本文選題：稀土金屬 + 高純化��； 參考：《北京科技大學(xué)》2016年博士論文

【摘要】：稀上金屬在高新技術(shù)研發(fā)中發(fā)揮著重要作用,已成為不可或缺的新型戰(zhàn)略資源。隨著科技飛速發(fā)展,高強(qiáng)、高導(dǎo)和高純稀土金屬需求量大幅增加。我國稀土資源豐富,但每年高純稀土金屬的進(jìn)口份額巨大。高純稀土金屬的制備存在方法單一、能源消耗大、成本高和產(chǎn)品純度低等問題。為了解決上述問題,實現(xiàn)稀土資源高效、清潔化利用,開發(fā)新型的具有自主知識產(chǎn)權(quán)的高純稀土制備工藝是現(xiàn)階段我國稀土行業(yè)發(fā)展的重點之一�；谖覈胖律炜s和磁制冷材料領(lǐng)域?qū)Ω呒兿⊥两饘俚钠惹幸?本文圍繞稀土金屬釓和鋱的高純化展開研究。首先計算稀土元素釓、鋱與典型雜質(zhì)之間的相互作用力、吸脫附熱以及動力學(xué)平衡參數(shù),建立物化性質(zhì)理論基礎(chǔ)。針對性提出多種技術(shù)優(yōu)化耦合的稀土純化新工藝,建立其相應(yīng)的優(yōu)化流程。研究固溶、相變、磁攪拌等對提純效果的影響,并數(shù)值模擬純化過程。對純化機(jī)理、雜質(zhì)脫除機(jī)制及氧元素在稀土金屬中的遷移行為等高純化過程中的關(guān)鍵問題進(jìn)行了探討,為開發(fā)更為有效的稀土金屬純化新工藝提供了較為完整的理論依據(jù)和實驗基礎(chǔ)。主要研究結(jié)論包括：(1)基于現(xiàn)有等離子體電弧熔煉技術(shù),將氫等離子體引入稀土金屬純化過程。結(jié)果顯示,氫等離子體顯著提高了金屬釓和鋱的純化效果,成功制備出99.9840%高純釓和99.9539%高純鋱。部分雜質(zhì)金屬元素可降低至10ppm以下,非金屬雜質(zhì)氧和氮含量均低于10ppm。研究發(fā)現(xiàn),高溫等離子體電弧中分解和激化的氫原子在純化過程中發(fā)揮了重要作用,顯著提高了雜質(zhì)去除率。(2)采用FAST-2D與Stefan數(shù)值模擬技術(shù),分別構(gòu)建了自由燃燒電弧模型及稀土金屬固液平衡體系。電弧溫度場分布成典型鐘鈴形,且存在極大溫度梯度,陽極附近電弧溫度可達(dá)10000 K以上。等離子體流場在陰極附近存在陰極射流,速度最大值400m/s,可攜帶揮發(fā)的雜質(zhì)元素進(jìn)入氣體相界層。熔融金屬內(nèi)中心部位溫度可達(dá)5000 K,同時液相對流促進(jìn)了雜質(zhì)揮發(fā)。(3)耦合氣固兩步法對商用稀土金屬釓和鋱高純化有顯著效果。商用2N級稀土金屬經(jīng)高真空蒸餾之后純度提高至4N,部分金屬雜質(zhì)元素含量降低至1 ppm以下。固相鈣金屬脫氧后,金屬釓和鋱內(nèi)氧含量最低分別為3.6 ppm、 1.8ppm。對兩步法耦合過程中雜質(zhì)的脫除過程及雜質(zhì)間相互釘扎作用進(jìn)行了探討。(4)利用氫原子較高的化學(xué)反應(yīng)活性,將原位活性氫應(yīng)用到稀士金屬提純中,對基體金屬中的固溶氫脫除氧、氮等間隙雜質(zhì)的過程和反應(yīng)機(jī)理進(jìn)行了研究。氫原子固溶于金屬晶格內(nèi),會導(dǎo)致晶格膨脹。高真空加熱后,固溶的氫原子與氧、氮元素在基體金屬內(nèi)發(fā)生反應(yīng),并以H20和NH3分子形式脫離,從而起到了除氧和除氮的作用。當(dāng)金屬基體內(nèi)固溶有足量的氧時,氧元素和氮元素的去除率均可以達(dá)到80%。(5)氧元素作為稀土金屬中最難脫除的雜質(zhì)之一,其在金屬中的遷移和反應(yīng)過程引起了人們廣泛的關(guān)注。本文采用同位素18O2作為示蹤元素標(biāo)定了金屬鋱內(nèi)氧的遷移軌跡,探索金屬鋱氧化機(jī)理。氧化初期金屬表面發(fā)生不均勻局部氧化,成核位置優(yōu)先在金屬缺陷處；隨著氧化時間延長,形核長大并沿著金屬晶粒邊界和鄰近區(qū)域加劇,發(fā)生晶間腐蝕,聚合相連而形成氧化物膜,氧擴(kuò)散系數(shù)在1.4×10-19 m2/s與1.22×10-18 m2/s之間。
[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.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG146.45

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