Effects of dilution and preheating on SHS of vanadium nitride

An experimental investigation of self-propagating high-temperature synthesis (SHS) of vanadium nitride (VN) was conducted with vanadium powder compacts in gaseous nitrogen. Effects of sample density, nitrogen pressure, diluent content, and sample preheating on the degree of conversion, flame-front velocity, and combustion temperature were studied. Experimental observations showed that the SHS process of the vanadium/nitrogen reaction was characterized by the steady propagation of a planar combustion front, followed by a prolonged afterburning reaction. The flame-front velocity increased with nitrogen pressure, but decreased with sample density. For the undiluted samples, a low degree of nitride conversion between 45 and 55% was obtained, primarily due to the formation of a liquid phase at nitrogen pressures higher than 0.79 MPa. The dilution of vanadium compacts with the nitride product VN powders suppressed the liquid formation, leading to a substantial increase in the degree of conversion. In addition, the conversion percentage of VN-diluted samples was further increased by properly preheating the sample prior to ignition. Under the condition with 30 wt.% dilution and preheating at 100–200 °C, it was found that a conversion over 90% was achieved. Based upon the XRD analysis, the δ-VN was identified as the dominant nitride phase synthesized in this study.