本文選題：氟化　切入點：二氧化鈰　出處：《北京化工大學》2017年博士論文　論文類型：學位論文

【摘要】：稀土作為戰(zhàn)略性資源重要性堪比石油,內(nèi)蒙古包頭市具有全球最大的白云鄂博輕稀土礦,該礦中約含50%的鈰。作為鈰元素的原料和加工基地,包頭近年來出現(xiàn)了多家鈰基稀土拋光粉企業(yè),開辟了一個輕稀土新材料應(yīng)用領(lǐng)域。由于CeO_2表面活性高、極易團聚、顆粒形貌不規(guī)則,不能直接用于精密拋光。目前市售鈰基拋光粉大多進行氟化處理,該工藝是向氧化鈰前驅(qū)體中加入氟化劑,如氫氟酸、氟硅酸、氟化銨或氟化鈉等進行氟化反應(yīng)。實驗表明,氟化鈰基拋光粉的顆粒形貌由棒狀或片狀等變?yōu)?類)球形,團聚顯著地減弱,提高了被拋光件表面光潔度。為研究鈰基稀土拋光粉中氟行為的作用機理,本文采用第一性原理方法,研究了氟化氧化鈰體相和表面的穩(wěn)態(tài)結(jié)構(gòu),氟化氧化鈰晶體對機械拋光性能的影響,氟對氧化鈰拋光粉晶體形貌的影響,氧化鈰氟化過程的控制因素。氟原子在化學拋光氧化硅玻璃中的作用。從電子結(jié)構(gòu)角度分析了氟化對體相的宏觀力學性能和表面的表面能影響的內(nèi)在原因。給出鈰基復合拋光粉的最佳氟含量,為開發(fā)高端鈰基拋光粉提供理論依據(jù)。主要工作如下:1、常壓及外壓下CeO_2力學性能和電子結(jié)構(gòu)分析。通過計算結(jié)合能與彈性常數(shù),判斷常壓下CeO_2力學穩(wěn)定性;計算CeO_2的體積模量、剪切模量、楊氏模量、維氏硬度,并與實驗結(jié)果進行比較。分析外壓低于30 GPa時,CaF2結(jié)構(gòu)的CeO_2力學和動力學穩(wěn)定性,彈性模量、硬度、韌性和各向異性隨壓力的變化。引入Hubbard U參量修正Ce4f層電子的強關(guān)聯(lián)效應(yīng),分析CeO_2態(tài)密度和電荷密度分布,了解外壓下Ce離子和O離子電子態(tài)分布及成鍵的變化,深入理解力學性能改變原因。2、氟化對CeO_2力學性能和電子結(jié)構(gòu)影響。考察氟摻雜三種可能位置的總能,計算摻雜形成能,確定氟改性CeO_2的穩(wěn)態(tài)結(jié)構(gòu)。研究六種氟摻雜量時CeO_(2-x)F_x的彈性力學性能,分析彈性模量、硬度、韌性和各向異性隨氟含量的變化,確定保持機械拋光性能的氟含量。計算四種氟摻雜體系CeO_(2-x)F_x的態(tài)密度和電荷密度分布,分析了 F離子與Ce、O離子分波態(tài)密度的相互作用,闡明氟原子及其摻雜量對CeO_2彈性力學性能的影響機理。研究了 CeC1.75F0.25體系的彈性力學性能和電子結(jié)構(gòu)在拋光外壓力下的變化。3、CeO_2的氟化及對晶體形貌影響。構(gòu)建并弛豫計算CeO_2(111)表面、CeO_2(100)和(110)重構(gòu)表面的總能,比較三種表面的表面能,并與其他文獻的計算值和實驗值相比較。計算F單原子在三種表面的吸附勢能面,確定穩(wěn)定吸附構(gòu)型,比較吸附F原子后三種表面的表面能,預(yù)測了拋光粉晶粒的最終形貌。研究不同F(xiàn)原子覆蓋度下(111)和(100)面的表面能差對晶體形貌的影響。計算表層及次表層氧空位形成能,研究F原子從(100)表面遷入表層氧空位,并進一步遷入次表層氧空位的遷移激活能,確定F原子從表面向體內(nèi)擴散的控制因素。研究CeO1.75F0.25體系的(111)和(100)表面的電子結(jié)構(gòu),確定氟對表面的Ce-O成鍵、總能和表面能的影響。4、氟化鈰基拋光粉的拋光反應(yīng)過程。構(gòu)建CeO_2(111)和CeO1.75F0.20(100)兩種磨削表面,計算SiO_2晶粒在兩種表面的吸附能,確定穩(wěn)定的初態(tài)始構(gòu)型。詳細研究兩種表面磨削SiO_2晶粒的反應(yīng)過程,分析Si原子成鍵、斷鍵的演變情況,判斷氟元素在化學拋光中的作用。
[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.

【學位授予單位】：北京化工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG739

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