Research On High Quality Vanadium Nitride Synthesis Technology

Vanadium are widely used in aerospace,ships,metallurgy and marine engineering because of heavy corrosion-resistant,non-magnetic and other advantages.Vanadium may be translated into insoluble vanadium nitrides or vanadium carbides.The studies show that vanadium nitrides or vanadium carbides can improve steel general mechanical performance i.e anti-polish,anti-rust ability,toughness,intensity.But ordinary vanadium nitride has a lot of disadvantages such as low content of nitrogen and high content of oxygen and impurities which can not meet the requirements for automotive,aviation and other high-end industrial materials.This thesis is to preparation high quality vanadium with high nitrogen and low oxygen,which could meet the requirements of high performance material.Based on vanadium trioxide as raw material,powder carbide as reducing agent and ferric oxide as additives,in high temperature preparing high-quality vanadium nitride with high-energy ball milling and ordinary ball milling.According to the vanadium oxide reduction theory,vanadium trioxide was reduced to vanadium oxide and vanadium carbide under normal pressure after 1444.5K,.Vanadium carbide was nitrided into vanadium nitride were exothermic,and the reaction temperature of vanadium nitride by vanadium carbide was 1539.6K.Simply increasing temperature was not good for the nitriding reaction.Through thermodynamic calculation and phase diagram,the appropriate temperature and nitrogen flow rate were the important condition of the preparation of high quality vanadium nitride,and at the same time the reaction of the carbon monoxide and oxygen partial pressure can promote the reduction of nitride reaction.The research on kinetics indicates that no matter high-energy ball milling and ordinary ball milling that the main reaction temperature of nitride reaction was between 1000-1410C° during the reduction and nitride synthetic process,and with the increase of temperature,the exothermic reactions became more and more stronger,finally determining empirical formula of rate constants,reaction kinetics mechanism functions f(a)=(1-a),index pre-exponential factor(A)and kinetics equations.The experimental results indicates that the high-energy ball milling can effectively reduced the apparent activation energy of the material,which can promote the reduction of nitride reaction.With the increase of temperature,the index pre-exponential factor(A)increased,which indicates that the rate of reaction was mostly influenced by temperature at high temperature.The mixing mode,the nitrogen flow rate,the holding time,the carbon coefficient,additives,the high-energy ball milling time and so on,were studied,so the optimum nitride synthesis condition as following:high-energy ball milling 25min,nitrogen flow rate in 3.0L/min,nitride time 3h at 1643k,sinter time 1h at 1683k,the carbon coefficient 0.260 and 3%additives,the nitrogen,oxygen,carbon,phosphorus,sulfur content in high quality vanadium nitride are 16.8%,1.36%,1.82%,0.05%,0.09%.