Study on the preparation of high quality VN-19 and the mechanism of its isothermal kinetic

Abstract

In this study, high-quality VN (VN-19 level) was synthesized and the reaction kinetics were explored through isothermal kinetic analysis firstly. After a series of optimization experiments, the mild atmospheric-pressure conditions for synthesizing VN were as follows: nitrogen flow rate of 160 mL/min, holding temperature of 1450 ℃ and holding time of 0.5 h without requiring high-pressure equipment but shortening reaction time. Under this conditions, the nitrogen content of the product was 18.69 wt%, reaching the highest quality VN-19 level (18-20 wt%) defined in GB/T 20567-2020. The first-reported isothermal kinetic analysis revealed three distinct reaction stages with characteristic activation energies: 1) interface chemical reaction rate control stage; 2) mixing rate control stage; 3) diffusion rate control stage. The activation energies (Ea) of the three stages were 79.8570, 62.9511 and 72.5923 kJ/mol, respectively. The reaction rate constant showed increasing sharply at beginning and then gradually tending to become flat. This work provided a fundamental kinetic insight that advanced the understanding of transition metal nitride formation mechanisms.