PREPARATION AND CHARACTERIZATION OF EARLY TRANSITION-METAL CARBIDES AND NITRIDES

Temperature-programmed synthesis in a flowing reactive gas stream is used to prepare transition-metal carbides and nitrides from groups IVB-VIB in high surface area form. The materials are characterized by X-ray diffraction, elemental analysis, thermogravimetric analysis, temperature-programmed reduction, selective chemisorption of carbon monoxide, and surface area measurements. It is deduced that the space velocity of the synthesis gas is an important factor in obtaining high surface area. Activation energies for the synthesis , calculated from the reaction temperature profiles, yield values close to those for the diffusion of oxygen in the oxides. The synthesis temperature is found to correlate with the melting point of the parent oxides. These results indicate that a critical step in the synthesis involves disruption of metal-oxygen bonds.