Research On Preparing Vanadium Nitride From V₂O₅with Reduction And Nitridation By One-step Method

Vanadium nitride is an important alloy additive in high-strength micro-alloyde steel,and it has an beneficial effect on fine grain strengthening and precipitation strengtheningto improve comprehensive performance of steel, and adding vanadium nitride to steel cansave the amount of vanadium to reduce the cost of smelting process, meanwhile,Chinahas abundant resoueces of vanadium-bearing shale.Preparing VN from V2O5extractedfrom low-grade shale can not only improve the the comprehensive utilization ofvanadium resource, but also provide excellent quality materials with competitive pricefor micro-alloyed technology in metallurgical industry. Thus, It is necessary to study theeconomic and efficient VN preparation process.The paper mainly studies VN preparation technology from V2O5extracted fromlow-grade and vanadium-bearing shale with reduction and nitridation by one-stepmethod, and analyzes the factors which influence the composition and proterties ofvanadium nitride. The dynamical behavior and reaction mechanism of the process ofsynthesizing VN by one-step method was studied by TGA.Based on thermodynamic analysis, V2O5carbon thermal reduction is step-by-stepprocess, and V2O5can be reduced firstly, and VO is the most difficultly to be reduced.V2O5can be reduced to low-valence vanadium oxides with low-smelting point below670℃. When the temperature is over910℃, the reduction and nitridation reaction couldbe simultaneous. In actual reaction process, the partial pressure of the gas in system hasan impact on the specific transition temperature of reduction and nitridation reaction.In order to meet performance requirements of VN, It is necessary to select pelletspreparaed by high pressure ball machine as raw materials. The reasonable samplepreparation process is determined by pellets forming experiment.The pre-reduction temperature has an impact on the composition and performanceof products, and it is reasonable to take650℃holding for4h as the best pre-reductionconditions of650℃. The nitrogen content of nitridation products will reduce when thecarbon ratio increases, the proper carbon ratio is0.33. As the reaction temperatureincreases, the carbon content of nitridation products decreases rapidly and nitrogencontent increases gradually, and N content can reach to15.72%at1500℃. Thenitridation products is tested with minimal VN after holding4hours at1000℃,and thephase composition of products is VN when the reaction temperature is1300～1500℃.Compared to the pellets before the nitridation reaction, the volume of pellets will shrink after the reaction, and the density will increase.The dynamical behavior of the process of synthesizing VN by one-step method wasstudied by TGA. N2only plays a role of protective atmosphere below800℃, which is thesame as Ar. The weight loss percentage under N2are larger than that of Ar at800℃, andthe weight loss will continue to increase with temperature increasing. It is found that N2is beneficial to stimulate reduction and carbonization reaction to proceed. It is reasonableto use first order reaction kinetic mechanism function to analyze V2O5reduction andnitridation process by non-isothermal thermogravimetry, and the fitting straight lineshave good linear, and all of the correlation coefficients of lines are over0.989. Theactivation energy of preparing VN from V2O5with reduction and nitridation by one-stepmethod is104.005/KJ mol-1and the frequency factor is470.52when the reactiontemperature is at997~1085℃, and the activation energy and frequency factor is150.052/KJ mol-1and2.35×104respectively at1085~1153℃.