Chemical polishing of niobium workpieces, esp. cavity resonator - by brief immersion in mixt. of conc. hydrofluoric, nitric and sulphuric acids

摘要

The workpieces are polished in a bath which is heated to min. 40 deg.C, and is pref. at min. 70 deg.C. The bath has a vol. which is at least 15, and pref. min. 50 times the vol. of the workpiece; and contains by wt. 5-10% HF, 11-26% HNO3, 36-66% H2SO4, the remainder being water. The pref. bath contains 6.5-8.5% HF, 12.5-19.5% HNO3, 46-62% H2SO4, rest H2O. The esp. pref. bath (A) contains 7.3% HF, 14'7% HNO3, 56.9% H2SO4, 21.1% water. The Nb workpieces are pref. immersed in a freshly mixed acid bath in which the H2SO4 is the last acid to be added to the mixt. Process is used e.g. for superconducting cavity resonators. A highly polished surface can be obtd. without the Nb being etched.