铈基稀土抛光粉氟化行为的第一性原理研究

发布时间：2018-03-18 06:45

本文选题：氟化　切入点：二氧化铈　出处：《北京化工大学》2017年博士论文　论文类型：学位论文

【摘要】：稀土作为战略性资源重要性堪比石油,内蒙古包头市具有全球最大的白云鄂博轻稀土矿,该矿中约含50%的铈。作为铈元素的原料和加工基地,包头近年来出现了多家铈基稀土抛光粉企业,开辟了一个轻稀土新材料应用领域。由于CeO_2表面活性高、极易团聚、颗粒形貌不规则,不能直接用于精密抛光。目前市售铈基抛光粉大多进行氟化处理,该工艺是向氧化铈前驱体中加入氟化剂,如氢氟酸、氟硅酸、氟化铵或氟化钠等进行氟化反应。实验表明,氟化铈基抛光粉的颗粒形貌由棒状或片状等变为(类)球形,团聚显著地减弱,提高了被抛光件表面光洁度。为研究铈基稀土抛光粉中氟行为的作用机理,本文采用第一性原理方法,研究了氟化氧化铈体相和表面的稳态结构,氟化氧化铈晶体对机械抛光性能的影响,氟对氧化铈抛光粉晶体形貌的影响,氧化铈氟化过程的控制因素。氟原子在化学抛光氧化硅玻璃中的作用。从电子结构角度分析了氟化对体相的宏观力学性能和表面的表面能影响的内在原因。给出铈基复合抛光粉的最佳氟含量,为开发高端铈基抛光粉提供理论依据。主要工作如下:1、常压及外压下CeO_2力学性能和电子结构分析。通过计算结合能与弹性常数,判断常压下CeO_2力学稳定性;计算CeO_2的体积模量、剪切模量、杨氏模量、维氏硬度,并与实验结果进行比较。分析外压低于30 GPa时,CaF2结构的CeO_2力学和动力学稳定性,弹性模量、硬度、韧性和各向异性随压力的变化。引入Hubbard U参量修正Ce4f层电子的强关联效应,分析CeO_2态密度和电荷密度分布,了解外压下Ce离子和O离子电子态分布及成键的变化,深入理解力学性能改变原因。2、氟化对CeO_2力学性能和电子结构影响。考察氟掺杂三种可能位置的总能,计算掺杂形成能,确定氟改性CeO_2的稳态结构。研究六种氟掺杂量时CeO_(2-x)F_x的弹性力学性能,分析弹性模量、硬度、韧性和各向异性随氟含量的变化,确定保持机械抛光性能的氟含量。计算四种氟掺杂体系CeO_(2-x)F_x的态密度和电荷密度分布,分析了 F离子与Ce、O离子分波态密度的相互作用,阐明氟原子及其掺杂量对CeO_2弹性力学性能的影响机理。研究了 CeC1.75F0.25体系的弹性力学性能和电子结构在抛光外压力下的变化。3、CeO_2的氟化及对晶体形貌影响。构建并弛豫计算CeO_2(111)表面、CeO_2(100)和(110)重构表面的总能,比较三种表面的表面能,并与其他文献的计算值和实验值相比较。计算F单原子在三种表面的吸附势能面,确定稳定吸附构型,比较吸附F原子后三种表面的表面能,预测了抛光粉晶粒的最终形貌。研究不同F原子覆盖度下(111)和(100)面的表面能差对晶体形貌的影响。计算表层及次表层氧空位形成能,研究F原子从(100)表面迁入表层氧空位,并进一步迁入次表层氧空位的迁移激活能,确定F原子从表面向体内扩散的控制因素。研究CeO1.75F0.25体系的(111)和(100)表面的电子结构,确定氟对表面的Ce-O成键、总能和表面能的影响。4、氟化铈基抛光粉的抛光反应过程。构建CeO_2(111)和CeO1.75F0.20(100)两种磨削表面,计算SiO_2晶粒在两种表面的吸附能,确定稳定的初态始构型。详细研究两种表面磨削SiO_2晶粒的反应过程,分析Si原子成键、断键的演变情况,判断氟元素在化学抛光中的作用。
[Abstract]:Rare earth as a strategic resource in Baotou city of Inner Mongolia as the importance of oil, has the world's largest Baiyunebo light rare earth ore, the ore contains about 50% CE. As cerium raw materials and processing base, Baotou in recent years, there have been a number of ceria based polishing powder enterprises, opened up a new field of application of light rare earth materials because. CeO_2 has high surface activity, easy agglomeration, particle morphology is irregular, cannot be directly used for precision polishing. Currently commercially available cerium based polishing powder mostly fluoride treatment, this is the process of adding fluoride to cerium oxide precursor, such as hydrofluoric acid, fluoride, fluoride reaction of ammonium fluoride or sodium fluoride and other experiments. Show that the particle morphology of fluoride cerium based polishing powder by rod or flake into spherical agglomeration (class), significantly reduced, increased by polishing the surface finish. A mechanism for fluoride behavior of ceria based polishing powder. In this paper, by using the first principle method, studied the steady structure of fluoride cerium oxide and cerium oxide on the surface of the effect of fluoride crystals on mechanical polishing properties. The effects of fluoride on cerium oxide polishing powder crystal morphology, the controlling factors of cerium oxide fluorination process. Effect of fluorine atoms in chemical polishing of silicon oxide in the glass were analyzed. Effect of fluoride on the body internal cause of macro mechanical properties and the surface energy of the electronic structure from the point of view. The best content of fluorine given cerium based composite polishing powder, to provide a theoretical basis for the development of high-end ceria based polishing powder. The main work is as follows: 1, analysis of mechanical properties and electronic structure of CeO_2 under normal pressure and external pressure. By calculating the binding energies and elastic constants, CeO_2 mechanical stability under atmospheric pressure; calculation of CeO_2 bulk modulus, shear modulus, Young's modulus, Vivtorinox hardness, and compared with the experimental results. The analysis of the external pressure is less than 30 GPa CeO_2, the mechanical and dynamic stability, CaF2 structure, elastic modulus, hardness, toughness and anisotropy changes with pressure. The introduction of Hubbard U parameter correction effect of strong correlation of the Ce4f electrons, CeO_2 analysis of density of States and charge distribution, Ce ion and O ion distribution of electronic states and bonding the change of understanding pressure, in-depth understanding of mechanical properties of.2, effect of fluoride on the properties of mechanical and electronic structure of CeO_2. The effects of fluorine doped three possible positions always, calculation of dopant formation, determine the steady structure of fluorine modified CeO_2. Six kinds of fluorine doped amount of CeO_ (2-x) elastic mechanical properties of F_x, elastic analysis modulus, hardness, toughness and anisotropy changes with fluorine content, determination of fluorine content to maintain mechanical polishing performance. Calculation of four fluorine doped CeO_ (2-x) F_x density of States and charge distribution, analysis of F ion and Ce ion, O points The interaction of density, and elucidate the mechanism of fluorine atom doping effect on CeO_2 elastic mechanical properties. Changes of.3 to investigate the elastic mechanical properties and electronic structure of the CeC1.75F0.25 system in polishing under pressure, CeO_2 fluoride and the influence on the crystal morphology and relaxation. Construction calculation of CeO_2 (111) surface, CeO_2 (100) and (110) surface energy, three kinds of surface energy, and calculated with other literature values compared with the experimental value. To calculate the adsorption potential F single atom in the three surface, determining the stable adsorption configuration, adsorption of F atoms on the surface of the surface of three, forecast the final shape of polishing powder grain. Research on different F atomic coverage (111) and (100) the surface energy difference effect on crystal morphology. The calculation of surface and sub surface oxygen vacancy formation energy of F atoms from the (100) surface to surface oxygen vacancies, and a Step into the subsurface migration of oxygen vacancies can activate, determine the F atoms from the surface to the inner diffusion control factors. Research on CeO1.75F0.25 system (111) and (100) surface electronic structure, determination of fluoride on the surface of the Ce-O bond,.4 always and the surface energy of the polishing reaction process of cerium based polishing powder fluoride the construction of CeO_2 (111) and CeO1.75F0.20 (100) two kinds of grinding surface, calculation of SiO_2 grains in the adsorption of two kinds of surface energy, determine the stability of the initial configuration. The reaction process was a detailed study of two kinds of surface grinding grain SiO_2, analysis of Si atom, the evolution of bond breaking, fluorine in judgment the chemical polishing process.

【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG739

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