【作者】 张宇；

【导师】 吕学伟；

【作者基本信息】 重庆大学 ， 冶金工程（专业学位）， 2019， 硕士

【摘要】 氮化钛是一种具有诸多优良性能的材料,例如熔点和硬度高、导电性和导热性优良、耐腐蚀和磨损性好,因而在金属陶瓷、高温涂层、电子领域等有广泛应用。但就目前而言,氮化钛的商品化应用程度并不高,限制其应用的主要因素就是生产成本问题。目前,工业上大规模生产氮化钛粉末的方法有钛粉和氢化钛粉的氮化法,其他方法暂时还不能进行规模化生产,而Ti/TiH₂价格昂贵,也限制了其进一步发展。因此,研究出切实可行且生产成本低的氮化钛粉末制备方法具有重要意义。本文提出一种基于氨气直接还原氮化二氧化钛制备氮化钛的新方法,以NH₃作为还原剂和氮源,借助气固相反应速率快的优点,实现低温快速制备TiN粉末。论文首先通过热力学计算软件（FactSage 6.2）查明了二氧化钛还原氮化的热力学规律。具体研究了TiO₂-NH₃体系里不同气体成分对TiO₂的还原和氮化效果,热力学平衡表明,NH₃在高温下会发生分解,分解的H₂在温度低于1773K以下只能将TiO₂还原至Ti₃O₅,而N₂无法氮化钛氧化物。在氨气还原氮化TiO₂的过程中,固体产物可能分为三种,低价钛氧化物,钛氧化物和氮化钛的混合物以及纯氮化钛,增大NH₃比例可以得到高纯度的氮化钛,在较低温度下增大氨气比例可以不经过中间氧化物而得到氮化钛。其次研究了热还原氮化工艺中的物相转变规律,研究了NH₃高温分解行为,1000℃下NH₃分解比例为60%,实际气体成分中H₂体积百分比为56.3%,N₂占比18.8%,残留NH₃占比24.9%。研究了H₂:N₂摩尔比3:1时对TiO₂的还原氮化效果,1200℃时该比例的混合气体只能够将TiO₂还原至Ti₄O₇,在1400℃下,H₂只能够将TiO₂还原至Ti₃O₅,N₂不能够将钛氧化物氮化为TiN。通过XRD分析测试手段研究了二氧化钛的物相转变历程,不同温度下氨气还原氮化TiO₂的反应路径不同,在1000℃及以下温度,TiO₂的转变路径为TiO₂→TiN→Ti（N,O）,在温度高于1000℃时,TiO₂被还原后氮化,转变路径为TiO₂→Ti_nO_2n-1→TiN→Ti（N,O）,不同温度下的还原程度不同,在试验结果中,1100℃下为Ti₄O₇,1200℃下为Ti₃O₅,温度越高,钛的价态越低。最后,对氨气热还原氮化法制备氮化钛的工艺进行了深入研究,探查了不同工艺制度（焙烧温度、焙烧时间、氨气流量等）对氮化钛粉末制备的影响,研究结果表明,反应温度和还原氮化时间对NH₃的还原氮化效果影响明显,提高温度和延长时间都有助于降低产物中的O含量;试验条件下最优的工艺参数为NH₃流量为150ml/min时在1200℃反应8h,此时样品中的O含量为0.51%,初步推测其TiN含量超过99%,达到实验室药品分析纯的纯度。本课题具有较好的前瞻性和探索性,为制备高纯度的、粒度分布窄的和细粒径的TiN粉末提供了新的技术路线,具有应用价值。更多还原

【Abstract】 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.更多还原