieved. Electropolishing (EP) is commonly used as a final surface finishing process. Acid concentration, stirring, temperature and amount of material removed are the parameters expected to affect the surface finish and their effect is studied using flat Nb specimens. Optical microscope, SEM and optical profilometer have been used to characterize the level of surface finish obtained. The mechanism of EP is not fully understood. To explore the mechanism and parameters necessary for optimum surface finish, an electrolytic cell made of 99.999% pure Al has been designed which also serves as the counter electrode. The mechanism involves the formation of a viscous layer on the Nb surface. There is evidence for the formation of this film in electrochemical experiment results and optical observations. The film is in fact critical to the EP mechanism as it has been found that the surface is pitted where a stable viscous film can not be formed.

Paper

Title

Page

Electropolishing of Niobium to Obtain Defect Free Surface

561

A. Chandra, G. Frankel, M. Sumption
Ohio State University, USA

Funding: This work supported by United States Department of Energy Grant DE-SC0004217
The SRF cavities needs to have a good surface finish to achieve maximum performance. Surface defects like grain boundaries, bumps and pits limit the maximum field gradients achieved. Electropolishing (EP) is commonly used as a final surface finishing process. Acid concentration, stirring, temperature and amount of material removed are the parameters expected to affect the surface finish and their effect is studied using flat Nb specimens. Optical microscope, SEM and optical profilometer have been used to characterize the level of surface finish obtained. The mechanism of EP is not fully understood. To explore the mechanism and parameters necessary for optimum surface finish, an electrolytic cell made of 99.999% pure Al has been designed which also serves as the counter electrode. The mechanism involves the formation of a viscous layer on the Nb surface. There is evidence for the formation of this film in electrochemical experiment results and optical observations. The film is in fact critical to the EP mechanism as it has been found that the surface is pitted where a stable viscous film can not be formed.