Study On The Mechanism Of Preparing Vanadium Nitride By Carbothermal Reduction Nitridatio

At present,the preparation of vanadium nitride by carbothermal reduction nitriding has problems such as high reaction temperature,high content of impurity elements and complicated process.Compared with the traditional vacuum carbothermal reduction nitriding method,this method combines the reduction and nitriding processes by reasonably controlling the partial pressure of nitrogen gas,and realizes the simultaneous reduction and nitriding reactions.This method can effectively reduce the reaction time and temperature,and can produce high quality vanadium nitride in a simple and efficient way.In this paper,a thermodynamic study of the chemical reactions involved in the preparation of vanadium nitride was first carried out.The results of the thermodynamic study show that reducing the system pressure during the carbothermal reduction reaction can promote the formation of VN and significantly reduce the chemical reaction temperature,and also promote the formation of intermediate by-products such as VC,V₂C and VO,which can easily react with nitrogen and be converted into vanadium nitride.Ab initio molecular dynamics（AIMD）simulations were used to elucidate the mechanism of the V₂O₃ carbothermal reduction-nitration reaction,and the results showed that the reduction and nitration reactions occur simultaneously during the reaction of vanadium trioxide to prepare vanadium nitride in the presence of N ₂.Meanwhile,C plays two important roles in the process of vanadi um trioxide carbothermal reduction nitration reaction.One role is that the presence of C can stabilize the adsorption of N₂ molecules on the V₂O₃-C surface,and has a catalytic effect on the N₂ molecules adsorbed on the C surface,prompting the activation and dissociation of N₂ molecules,thus promoting the formation of V-N bonds and the conversion of V₂O₃ to VN,and the activation and dissociation rates of nitrogen are the nitration rates The other role is to react with O in the V₂O₃ lattice and reduce V₂O₃.The results of thermodynamic calculations,ab initio molecular dynamics simulations and experimental studies show that:lowering the pressure of the reaction system is beneficial to promote the production of vanadium nitride,and the rate of nitridation of V₂O₃ can be increased by promoting the adsorption of N₂ and accelerating the dissociation rate of N₂;the experiments were carried out at a nitrogen pressure of 300 Pa,a carbon ratio of 0.25,a temperature of 1473 K and a holdin g time of 3h.High quality vanadium nitride was prepared.The vacuum one-step carbothermal reduction nitridation method was able to produce high quality vanadium nitride with shorter reaction time and lower temperature compared to the conventional carbothermal reduction nitridation method.