Study On The Preparation Process Of Titanium Nitride By Thermal Reduction With Ammonia

Titanium nitride is a material with many excellent properties,such as high melting point and hardness,excellent electrical and thermal conductivity,good corrosion resistance and wear resistance,and thus has wide applications in cermet,high temperature coatings,and electronics.However,for the moment,the commercialization of titanium nitride is not high,and the main factor limiting its application is the cost of production.At present,the industrial method for large-scale production of titanium nitride powder is a method of nitriding titanium powder and titanium hydride powder.Other methods are not yet capable of large-scale production,and Ti/TiH₂ is expensive,which limits its further development.Therefore,it is of great significance to study a preparation method of titanium nitride powder which is practical and low in production cost.In this paper,a new method for the preparation of titanium nitride by direct reduction of titanium dioxide with ammonia is proposed.NH₃ is used as a reducing agent and a nitrogen source,and the TiN powder can be rapidly prepared at a low temperature by virtue of the fast gas-solid phase reaction rate.Firstly,the thermodynamic calculation software?FactSage 6.2?was used to find out the thermodynamics of titanium dioxide reduction and nitridation.The effects of different gas compositions on the reduction and nitridation of TiO₂ in TiO₂-NH₃ system were studied.The thermodynamic equilibrium indicated that NH₃ would decompose at high temperature.The decomposed H₂ could only reduce TiO₂ to Ti₃O₅ below 1773K,while N₂ cannot nitride titanium oxide to TiN.In the process of ammonia reduction of nitriding TiO₂,the solid products may be classified into three types,low-valent titanium oxide,a mixture of titanium oxide and titanium nitride,and pure titanium nitride.By increasing the NH₃ ratio,high-purity titanium nitride can be obtained,and the ammonia gas ratio can be increased at a lower temperature to obtain titanium nitride without passing through the intermediate oxide.Secondly,the phase transition law in the thermal reduction nitridation process was studied.The high temperature decomposition behavior of NH₃ was studied.The decomposition ratio of NH₃ at 1000? was 60%,the volume fraction of H₂ in the actual gas composition was 56.3%,the ratio of N₂ was 18.8%,and the ratio of residual NH₃was 24.9%.The reduction and nitridation effect of TiO₂ at a molar ratio of H₂:N₂ of 3:1was studied.At 1200?,the mixed gas of this ratio can only reduce TiO₂ to Ti₄O₇.At1400?,H₂ can only reduce TiO₂ to Ti₃O₅.N₂ is not capable of nitriding titanium oxide to TiN.The phase transition history of titanium dioxide was studied by XRD analysis.The reaction path of TiO₂ for ammonia reduction at different temperatures was different.At 1000?and below,the transition path of TiO₂ was TiO₂?TiN?Ti?N,O?.When the temperature is higher than 1000?,TiO₂ is reduced and nitrided,and the transition path is TiO₂?Ti_n O_2n-1?TiN?Ti?N,O?.The degree of reduction at different temperatures is different.In the test results,Ti₄O₇ is obtained at 1100? and Ti₃O₅ at 1200?.The higher the temperature,the lower the valence state of titanium.Finally,the process of preparing titanium nitride by ammonia reduction nitriding method was studied in depth,and the effects of different process regimes?baking temperature,calcination time,ammonia flow rate,etc.?on the preparation of titanium nitride powder were investigated.The results show that the reaction temperature and reduction nitriding time have obvious effects on the reduction and nitridation of NH₃.The increase of temperature and prolongation time can help to reduce the O content in the product.The optimum process parameters under the test conditions are as follows:the NH₃ flow rate is 150ml/min and the reaction is carried out at 1200? for 8h.At this time,the O content in the sample is 0.51%.It is presumed that the TiN content exceeds99%,which is the purity of the laboratory analytical reagent.The subject has good prospective and exploratory properties,and provides a new technical route for the preparation of high-purity,narrow particle size distribution and fine particle size TiN powder,and has application value.