Purification of niobium

The current state of the art in producing pure niobium metal is reviewed, dealing firstly with the fundamental aspects of the gas-metal reactions which are employed in the vacuum purification processes. The application of these techniques in the modern industrial production of niobium by electron-beam melting and solid-state sintering is described with examples based on different starting materials. Also discussed are methods that have been used to produce ultra-pure niobium on a laboratory scale, in particular electrolytic refining and electron-beam float zone melting. An essential aspect of the purification of niobium is the analysis of trace impurities. The techniques currently used are outlined. Finally, the main applications of niobium and its alloys are briefly summarized. (AU)