稀土金属钆铽高纯化过程与机理研究

发布时间：2018-05-01 21:26

本文选题：稀土金属 + 高纯化　；参考：《北京科技大学》2016年博士论文

【摘要】：稀上金属在高新技术研发中发挥着重要作用,已成为不可或缺的新型战略资源。随着科技飞速发展,高强、高导和高纯稀土金属需求量大幅增加。我国稀土资源丰富,但每年高纯稀土金属的进口份额巨大。高纯稀土金属的制备存在方法单一、能源消耗大、成本高和产品纯度低等问题。为了解决上述问题,实现稀土资源高效、清洁化利用,开发新型的具有自主知识产权的高纯稀土制备工艺是现阶段我国稀土行业发展的重点之一。基于我国磁致伸缩和磁制冷材料领域对高纯稀土金属的迫切要求,本文围绕稀土金属钆和铽的高纯化展开研究。首先计算稀土元素钆、铽与典型杂质之间的相互作用力、吸脱附热以及动力学平衡参数,建立物化性质理论基础。针对性提出多种技术优化耦合的稀土纯化新工艺,建立其相应的优化流程。研究固溶、相变、磁搅拌等对提纯效果的影响,并数值模拟纯化过程。对纯化机理、杂质脱除机制及氧元素在稀土金属中的迁移行为等高纯化过程中的关键问题进行了探讨,为开发更为有效的稀土金属纯化新工艺提供了较为完整的理论依据和实验基础。主要研究结论包括：(1)基于现有等离子体电弧熔炼技术,将氢等离子体引入稀土金属纯化过程。结果显示,氢等离子体显著提高了金属钆和铽的纯化效果,成功制备出99.9840%高纯钆和99.9539%高纯铽。部分杂质金属元素可降低至10ppm以下,非金属杂质氧和氮含量均低于10ppm。研究发现,高温等离子体电弧中分解和激化的氢原子在纯化过程中发挥了重要作用,显著提高了杂质去除率。(2)采用FAST-2D与Stefan数值模拟技术,分别构建了自由燃烧电弧模型及稀土金属固液平衡体系。电弧温度场分布成典型钟铃形,且存在极大温度梯度,阳极附近电弧温度可达10000 K以上。等离子体流场在阴极附近存在阴极射流,速度最大值400m/s,可携带挥发的杂质元素进入气体相界层。熔融金属内中心部位温度可达5000 K,同时液相对流促进了杂质挥发。(3)耦合气固两步法对商用稀土金属钆和铽高纯化有显著效果。商用2N级稀土金属经高真空蒸馏之后纯度提高至4N,部分金属杂质元素含量降低至1 ppm以下。固相钙金属脱氧后,金属钆和铽内氧含量最低分别为3.6 ppm、 1.8ppm。对两步法耦合过程中杂质的脱除过程及杂质间相互钉扎作用进行了探讨。(4)利用氢原子较高的化学反应活性,将原位活性氢应用到稀士金属提纯中,对基体金属中的固溶氢脱除氧、氮等间隙杂质的过程和反应机理进行了研究。氢原子固溶于金属晶格内,会导致晶格膨胀。高真空加热后,固溶的氢原子与氧、氮元素在基体金属内发生反应,并以H20和NH3分子形式脱离,从而起到了除氧和除氮的作用。当金属基体内固溶有足量的氧时,氧元素和氮元素的去除率均可以达到80%。(5)氧元素作为稀土金属中最难脱除的杂质之一,其在金属中的迁移和反应过程引起了人们广泛的关注。本文采用同位素18O2作为示踪元素标定了金属铽内氧的迁移轨迹,探索金属铽氧化机理。氧化初期金属表面发生不均匀局部氧化,成核位置优先在金属缺陷处；随着氧化时间延长,形核长大并沿着金属晶粒边界和邻近区域加剧,发生晶间腐蚀,聚合相连而形成氧化物膜,氧扩散系数在1.4×10-19 m2/s与1.22×10-18 m2/s之间。
[Abstract]:Rare earth metals play an important role in the research and development of high technology. With the rapid development of science and technology, the demand for high strength, high conductivity and high purity rare earth metals has been greatly increased. The rare earth resources in China are rich, but the import of high pure rare earth metals is huge. First, high energy consumption, high cost and low purity of products. In order to solve the above problems, the high efficiency and clean utilization of rare earth resources and the development of new high purity rare earth preparation technology with independent intellectual property rights are one of the key points in the development of China's rare earth industry at the present stage. The urgent requirement of rare earth metals is to study the high purification of rare earth metal gadolinium and terbium. First, the interaction force between rare earth elements gadolinium, terbium and typical impurities, absorption and desorption heat and dynamic equilibrium parameters are calculated, and the theoretical basis of physical and chemical properties is established. The effects of solid solution, phase change and magnetic stirring on the purification effect were studied, and the purification process was simulated. The key problems in purification mechanism, impurity removal mechanism and the high purification process of oxygen elements in rare earth metals were discussed, which provided a more effective new process for the development of rare earth metal purification. The main conclusions are as follows: (1) the hydrogen plasma is introduced into the purification process of rare earth metals based on the current plasma arc smelting technology. The results show that the hydrogen plasma has significantly improved the purification effect of gadolinium and terbium, and 99.9840% high pure gadolinium and 99.9539% high pure terbium. The impurity metal elements can be reduced to less than 10ppm and the content of oxygen and nitrogen of non-metallic impurities is lower than that of 10ppm.. The decomposition and intensification of hydrogen atoms in the high temperature plasma arc played an important role in the purification process and significantly improved the removal rate of impurities. (2) free combustion was constructed by using the numerical simulation technology of FAST-2D and Stefan. Arc model and the solid liquid equilibrium system of rare earth metals. The distribution of arc temperature field is a typical bell shape, and there is a great temperature gradient. The arc temperature near the anode is up to 10000 K. The plasma flow field has a cathode jet near the cathode, the maximum velocity is 400m/s, which can carry the volatile impurity elements into the gas phase boundary layer. The molten metal inside the molten metal is inside. The temperature of the center is up to 5000 K, and the liquid convection promotes the volatilization of impurities. (3) the coupling gas solid two step method has significant effect on the high purification of commercial rare earth metal gadolinium and terbium. The purity of commercial 2N grade rare earth metal is increased to 4N after high vacuum distillation, and the content of some metal impurity elements is reduced to less than 1 ppm. The lowest internal oxygen content of gadolinium and terbium is 3.6 ppm respectively. The removal of impurities in the two step process and the interaction of impurities in the two step process are discussed. (4) using the high chemical reaction activity of the hydrogen atom, the in-situ active hydrogen is applied to the dilute metal purification, and the solid solution hydrogen deoxidization and nitrogen gap impurities in the matrix metal are removed. The process and reaction mechanism are studied. Hydrogen atoms dissolve in the lattice of metal and cause the lattice expansion. After high vacuum heating, the solid solution of hydrogen atoms react with oxygen and nitrogen in the matrix metal and disengage in the form of H20 and NH3 molecules, thus acting as deoxidizing and denitrification. When a full amount of oxygen is dissolved in the metal matrix, The removal rate of oxygen and nitrogen can both reach 80%. (5) as one of the most difficult removal of impurities in rare earth metals. The migration and reaction process in metals have aroused widespread concern. This paper uses isotopic 18O2 as a tracer element to calibrate the migration path of the internal oxygen of metal terbium and explore the oxidation mechanism of metal terbium. Inhomogeneous partial oxidation of metal surface occurred at the initial stage, and the nucleation position preceded the metal defect. With the prolonged oxidation time, the nucleation grew up and intensified along the grain boundaries and adjacent regions. Intergranular corrosion occurred and the polymerization was connected to form oxide films. The oxygen diffusion coefficient was between 1.4 * 10-19 m2/s and 1.22 * 10-18 m2/s.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.45

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