Chemical Polishing of Niobium for Superconducting Radio Frequency Cavity

The polishing rate, surface topography, chemical composition and grain orientation of the chemical polishing process for niobium metal were analyzed to optimize process parameters. The mixed solution (hydrofluoric acid: nitric acid: phosphoric acid=1:1:2, volume ratio) was proposed as appropriate polishing reagents with rate equation h=29.359t(0.9247). Polishing for 6 similar to 15 min can remove 154 similar to 360 mu m of material using this solution, and roughness R-a and Nb2O5 layer thickness of polished surface is less than 0.65 mu m and 10 nm, respectively. Meanwhile, the polishing mechanism was discussed using electron back scatter diffraction (EBSD) and laser scanning confocal microscope (LSCM). We find that the outmost surface of over-polishing sample consists of many fine high-index planes which intersect each other to form sharp edges in grains or at boundaries.