Abstract
Using the vacuum process, carbide reduction of niobium pentoxide due to the following reaction was investigated experimentally : Nb2O5+5NbC=7Nb+5CO. The mixing ratio of Nb2O5/NbC was varied from 33/67 to 45/55. By means of fluctuation measurements of pressure and temperature, it was clarified that the reaction began to proceed rapidly above 1700°C. Crude niobium metal, containing 96 to 97%Nb, was obtained easily by this process. The purification of crude niobium metal obtained above was examined in a series of vacuum refining experiments. Impurities, such as carbon, oxygen and nitrogen in niobium metal decreased at the refining temperature above 2150°C at the pressure of 10−5 mmHg. The removal of carbon during refining process was dependent on both temperature and oxygen content. Rapid removal of oxygen was observed in the presence of carbon. Cold-rolling was attempted on each specimen of refined metals, and fabricable specimens containing above 99.7%Nb showed the Vickers hardness lower than 200.
