Reactions of Compounds in the Nb-C-O System with CO or CO2

Reactions of compounds in the Nb-C-O system with CO or CO2 were investigated. Reactions of solid phases, such as Nb, NbO, NbC and Nb2O5, with CO, CO2 or a mixture gas of CO and CO2, up to 1400°C were studied by the measurement of weight changes, X-ray analysis and chemical analysis. In the reactions of Nb or NbO with CO, mixtures of NbO2 and NbC were obtained as final products according to the following gross reactions: 3Nb+2CO→2NbC+NbO2…(4) and 3NbO+CO→2NbO2+NbC…(2). In the case of Nb2O5 with CO, NbO2 was obtained as a reduction product by the following equation, Nb2O5+CO→2NbO2+CO2…(3). Little weight change was observed in the reaction of NbC with CO. CO2 acts as an oxidizing agent and Nb2O5 was obtained in all cases with the CO2 reaction.Carbon and oxygen increased during the arc melting process in CO atmosphere in the specimen containing more than 80 at% niobium. Excepting the above case, carbon and oxygen were found to decrease in most specimens during the arc melting process in CO or Ar atmosphere, and the rate of decrease is remarkable in the specimens containing oxygen and carbon at the ratio of about one to one.