【作者】 王绍艳；

【导师】 翟玉春；

【作者基本信息】 东北大学 ， 冶金物理化学， 2009， 博士

【摘要】 本课题采纳液相直接沉淀法以建立简单、成本低、效率高、易于工业化生产、无污染、产品无团聚的制备纳米金属氧化物的工艺。在传统的沉淀法制备纳米金属氧化物中,通常采用水为反应介质或以水为主要反应介质,硬团聚的产生是不可避免的。为此,本课题利用沉淀表面吸附的铵盐的静电作用、隔离作用和热解气体对沉淀起到的一定阻隔作用克服团聚。实验以ZrOCl₂水溶液为滴定液、NH₃·H₂O水溶液为被滴定液,在室温下进行沉淀反应,所获沉淀不经水洗,直接干燥和焙烧,获得分散纳米ZrO₂。从干燥开始到焙烧400℃左右,沉淀表面吸附的NH₄Cl一直存在,对产品起到分散作用,500℃时NH₄Cl完全分解,不影响产品纯度,产品为四方相;超过600℃时,产品为单斜和四方相共存,产品平均粒度在13-35nm之间。沉淀经水洗,产品则团聚。使用合适用量的表面活性剂聚乙二醇使沉淀反应溶液的表面张力和粘度都接近最低值,和NH₄Cl共同作用,能进一步提高产品的分散性。因为沉淀颗粒表面的吸附水所形成的氢键是硬团聚产生的根源,所以本课题用乙醇取代水作反应介质来降低硬团聚产生的可能性。把反应物均配成乙醇溶液,即可使沉淀反应在乙醇介质中进行,使沉淀从一开始形成时就避免因大量水分子的带来的团聚问题。本实验以氯氧化锆和氨水为原料,乙醇为介质,进行沉淀反应得到ZrO（OH）₂胶体,经过滤、乙醇洗涤、干燥、焙烧等过程制备均匀分散的纳米ZrO₂。用均匀设计法考察了反应物摩尔比、乙醇含量、氯氧化锆浓度、反应温度、表面活性剂五因素对产品粒径、分散性和产率的影响,结果表明:乙醇含量是主要影响因素,其用量增大,有利于获得粒径小、分散性好、产率高的纳米ZrO₂。实验过程中使用的乙醇,包括沉淀反应母液和用作洗涤液的乙醇,都可经过蒸馏回收并可循环使用,同时得到NH₄Cl。本工艺过程属于绿色化学过程。为了控制经高温焙烧后粉体粒径的长大,可采取先将胶体低温焙烧,用盐酸浸泡处理再高温焙烧的方法或分阶段热处理的方法。本实验以ZrOCl₂·8H₂O为原料,Y（NO₃）₃·6H₂O、MgCl₂·6H₂O、AlCl₃·6H₂O、Ca（NO₃）₂·4H₂O分别为掺杂剂,NH₃·H₂O为沉淀剂,采用乙醇沉淀法制备Y₂O₃-ZrO₂、MgO-ZrO₂、Al₂O₃-ZrO₂、CaO-ZrO₂陶瓷粉体。用干压成型法在一定的压力下压制素坯后进行烧结。考察了反应介质、焙烧温度对粉体粒径、分散性的影响以及粉体性质、掺杂剂加入量、成型压力等因素对素坯及烧结体密度的影响。结果表明:乙醇为反应介质制备的ZrO₂陶瓷粉体粒径均小于30nm,尺寸分布范围窄,分散性好,粉体烧结活性高,zrO₂主要以四方晶型存在,并含有少量单斜相。由这些陶瓷粉体制得的烧结体断裂面平整,且无裂缝。Y₂O₃-ZrO₂、MgO-ZrO₂、Al₂O₃-ZrO₂、CaO-ZrO₂陶瓷烧结体的最佳成型压力分别为10MPa、7MPa、20MPa、20MPa。3%（mol）Y₂O₃、5%（mol）MgO、20-60%（mol）Al、5-20%（mol）CaO的ZrO₂陶瓷素坯相对密度均在50%左右,3%（mol）Y₂O₃、10%（mol）MgO、20-80%（mol）Al、5-15%（mol）CaO的ZrO₂陶瓷烧结体相对密度均在95%以上,接近理论值。本实验以三氯化铝为原料,氨水为沉淀剂,乙醇为介质,在室温条件下进行液相沉淀反应,得到Al（OH）₃胶体,经过乙醇洗涤、干燥、焙烧等过程了均分散的纳米γ-Al₂O₃。考察了三氯化铝的浓度、三氯化铝与氨水的摩尔比、焙烧温度对产率和比表面积的影响,结果表明:前两者决定产品的产率,后者决定产品的粒度、晶型、比表面积。焙烧温度为686-1029℃时,获得均匀分散的γ-Al₂O₃纳米粉,粒径5-9nm,比表面积为204-102 m²/g。采用乙醇为介质的直接沉淀法还可应用于其他纳米氧化物如氧化镁、氧化锡、氧化钛的制备。论文中利用热重—差热分析（TG-DTA）和红外光谱（IR）分析前驱体的热处理过程;用透射电子显微镜（TEM）观察粉体的形貌、大小及其分布;用X射线衍射光谱（XRD）检测粉体的相组成;用扫描电子显微镜（SEM）研究烧结体的显微结构。更多还原

【Abstract】 This paper adopted direct liquid phase precipitation in order to establish a facile technique to prepare dispersed metal oxides and this technique has the advantages of simple operation, low cost,high efficiency,no pollution and free-agglomeration of the product and is easy to be industrialized.In terms of the traditional precipitation to prepare nano metal oxide,water was usually used as a reaction medium or major medium,unavoidable hard agglomeration occurred.Our research overcame this agglomeration phenomenon by separating function and electrostatic interaction caused by ammonium salt absorbed on the precipitate surface,and isolation of pyrolytic gas to the precipitate.With ZrOCl₂ aqueous solution as the titrant and NH₃·H₂O aqueous solution as the titrate,nano ZrO₂ powder was prepared via precipitation at room temperature followed by a drying-calcining treatment.From the beginning of the drying process up to the calcining process of 400℃,NH₄Cl was absorbed on the precipitate surface and played a role of dispersive action.When at 500℃,NH₄Cl was fully decomposed and had no influence on product purity and the product existed in tetragonal form.Calcined over 600℃,the products coexisted in monoclinic and tetragonal forms and their average sizes were between 13-35 nm.If the precipitate was washed with water,the product agglomerated. Adding suitable amount of surface active agent PEG made the values of surface tension and viscosity of the precipitation solution access to the lowest and the product dispersity was improved via the synergism of NH₄Cl and PEG.Because the hydrogen bond formed via absorbed water on the precipitate surface is the origin to cause hard agglomeration,alcohol was used as reaction medium instead of water to reduce this possibility in this research.Dissolving the reactants in alcohol,we avoided the agglomeration caused by the great amount of water from the beginning of the formation of the precipitate.By using ZrOCl₂ and NH₃·H₂O as raw materials,nano ZrO₂ was prepared via a series processes of ZrO（OH）₂ gel precipitated in ethanol,filtrated,washed with alcohol,dried and calcined.The influences of five experimental parameters upon the mean size,dispersity and yield of the product were investigated via uniform design.These parameters were molar ratio of NH₃·H₂O to ZrOCl₂,C₂H₅OH percentage in reacting and washing solutions,ZrOCl₂ concentration,precipitation temperature and surfactant PEG-800 dosage.The condition experiments demonstrated that the C₂H₅OH percentage was the major factor and the higher the C₂H₅OH percentage,the smaller the size,the better the dispersity and the higher the yield of the product.In the precipitation and washing process,the mother liquor and the filtrate could be distilled to recycle ethanol and gain byproduct NH₄Cl simultaneously.This was a simple green process.In order to prohibit the powder size from getting larger after calcinated at high temperature,we applied the approach in which the gel was calcinated at low temperature beforehand,marinated in HCl（aq）,then calcinated at high temperature again or the other method of grading heat treatment.This kind of alcohol precipitation was adopted to prepare Y₂O₃-ZrO₂,MgO-ZrO₂, Al₂O₃-ZrO₂ and CaO-ZrO₂ composite ceramic powder by using ZrOCl₂·8H₂O as the raw material,Y（NO₃）₃·6H₂O,MgCl₂·6H₂O,AlCl₃·6H₂O,and Ca（NO₃）₂·4H₂O as the dopant respectively,and NH₃·H₂O as the precipitant.The green compacts were formed by dry pressing under certain pressure and then sintered.The effects of the reaction media and calcining temperature on the size and dispersity of the powders as well as the property of the powders,the dosage of the dopant and the compacting pressure on the density of the green compacts and sintered bodies were studied.,The experiment findings showed that when ethanol was used as the reaction medium the sizes of the nano-zirconia composite powders were less than 30 nm and the powders had the narrow size distribution,good dispersity and high sintering activity.The form of ZrO₂ was major tetragonal with minor monoclinic.The fractured surfaces of the sintered bodies prepared by the composite ceramic powders were smooth without any cracks.The optimal pressure for Y₂O₃-ZrO₂,MgO-ZrO₂,Al₂O₃-ZrO₂ and CaO-ZrO₂ sintered bodies were 10MPa,7MPa,20MPa and 20MPa,respectively.The relative densities of the ZrO₂ green compacts respectively doped with 3%（mol）Y₂O₃,5%（mol）MgO, 20～60%（mol）Al and 5～20%（mol）CaO were about 50%.The relative densities of the ZrO₂ sintered bodies respectively doped with 3%（mol）Y₂O₃,10%（mol）MgO,20～80%（mol）Al and 5～15%（mol）CaO exceeded 95%and were close to the theoretical value.Nanosizedγ-alumina powder was prepared via precipitation of AlCl₃ and NH₃·H₂O ethanol solution followed by the process of alcohol washing,drying treatment and calcination.The effects of the reactant concentration,the molar ratio of reactants and the calcination temperature upon the yield and the specific surface area of the product were explored.The experimental results showed that the former two factors determined the product yield and the latter determined the size,phase and specific surface area of the product etc.When the calcination temperatures were controlled between 686-1029℃,the highly dispersed nano-sizedγ-alumina particles with a size range of 5-9 nm and specific surface area of 204-102m²/g were obtained.The direct precipitation process in which ethanol was used as the medium could be applied to synthesize other nano oxides such as magnesium oxide,stannic oxide,aluminum oxide and some stable ZrO₂ ceramic powder.In this paper,the heat treatment process of the precursors was analyzed by thermogravimetry differential thermal analysis（TG-DTA） and infrared spectrum（IR）,the morphology,the size and distribution of the particles were observed by transmission electron microscopy（TEM）,the phase composition of the powders was detected by X-ray diffraction （XRD）,the microstructure of sintered bodies was studied by scanning electron microscopy （SEM）.更多还原