Preparation and Characterization of Niobium Carbide and Carbonitride

Abstract

Unsupported niobium carbide powders of NbC were prepared by carburization of commercial niobium pentoxide in flowing CH4–H2mixtures. Several routes of synthesis were investigated, leading to final carbides with specific surface areas ranging from 10 to 50 m2g−1. During direct carburization, after the first step of reduction of Nb2O5to NbO2, a long induction period which was succeeded by an acceleratory period, was observed for the reduction/carburization to NbC. In the presence of a catalyst of methane decomposition, this induction period was eliminated but the superficial carbon free contamination of the final carbide was increased. However, this contamination can be removed by a reducing treatment and CO chemisorption can be observed. The preparations through niobium oxynitride lead to face-centered cubic carbonitrides with specific surface areas ranging from 27 to 49 m2g−1. Chemical composition and cell parameter of these cabonitrides vary slightly with the synthesis conditions. After a reducing treatment, as for NbC, CO chemisorption was also observed.