The investigations of the reduction of niobium pentoxide by carbon showed that niobium metal could be prepared by a direct reduction. High temperatures in the region of 2000°C but below the melting point of niobium and dynamic vacuum of one micron or less were the principal experimental conditions employed throughout the course of this study. The reaction, which followed very closely the stoichiometry of the equation Nb2o5 +5C ---> 2Nb + 5CO, began at a temperature near 1200°C and was nearly completed at 1600°C. The data indicated that it might be possible to allow reduction to take place at approximately 1800°C. After the reaction is completed at this temperature, raising of the temperature of the reaction material to nearly 2000°C might eliminate residual oxygen as a result of volatilization of a lower oxide of niobium.
Stevens, Ernest Roger and Wilhelm, H. A., "Reduction of niobium pentoxide by carbon" (1961). Ames Laboratory Technical Reports. 45.