【作者】 周永山；

【导师】 林彦军；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2012， 硕士

【摘要】 纳米颗粒在制备过程中极易产生自发的团聚，进而生成粒径较大的二次团聚体，导致纳米颗粒材料的性能严重劣化，影响了其应用效果。目前针对纳米稀土氧化物的研究大部分仅限于对其一次粒径进行表征，未对其团聚现象进行研究和控制，限制了纳米稀土氧化物的应用范围。本论文针对纳米稀土氧化物在制备过程中发生的团聚现象，采用成核/晶核隔离法将稀土氢氧化物前驱体的成核和晶化过程进行分离，研究了稀土氧化物在制备不同阶段的晶粒生长特点，发现稀土氢氧化物前驱体的成核过程十分迅速，在短时间内得到了大量纳米晶核，但新生的晶粒极易发生团聚生长，导致其二次粒径处于微米级，进而影响了焙烧得到的稀土氧化物的二次粒径分布。本文针对这一现象开展研究，采用可大规模工业化应用的成核/晶化隔离法制备稀土氧化物纳米材料，并引入经表面修饰的碳黑作为硬模板剂抑制制备过程中晶粒之间的二次团聚，实现均分散纳米稀土氧化物的可控制备。本论文针对稀土元素电负性的不同，分别采用浓硝酸和浓硝酸/浓硫酸/过硫酸铵作为改性剂对碳黑进行表面修饰，得到了表面具有-COOH、-SO₄等不同电荷密度基团的改性碳黑模板剂。将La³⁺、Ce³⁺和Y³⁺等金属盐溶液与具有不同表面基团的碳黑模板剂进行混合，加入沉淀剂得到稀土氢氧化物前驱体，经焙烧后得到了均分散纳米稀土氧化物微晶。研究发现：1.由于La³⁺、Ce³⁺和Y³⁺能够与改性碳黑表面带负电荷的基团发生静电吸附，在碳黑表面均匀成核得到了均分散稀土氢氧化物前驱体；2.由于La和Ce具有较小电负性，对氢氧根的作用较弱，其氢氧化物易发生电离作用而使表面带正电荷，并产生较高的表面正电位，能够与-COO－等具有较低电荷密度的基团发生静电吸附作用，从而避免了氢氧化物晶核在生长过程中的团聚现象；3. Y元素具有较大电负性，对氢氧根的作用较强，其氢氧化物不易发生电离作用而使表面带正电荷较少，表面电位较低，需与-SO₄^2-等具有较高电荷密度的基团发生静电吸附作用，从而避免氢氧化物晶核在生长过程中的团聚现象；4.在焙烧过程中，由于碳黑模板剂能够释放出大量CO₂，可以有效抑制稀土氢氧化物分解过程中的颗粒团聚，从而得到了无明显团聚现象、二次粒径与一次粒径相当的均分散纳米稀土氧化物，并表现出了较好的荧光性能。本文还开展了采用碳黑为模板剂制备Eu和Tb掺杂的系列均分散稀土氧化物的研究，结果表明得到的系列掺杂纳米稀土氧化物晶粒大小均匀且无明显团聚现象，其荧光效率与不采用模板剂相比显著提高。更多还原

【Abstract】 Nanoparticles are susceptible to make a reunion of spontaneous, and thengenerate the reunion body with large second particle size, leading to the loss ofexcellent materials properties and application effect. At present, the study ofnanometer rare earth oxides mostly confined to the primary particle size,however, the research and control of the aggregation phenomenon whichlimited the scope of application of nano rare earth oxide causes little attention.This paper focused on the reunion phenomenon of the industrialproduction of rare earth oxides. We intensively studied the growthcharacteristics of the rare earth oxides particle during the different preparationstage using the method involving separate nucleation and aging steps. Then wediscover the nucleation process and the growth of crystal nucleus in thefollowing part are both very fast which leading the second particle size at themicrometer level, thereby affecting the two particle size distribution of rareearth oxide. In view of this phenomenon, we prepared the controllable uniformdispersion nano rare earth oxide by using the large-scale industrial method involving separate nucleation and aging steps, and introducing the surfacemodified carbon black as a hard template agent which can inhibit the reunionof grains in the preparation process.In this paper, we obtained the modified carbon black template withdifferent charge density group-COOH,-SO4on surface using the concentratednitric acid, sulfuric acid and ammonium persulfate as modifier according tothe difference electronegativity for rare earth element. The metal salt solutionsof La3+, Ce3+and Y3+are mixed with different surface groups of carbontemplate agent, adding a precipitating agent to obtain the rare earth hydroxideprecursor, then the uniformly dispersed nano rare earth oxide microcrystals isprepared after roasting. Study finds:1. The rare earth hydroxide precursor is prepared by the homogeneousnucleation on the surface of modified carbon black, because of theelectrostatic adsorption between the La3+, Ce3+and Y3+and the negativelycharged groups on carbon black surface.2. Compared with Y, La and Ce are less electronegative, and the control forhydroxyl is weak, so their hydroxides are prone to ionize and the surfacesare positively charged with higher surface positive potential, then absorbedthe-COO–and the other low charge density groups for modified carbonblack, thus avoiding the reunion phenomenon of hydroxide crystal innucleus growing process.3. The control effect for hydroxyl is stronger because of Y element with a higher electronegativity, and the hydroxide is not easy to ionize and thesurface potential is lower, so the higher charge density-SO₄（2-）is needed forthe lectrostatic adsorption, thereby avoiding the agglomeration ofhydroxide crystal nucleus in the growing process.4. The template can effectively inhibit the agglomeration of particles of therare earth hydroxides in the decomposition process because the carbonblack can release a large amount of CO2during the baking process. So weobtained monodispersed nanometer rare earth oxides with equivalentparticle diameter and second particle size which showed good fluorescenceproperties.We also carried out the research using carbon black as template inpreparation of Eu and Tb doped series dispersed rare earth oxides in this paper.The results showed that the range of grain size distribution for doped nano rareearth oxide was uniform and no agglomeration, and the fluorescent efficiencywas significantly improved comparing with those with no template agent.更多还原