Preparation of VN via core-shell precursor method under the intervention of dispersants
In this study,polyvinyl pyrrolidone(PVP)is used to optimize the core-shell V@C precursor structure,and the precursor is heat-treated to obtain vanadium nitride(VN)up to the National Standard VN 16 grade of China.The addition of PVP promotes both the uniform dispersion of the carbon powders in the vanadium rich solution and facilitates the hydrogen bonding of ammonium polyvanadate(APV)ions,which are adsorbed on the surface of carbon powders for nucleation and growth.The as-prepared precursor by adding PVP has better encapsulated and stable carbon powder core and APV shell with uniform and moderate thickness,as well as small and homogeneous particle size distribution.In the ni-tridation and reduction process,the phase transition from precursor to VN is as follows:APV → V2O5→ V6O13 → V7O13 → VO2 → V3O5 → V2O3 →(VC)→ VN.Due to its more stable core-shell coating structure and more uniform particle size distribution,the optimized precursor forms a more stable phase reaction interface and more active reaction sites,which reduces the reaction activation energy(Ea)at each stage,and makes it more efficient in reducing and nitriding and easier to transition to low-valent VOx and VN.In comparison with current carbothermal reduction process,the reaction time is shortened by 75％,and the flow rate of N2 is reduced from 300 mL/min to 200 mL/min,the usage of N2 is reduced by 40％,significantly reducing production costs.
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