Abstract

Niobium has many significant features such as the highest critical transition temperature (9.2 K) of the pure metals and sufficiently high critical magnetic field (>2k Oe), which make it the most widely used materials for construction of superconducting radio frequency (SRF) accelerator cavities. Since the conductivity of niobium metal is a nanoscale, near-surface phenomenon, thus the performance of niobium SRF cavities is strongly impacted by the interior surface chemistry and topography concerning with the surface treatments. Because niobium is easily to form firm passive oxide film preventing further polishing in electrolyte with high water content, the surface damage and contamination of niobium were conventionally removed by method of electropolishing (EP) in sulfuric acid-hydrofluoric acid electrolytes. However, the hydrofluoric acid is hazardous to human health. In order to lower the hazard, we treated niobium surface by EP in sulfuric acid-methanol electrolytes alternatively, and characterized the niobium surfaces by microscopy and profilometry. Results show that the surface roughness is in micron-scale and sensitive to the electrolyte concentration, i.e. the water content, and the surface quality can also be affected by polishing time and environmental temperature.

 

Biography

Xin Zhao received his B.Eng. degree in Mechanical Engineering from University of Science and Technology of China in 2002 and M.S. degree in Applied Physics from The Hong Kong Polytechnic University in 2004. He is currently pursuing his Ph.D. degree under the direction of Prof. S. Corcoran. His work focuses on the electropolishing of niobium.