We have performed screening tests on candidate solutions to replace hazardous acidic mixtures, such as HF, HNO_3 and H_3PO_4, for the electrochemical polishing of niobium (Nb) superconducting radio frequency (SRF) cavities. The best results, in terms of surface roughness, were found for a relatively environmentally-benign mixture of ionic liquids: vitamin B_4 (2-hydroxyethyl-trimethylammonium) chloride, urea, ethylene glycol and ammonium fluoride. Scanning electron microscope (SEM) imaging and atomic force microscopy (AFM) were used to compare the quality of a electrochemical polished surface by ionic liquids (IC) sample and a as-received (AR) sample. The average roughness, Ra, found for one of the (50×50 μm) IC areas examined, was 22 nm. These results suggest the possibility of an effective green process to be used during the production of Nb superconducting radio frequency cavities for the International Linear Collider (ILC).
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