| Vanadium nitride is an important alloy additive in high-strength microalloy steel,it has a beneficial effect on fine grain strengthening and precipitation strengthening which can improve the comprehensive performance of steel.Adding vanadium nitride to steel can save the amount of vanadium to reduce the cost in smelting process.At present,the main method to prepare vanadium nitride in China is heating a mixture of V2O5 and carbon powder under a flowing nitrogen atmosphere under normal pressure at high temperature.However,the vanadium pentoxide is the breakdown product of ammonium ployvanadate.So it can shorten and simplify the process by preparing vanadium nitride using ammonium ployvanadate directly.Besides,NH3,which is the breakdown product of ammonium ployvanadate,can be used as reductant during ammonium ployvanadate carbon thermal reduction reaction.Then,the consumption of graphite and production cost can be reduced.The resource of graphite can be saved.The paper mainly studied the technology to prepare VN by carbon-thermal reducting and nitriding ammonium ployvanadate and analyzed the factors which influence the composition and proterty of vanadium nitride.The dynamical behavior and reaction mechanism of the process of synthesizing VN was studied by TGA.Conclusions are as follows:(1)According to the analysis of TG and DSC,when the temperature is increasing,ammonium ployvanadate will dehydration and deamination under atmospheric pressure.At 100℃,ammonium ployvanadate lost a lot of water.When the temperature rised to 320℃,ammonium ployvanadate started to deaminase and completed at 425℃.(2)Experimental results showed that,with the increasing of C/O,the carbon content increased,the vanadium content increased at first,then decreased,nitrogen content decreased.Vanadium content of reduction products got maximum when the C/O was 0.95 and carbon content slightly becomed smaller,the product of nitrogen content was slightly larger.With the increase of nitriding temperature,vanadium content and nitrogen content increased after decreased firstly,carbon content after the first sharp decreased largely,then stayed unchanged.Increasing the nitriding time and the nitrogen flow can contribute to the decrease of carbon content,increase of vanadium content and nitrogen content.(3)According to the analysis of the XRD of products at different temperatures and TG under different atmospheres,the ammonium ployvanadate carbothermal reduction was a step-by-step process,the reaction is:at 320℃,ammonium ployvanadate decomposed into V2O5.At 360℃ V2O5 was reduced into V6O13.At 450℃,V6O13 was reduced into V2O4.At 67℃,V2O4 was reduced into V6O11.At 930°C,V6011 was reduced into V2O3.And at 1000℃C,VC was generated,.At 1275℃,VC was changed into VN;(4)Ammonium polyorthovanadate carbothermal reduction and nitriding using reaction kinetics mechanism nonisothermal analysis level is reasonable.It fits straightly good linearity and the correlation coefficient of linear fit is over 0.989.Carbon thermal reduction nitriding process dynamics analysis calculated 1062-1309℃ activation energy of 77.461 kJ mol-1,The activation energy of 1310-1440℃158.175 kJ mol-1.Nitriding temperature has more impact on product ingredients.With the increasing nitriding temperature,vanadium content and nitrogen content increases at first and then decreases.Basically unchanged after reducing the carbon content of the first violent,however,it is an opposite trend to nitrogen content.When the temperature exceeds 1400℃,nitride vanadium content and nitrogen content reduced significantly.At this time,VN became VC and decreased the nitrogen content.Preparation of ammonium vanadate vanadium nitride process is simple.Shorter process and less consumption of graphite is the advantadge of the meheod.Besides,vanadium,nitride and carbon content of the vanadium nitride comply with national standards.So using ammonium ployvanadate to prepare vanadium nitride could be applied. |
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