Thermotransport of carbon in niobium

The thermotransport behavior of carbon in niobium metal was investigated in the one-phase and two-phase conditions using radioactive tracer techniques. Experiments were performed in a differentially ion-pumped system at pressures of about 3 X10-9 Torr. The heat of transport for carbon in niobium in the one-phase condition is -13.1+-0.6 kcal mol-1 and that for specimens partly in the two-phase condition is -13.3+-1.0 kcal mol-1. Experiments that were carried out in an inert gas atmosphere and under pressures of 10-6 Torr in a system using an oil diffusion pump showed an initial decarburization of the specimen followed by carburization during continued heating. Themotransport experiments in an inert gas atmosphere gave anomalous results indicating carbon transport towards the colder regions. This effect is attributed to a vapor phase transport. (Auth.)