Apparatus for the electrolytic polishing of niobium structures

Abstract

A hollow niobium body, rotatable about a horizontal axis, is arranged for partial immersion in an electrolyte of H.sub.2 SO.sub.4, HF and H.sub.2 O. A generally concentric opening at one end receives a cathode. Evolved gases rise therefrom and escape into a vapor space above without contacting the immersed surfaces of the niobium body. The cathode is hollow and is perforate in the portion introduced into the body in order to feed electrolyte into the body. For polishing, constant electric voltage is applied between the hollow niobium body and the cathode and adjusted in such a manner that damped current oscillations occur which are superimposed on the electrolytic current. Not later than after the complete decay of the current oscillations, the voltage is turned off until the oxide layer built up during the current oscillations is dissolved. Subsequently, a constant voltage is again adjusted in such a manner that damped current oscillations occur, and the sequence of states with the voltage turned on and off is repeated several more times. During the application of the constant voltage and the subsequent dissolution of the oxide layer, the hollow niobium body is kept at rest and its rotation about the axis of rotation is continued after the oxide layer is dissolved and before the constant voltage is applied again.

Dependencies are inferred from the claim text.