Preparation and characterization of niobium carbide and carbonitride

Unsupported niobium carbide ponders of NbC were prepared by carburization o f commercial niobium pentoxide in flowing, CH4-H-2 mixtures. Several routes of synthesis were investigated, leading to final carbides with specific su rface areas ranging from 10 to 50 m(2)g(-1). During direct carburization, a fter the first step of reduction of Nb2O5 to NbO2, a long induction period which was succeeded by an acceleratory period, was observed for the reducti on/carburization to NbC. rn the presence of a catalyst of methane decomposi tion, this induction period was eliminated but the superficial carbon free contamination of the final carbide was increased. However, this contaminati on can be removed by a reducing treatment and CO chemisorption can be obser ved. The preparations through niobium oxynitride lead to face-centered cubi c carbonitrides with specific surface areas ranging from 27 to 49 m(2) g(-1 ). Chemical composition and cell parameter of these cabonitrides vary sligh tly with the synthesis conditions. lifter a reducing treatment, as for NbC, CO chemisorption was also observed. (C) 1999 Academic Press.