Abstract
Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V 2O 5 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, V 6O 13, V 2O 4, VO 2, V 2O 3, 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 m 2g −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.
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