溶胶-凝胶法制备纳米稀土镧掺杂钼粉

采用液-液掺杂方式将仲铝酸铵、硝酸镧以及柠檬酸溶液混合,采用溶胶-凝胶法制备纳米稀土镧掺杂钼粉.研究初始溶液pH值和柠檬酸添加量对成胶效果的影响,讨论干凝胶的除胶工艺,分析稀土镧在掺杂铅粉中的存在形式.结果表明:当初始溶液的pH值为1且柠檬酸的添加量为仲钼酸铵质量的1.5倍时,可制备出疏松多孔、网状结构、成胶效果良好的干凝胶.采用直接烧结法在560℃焙烧可将胶体很好地除去,两段还原后得到颗粒为球形且十分均匀的纳米掺杂Mo粉.在掺杂MoO3粉中,镧以La2O3或La-Mo复合氧化物形式存在,稀土颗粒粘附在MoO3颗粒表面.在MoO3的还原过程中La-Mo复合氧化物分解,镧以La2O3的形式存在于Mo粉中.钼粉颗粒尺寸在500 nm左右,掺杂La2O3的尺寸约100nm.     

纳米氧化镧及其复合氧化物的制备及应用最新研究进展

纳米氧化镧及其复合氧化物不同于常规微米氧化镧及其复合氧化物,既显示出纳米材料所具有的独特性能,如界面效应、小尺寸效应、宏观量子隧道效应等,又表现出比表面积大、催化活性高、吸附选择性强、晶格氧迁移等优良特性。近年来,纳米氧化镧及其复合氧化物应用范围随其新颖特性的发现而不断拓展,同时也吸引了国内外很多学者对其开展了大量的研究工作,对常用的传统制备方法(如固相法、水热法、沉淀法、溶胶凝胶法)不断进行改进,并提出如静电纺丝法和反相乳液法等多种新型制备方法来解决因制备方法本身的局限性而造成的纳米粒子间容易发生团聚、粒度分布不均等问题。综述了静电纺丝法、反相乳液法和熔盐法等制备方法的最新研究情况,也深入介绍了纳米氧化镧及其复合氧化物在光催化材料、传感器材料、电池电极材料、发光材料等应用领域的国内外最新研究进展。     

低温燃烧法合成掺钙铬酸镧粉体的工艺优化

通过正交试验,确定了用柠檬酸-硝酸盐体系制备有机前驱体,低温燃烧法合成掺钙铬酸镧粉体的优化工艺参数,讨论了粉体煅烧温度、柠檬酸量、溶胶pH值、乙二醇量、溶胶陈化时间和掺钙量对粉体BET比表面积的影响.结果表明,影响粉体BET比表面积的因素主次顺序为煅烧温度、柠檬酸量、pH值、乙二醇量、陈化时间、掺钙量.采用优化工艺制备粉体的BET比表面积为18.2m2/g.     

溶胶-凝胶法制备稀土CeO2掺杂纳米钨粉的研究

以偏钨酸铵(AMT)、柠檬酸和硝酸铈为原料,用溶胶-凝胶法(sol-gel)制备稀土CeO2掺杂纳米钨粉。通过热重-差热(TG-DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、比表面积法(BET)等测试手段对复合粉体的合成工艺、物相、颗粒形貌和粒径进行了分析。结果表明:当pH值为1时,还原后的粉体颗粒呈准球形,无团聚,稀土元素以CeO2形式存在且均匀地分布在钨粉中,平均颗粒粒径为80nm左右,满足制备高性能掺杂稀土氧化物亚微米结构浸渍阴极的要求。     

制备方法对( Ce0.6Zr0.4O2)0.5(Al2O3)0.5储氧材料性能的影响

分别利用氨水共沉淀法和柠檬酸溶胶-凝胶法制备稀土储氧材料( Ce0.6Zr0.4 O2)0.5(Al2 O3)0.5,并用XRD、BET、H2 - TPR、SEM和EDX等手段研究制备方法对(Ce0.6 Zr0.4 O2 )0.5( Al2O3 )0.5的晶相结构、比表面积、平均孔径、孔容、储氧性能、还原性能、样品各组分含量以及颗粒形貌的影响.结果表明两种方法制备样品均为立方晶相的CeO2 - ZrO2 - Al2 O3固溶体,无Al2O3的晶相.但与氨水共沉淀法比较,柠檬酸溶胶-凝胶法制备样品的比表面积、孔容较大,储氧性、还原性和热稳定性能较高.SEM和EDX测试结果表明,氨水共沉淀法制备样品有明显的聚集现象,而柠檬酸溶胶-凝胶法制备样品的颗粒粒径小,分布均匀,且原子组成更接近理论值.     

镧锶钴复合氧化物的水热合成与表征

以硝酸镧、硝酸锶、硝酸钴为金属源,柠檬酸为络合剂,采用水热法于180℃下保温24 h合成镧锶钴复合氧化物.XRD分析表明产物为斜方六面体钙钛矿结构的La0.8Sr0.2CoO3-δ晶相.SEM分析表明产物为球状颗粒,尺寸约0.5～1μm.红外吸收光谱表明产物主要为La0.8Sr0.2CoO3-δ,此外还残留部分柠檬酸和...     

凝胶-微乳液化学剪裁制备Ni-Fe复合纳米微粒(Ⅱ) 相关参数对微粒的组成及粒径分布和磁性的影响

用XRD，TEM，EDS及振动磁强计研究了凝胶-微乳液化学剪裁技术制备明胶包裹的复合纳米量级铁镍超细微粒时。微乳液的水池半径R和Ni／Fe比等参数对微粒的组成及粒径分布和磁性的影响。结果表明：微粒为明胶包裹球形超细微粒。微球的平均粒径为48--136nm，单个微粒的粒径2．3—3．4nm。每个复合微球中约有21～40个铁-镍粒子，微粒有优良的磁性。高的矫顽力。X射线衍射和X射线能谱分析表明有Ni-Fe合金相形成。     

共沉淀-喷雾干燥法合成高比表面积锰酸镧锶的研究

采用共沉淀-喷雾干燥组合技术合成了高比表面积的钙钛矿型锰酸镧锶复合氧化物催化剂粉体材料,对粉体材料进行了XRD、SEM、BET和粒度等表征,700℃煅烧4h,催化剂粉体比表面积达到54.45m2/g,对CO的起燃温度T10=53.5℃,完全燃烧温度T90=136.6℃,显示出很好的催化活性.     

固体超强酸S_2O_8~(2-)/TiO_2-WO_3的制备及其催化性能研究

用溶胶-凝胶法制备了固体超强酸S2O82-/TiO2-WO3,并对其进行了XRD与IR表征,用乙酸乙酯合成模型反应考察了其催化性能,系统研究了WO3的含量、焙烧温度等制备条件对S2O82-/TiO2-WO3性能的影响。实验表明:在(NH4)10W12O41.xH2O质量分数为5.0%、焙烧温度为500℃条件下通过溶胶-凝胶法制备的固体超强酸S2O82-/TiO2-WO3,其载体为微细且晶格不太完整的锐钛矿型TiO2,比表面积较大,具有比浸渍法制备的SO42-/TiO2更高的硫含量和更强酸性,并具有较高的催化酯化活性和稳定性,在反应条件为:醇酸摩尔比1.48∶1、催化剂用量为冰醋酸的6.0%、反应时间2.0h,乙酸转化率可达74.1%(不加分水器)。催化剂在无需任何再生的条件下重复使用,活性下降趋势平缓,显示良好的稳定性。     

溶胶-凝胶法在纳米La1-xMxCrO3粉料制备中的应用

掺杂二价碱土金属的铬酸镧是目前研究最深入和应用效果最好的固体氧化物燃料电池(SOFC)的连接材料,它几乎占整个SOFC制造成本的一半。制备工艺有固相法、溶胶-凝胶法、化学共沉淀法、联氨法和水热法等。本文综述了溶胶-凝胶法及用该方法制备La1-xMxCrO3(M=Sr,Ca)材料的现状。     

Preparation of Ca Doped Lanthanum Chromite by Sol-Gel Process

Super fine particles of calcium-doped lanthanum chromites were prepared by the sol-gel process in which the chelating agent was citric acid and the dispersant agent was ethylene glycol. The phase of fine particles was analyzed by XRD and the size and shape of the particles were investigated by TEM. The result shows that the nano-particles of La1-xCaxCrO3 can be obtained by the way of Ca2 complex singly with citric acid and being calcined at 700 ℃.     

Preparation of La0.9RE0.1MnO3 Ultra-fine Particles Used for CH4 Oxidation

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柠檬酸络合法微波烧结制备复合氧化物La1-xPbxMnO3

采用柠檬酸络合法微波烧结制备了钙钛矿型复合氧化物La1-xPbxMnO3(x=0.2、0.3、0.5、0.6、0.8)载体,并用XRD、SEM及BET对制备的载体进行了表征.实验结果表明微波烧结15min时可得到结晶性较好的单相钙钛矿型复合氧化物,且载体的孔径分布较好,空隙率较大.用沉淀法将活性组分Pd负载于载体上制得的非均相催化剂进行碳酸二苯酯(DPC)合成实验,结果表明所制催化剂活性较好,产品DPC的收率在7%左右.     

工艺条件对硝酸银溶液雾化热分解制备超细银粉的影响

以AgNO₃溶液为原料、柠檬酸为添加剂,在空气气氛下采用溶液雾化热分解法制备超细银粉.采用扫描电镜、激光粒度仪、振实密度测试仪、X射线衍射仪等对银粉进行了表征,系统地研究了反应温度、硝酸银溶液浓度、硝酸银溶液pH值、压缩空气流量、柠檬酸用量等工艺条件对产物银粉形貌、振实密度和平均粒径的影响.结果表明:在反应温度为700 ℃、硝酸银溶液浓度为2.0 mol/L、柠檬酸的添加量为2.5 %（摩尔比）、压缩空气流量为1.0 m3/h、硝酸银溶液pH值为6.0的条件下,可制备得到物相单一、表面光滑、分散性好的球形银粉,银粉的振实密度为4.24 g/cm3,平均粒径为3.16 μm.      

Effects of Synthetic Parameters in Pechini Method on the Formation and Properties of （ZrO2） 0. 92 （ Sc2O3 ） 0.08 Solid Solution

Homogeneous (ZrO2)0.92 (Sc2O3)0.08 solid solution in fluorite cubic structure was prepared from the gels with altered molar ratios of citric acid (CA) to metal ions (M) and ethylene glycol (EG) via a polymerization route (Pechini method). Due to the enhanced chemical homogeneity (high level of mixing of metal ions and ligands) in the polymeric gels, Sc-doped zirconia can be crystallized at temperatures as low as 400 ~C. During the evolution from amorphous gel to the crystallized (ZRO2)0.92 (Sc203)0.08 fine powder, the bonding nature between carboxylate groups and Zr/Sc cations changed: unidentate→bridging→ionic upon calcination. The molar ratios of CA/M (1～4) and CA/EG (0.2～4) were demonstrated to affect the thermal behavior of the gels and thus the particle properties of the derived nanoparticulate oxide powders (including particle size and surface area). The as-sintered sample compacted from the nanosized powders prepared by calcining the gel with the highest content of organics (CA/M =4and CA/EG=0.2) exhibited the best sinterability and the highest oxide ion conductivity.     

Effect of Complex Agents on Structure and Activity of Fe-Substituted Rare Earth Hexaaluminate Catalysts for Methane Combustion

A series of catalysts were prepared by using complex sol-gel methods.Experimental results confirm the effect of different agents on structure and activity of Fe-substituted rare earth hexaaluminate catalyst (LaFeAl11 O19 ) for methane combustion.The catalyst is yielded by complex sol-gel, respectively using three different complex agents (maltose, glucose and citric acid).XRD demonstrated that haxaaluminate is the major phase of catalyst prepared by maltose,while LaAlO3 is the major one of the catalyst by glucose and citric acid.At the same time, there is a little LaFeO3 and surface areas as well as 29.5 nm particle diameter when the complex agent is maltose.However, T10 ( temperature for 10% conversion of methane) and T100 ( temperature for 100% conversion of methane) for catalyst by glucose is 543 and 758 ℃, which is the best among the three complex agents for methane combustion.     

Citric Gel Synthesis and Luminescent Properties of Ce^3＋-Activated SrGa2O4 Phosphor

Ce^3＋-activated SrGa2O4 phosphor was synthesized by a method of citric gel,wherein citric acid served as a chelate agent,and the as-synthesized powder was calcined in a slightly reduced ambient.The crystallization characteristics of the sample varied with the calcining temperature.Compared with the phosphor prepared by the solid-state reaction,the phosphor synthesized by citric gel was calcined at a relatively lower temperature.Consequently,the volatilization of Ga2O3 during high-temperature calcining process was avoided.The typical double-peak emission of Ce^3＋ originated from 2D（5d）→4F5/2（4f）,and 2D（5d）→4F7/2（4f）was observed,and the intrinsic emission of SrGa2O4 host was much restricted.The emission intensity varied with the calcining temperature because the different crystallinity and the optimal concentration of Ce-dopant was determined at 3%.     

MoO2氢还原机理探索

在MoO2还原为钼粉的过程中,大颗粒钼粉(指筛上物)的杂质含量会远远高于小颗粒钼粉。本文采用"核收缩"的理论模型来解释了这一现象。在MoO2氢还原为Mo的过程中,产生一种比起钼的其他化合物挥发性更强的氧化钼的水合物MoO3.H2O或MoO2(OH)2,这种水合物结合从MoO2收缩核中扩散出来的杂质,挥发沉积到长大的Mo颗粒的表面。大颗粒Mo粉的表面积大、表面能低,挥发性水合物更容易沉积在由众多细小颗粒团聚而成的大颗粒表面,从而造成大颗粒钼粉的杂质含量较高。     

稀土镧在La-Mo合金粉中的存在形式及对钼粉性能的影响

通过对添加硝酸镧的二氧化钼在不同温度还原后钼粉的X射线衍射检测分析,研究了稀土镧在La-Mo合金粉中的存在形式;对La-Mo合金粉的粒度、氧含量、SEM照片等结果与纯钼粉对比分析,研究了稀土镧对La-Mo合金粉性能的影响。结果表明:随着还原的进行,稀土镧由以La2O3和钼酸镧的形式存在,逐渐转化为以唯一的La2O3形式存在;稀土镧强烈地抑制了钼粉颗粒的长大;由于稀土镧的加入,钼粉氧含量增加;La-Mo合金粉形貌为规则的多面体,分布不均匀。     

Combustion Synthesis, Character and Electromagnetic Properties of Nano-Sized La0.8Sr0.2FeO3 Perovskite

The perovskite-type nanocrystal La0.8Sr0.2FeO3 was prepared using a sol-gel auto-combustion method with citric acid as the chelating agent. The metal ions coordination compound, obtained from nitrate and citrate, underwent an autocombustion process and voluminous ashes formed when calcining the complex in the air. Some analytical methods, which consisted of FT-IR, XRD, TEM and wave-guide, were used to characterize the gel and the final products. It was shown that metal ions and carboxyl were combined to form a homogeneous organic complex base salts in the process of gelation. The nanocrystalline had dielectric loss in the microwave frequency range of measurement.