抄録
Niobium and niobium alloys have received considerable attention as engineering materials for heat engine applications. In the past several years, the carbothermic reduction-electron beam melting combination method has made it possible to prepare pure niobium metal. In this work, the possibilities and conditions for winning the pure niobium by this process have been examined with regard to the following items: (1) Working conditions and analytical results on the Nb–C–O solid solutions obtained by the carbothermic reduction of Nb2O2 in vacuum. (2) Vacuum degassing in the solid state. (3) Refining of niobium by electron beam melting. (4) Evaporation deoxidation in the form of niobium suboxides.
The mechanism of refining of the niobium metal by the present method can be characterized by the next steps, carbon is removed by degassing as CO and the elimination of oxygen takes place in the form of CO and volatile suboxides such as NbO and NbO2. Both phenomena seem to occur during the refining period in the solid state under the vacuum at 2200 K and the subsequent electron beam melting. Accordingly, the carbon elimination is possible only when an excess of oxygen is present at the beginning of electron beam melting. On the other hand, even after the decrease of carbon, the remaining oxygen can be removed by the suboxide evaporation.
With this process the high purity niobium in which both carbon and oxygen contents are reduced to a sufficient degree is obtainable by favorable conditions of reduction and melting.
