SYNTHESIS OF HIGH SURFACE-AREA VANADIUM NITRIDE

Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V2O5 by gaseous ammonia. The reaction was followed by monitoring gas phase reaction products by on-line mass spectroscopy. X-ray diffraction and elemental analysis were used to identify various solid-state reaction intermediates, V6O13, V2O4, VO2, V2O3, and VO, and to establish that the final reaction step was the nitridation of VO to VN. Heating rate had a substantial effect on product specific surface area and a rate of 0.083 K sec-1 resulted in an optimal value of 90 m2g-1. The activation energy for nitridation was not constant, but rose from 203 to 243 kJ mol-1 as the extent of reaction increased from 0.25 to 0.75. The transformation was limited by the bulk diffusion of oxygen and nitrogen and not by a surface process. © 1992 Academic Press, Inc.