AACH热分解法制备α-Al2O3超细粉末

以NH4Al(SO4)2与NH4HCO3为原料,采用共沉淀法制备出前驱物碳酸铝铵(AACH),并煅烧得到超细α-Al2O3粉末. 研究了pH值、滴加速度及醇水混合溶剂等因素对反应产物的影响,并对前驱物AACH的高温相变过程和α-Al2O3籽晶对θ-Al2O3→α-Al2O3相变的影响进行了分析.利用XRD、TEM和BET等对粉体的性能进行表征.结果表明:在醇水混合溶剂中控制反应体系的pH值为9～10,将硫酸铝铵溶液以＜18 mL/min的速度滴入碳酸氢铵溶液,可合成颗粒细小、粒度分布均匀且分散性优异的AACH前驱物.不含籽晶的AACH煅烧时α相完全转化温度为1150 ℃,获得α-Al2O3粒径约为100 nm,而α-Al2O3籽晶的加入可将完全转变温度降至1050 ℃,获得的α-Al2O3粒径约为70 nm.     

氯化铵对AACH热分解制备纳米α-Al2O3的影响

以硫酸铝铵和碳酸氢铵为主要原料,采用沉淀法制备纳米碳酸铝铵(AACH)前驱体,通过碳酸铝铵热分解制备α-Al2O3,并利用X射线衍射(XRD),透射电镜(TEM)对前驱体及其煅烧产物的物相和形貌进行表征.研究表明通过添加氯化铵能够降低α-Al2O3的相变温度,并且随着加入量的增加,颗粒粒径减小,分散性改善.加入10;氯化铵的前驱体在1150 ℃下煅烧1 h后可以得到分散性较好的纳米α-Al2O3颗粒.     

Y_2O_3:Er~(3+)上转换纳米纤维的制备与性质研究

采用静电纺丝技术制备了PVA/[Y(NO_3)_3+Er(NO_3)_3]复合纳米纤维,将其在适当的温度下进行热处理,得到Y_2O_3∶Er~(3+)上转换纳米纤维.XRD分析表明,PVA/[Y(NO_3)_3+Er(NO_3)_3]复合纳米纤维为无定型,Y_2O_3∶Er~(3+)上转换纳米纤维属于体心立方晶系,空间群为Ia3.SEM分析表明,PVA/[Y(NO_3)_3+Er(NO_3)_3]复合纳米纤维的平均直径约为130 nm;经过600 ℃焙烧后,获得了直径约60 nm Y_2O_3∶Er~(3+)上转换纳米纤维.TG-DTA分析表明,当焙烧温度高于600 ℃时,PVA/[Y(NO_3)_3+Er(NO_3)_3]复合纳米纤维中水分、有机物和硝酸盐分解挥发完毕,样品不再失重,总失重率为80;.FT-IR分析表明,PVA/[Y(NO_3)_3+Er(NO_3)_3]复合纳米纤维的红外光谱与纯PVA的红外光谱基本一致,600 ℃时,生成了Y_2O_3∶Er~(3+)上转换纳米纤维.该纤维在980 nm激光激发下发射出中心波长为522 nm、561 nm的绿色和658 nm的红色上转换荧光,对应于 Er~(3+)的~2H_(11/2)/~4S_(3/2)→~4I_(l5/2)跃迁和~4F_(9/2)→~4I_(l5/2)跃迁.对Y_2O_3∶Er~(3+)上转换纳米纤维的形成机理进行了讨论,该技术可以推广用于制备其他稀土氧化物上转换纳米纤维.     

纤锌矿CuInS2纳米晶的合成及其机理研究

采用一步溶剂热法合成纤锌矿结构CuInS2(W-CIS)纳米粉体,并对其生长形成机理进行了研究.利用XRD、FE-SEM及EDS对W-CIS纳米晶的结构和形貌以及元素组成进行分析,研究了溶剂热合成过程中的铜源、硫源、反应温度及反应时间对CuInS2纳米粉体物相及形貌的影响.结果表明:以CuCl2·2H2O或Cu(CH3COO)2·H2O、InCl3·4H2O和硫脲为原料,聚乙二醇400、乙二胺为溶剂于200℃下反应2h可以成功合成出结晶性良好的CuInS2纳米片,直径约为300 nm,厚度大约为10～20 nm.通过研究发现,乙二胺对形成纤锌矿结构CuInS2起着关键的作用,并且该粉体对亚甲基蓝的降解率可达75.04;.     

可磁分离TiO2/BiOI复合纤维的制备及光催化性能

本工作合成了一种可磁分离TiO2/BiOI复合纳米纤维(TiO2/Fe3O4/BiOI),并研究了其可见光催化性能.通过静电纺丝技术获得TiO2纳米纤维,采用溶剂热法在TiO2纳米纤维表面生长Fe3 O4纳米颗粒,最后,在磁场辅助下,通过连续离子吸附反应(SILAR)法在TiO2/Fe3O4表面生长了BiOI纳米片.结果表明,Fe3O4纳米颗粒直径均一,均匀分布在TiO2纳米纤维表面.BiOI纳米片呈交错状垂直沉积在TiO2纳米纤维表面,BiOI纳米片的负载量可以通过SILAR的循环次数控制.光催化测试表明,由于BiOI对可见光吸收的增加,以及与TiO2间形成的半导体异质结,TiO2/Fe3 O4/BiOI复合纳米纤维的光催化效率均高于TiO2/Fe3 O4纳米纤维.此外,TiO2/Fe3 O4/BiOI对外磁场有强的响应,易于进行磁分离回收.     

铝高温氧化过程中表面氧化物的有序转变及形貌观察

采用同步热分析(Simultaneous Thermal Analysis, STA)分析了Al在非高压空气下(压力0.2 MPa,流速20 NmL/min)的氧化过程.用X射线衍射(XRD)对铝粉颗粒表面生成的氧化物进行了物相分析并用扫描电镜(SEM)观察了表面形貌.研究结果表明,140 ℃铝开始氧化,300 ℃以上开始生成γ-Al2O3,一直持续至515 ℃左右.从666.1 ℃开始,表面生成氧化物的铝粉颗粒芯层中的铝熔融.从773 ℃开始,γ-Al2O3转变成α-Al2O3, 800 ℃,α-Al2O3开始生长,α-Al2O3的生长遵循Sigmoid(Boltzmann)模型.整个氧化过程,铝粉的氧化占主要地位,但也包括铝粉的氮化.XRD、SEM的分析结果表明,表面生成的AlN及α-Al2O3为纳米级,弥散分布于铝粉颗粒表面.     

莫来石陶瓷超滤膜的制备与表征

以正硅酸乙脂(TEOS)和Al(NO_3)_3·9H_2O为主要原料,聚乙烯醇(PVA)和甘油为添加剂,通过溶胶-凝胶法和浸渍涂覆法在管状α-Al_2O_3支撑体上制备莫来石陶瓷超滤膜.采用XRD、SEM、N2吸附法、渗透通量和截留分子量测定等方法对制备的超滤膜进行了结构和性能表征.结果表明,莫来石单相溶胶浓度为0.28 mol/L、pH=2.0、PVA和甘油加入量分别为1.5 wt;和6 wt;时,经三次涂覆和1200 ℃保温2 h烧成后,可获得表面结构均匀平整、不开裂的莫来石超滤膜;制备的莫来石超滤膜平均孔径为8.4 nm,厚度约1.8 nm,其平均纯净水渗透通量和聚乙二醇(PEG)截留分子量分别为46.8 L·m~(-2)·h~(-1)·(10~5 Pa)~(-1) 和9 kDa.     

核桃状3D分级结构γ-AlOOH无模板水热合成及对刚果红吸附性能研究

以Al(NO3)3.9H2O为铝源、尿素为沉淀剂,无模板水热法制备了单分散、尺寸均一的核桃状分级结构γ-AlOOH.用XRD、SEM、TEM和氮气吸脱附法对样品进行了表征,探讨了γ-AlOOH纳米结构形成机理,并研究了其对刚果红的吸附性能.实验结果表明,核桃状分级结构组成单元为纳米纤维,比表面积为101.3 m2/g,平均孔径为21.88 nm,并对刚果红表现出良好的吸附特性,吸附率和最大吸附量分别为98.8;和98.8 mg/g.     

碳热原位合成SiC_w/Al_2O_3复相陶瓷粉体的制备工艺及反应机理

本文以高岭土和纳米碳黑颗粒为原料,采用碳热还原原位合成工艺制备SiC_w/Al_2O_3复相陶瓷粉体.通过研究合成温度、保温时间、原料配比以及氩气流量对合成产物的影响,借助XRD、SEM等技术手段进行测试表征,得到了合成工艺的最优参数,并探讨了碳热还原反应的机理.实验结果表明:高岭土与碳黑的摩尔比为1∶ 8,氩气流量为80 mL/min,在1500 ℃下保温2 h,可获得纯净的SiC_w和Al_2O_3复相陶瓷粉体,SiC晶须的平均直径为300 nm左右,长度大于6 μm,长径比大于20,SiC晶须表面光洁,与氧化铝颗粒呈均匀分布.碳热还原高岭土合成SiC_w/Al_2O_3,包括碳热还原SiO_2 与碳热还原莫来石两个阶段,碳化硅晶须的生成遵循气-固(V-S)生长机理.     

碳铵尿素双沉淀法合成球形纳米 α-Al2O3粉体的研究

报道了一种用硝酸铝和碳酸铵以及尿素反应制备球形纳米α-Al2O3粉体的便捷方法.通过X射线粉末衍射、差热分析和扫描电镜对产物进行表征观察,结果显示,用这种方法所合成的前驱体为2～6μm鹅卵石形状的氢氧化铝.前驱体再经1200℃煅烧2 h得到直径为200 nm左右的孪生球形纳米氧化铝粉体.在此过程中,尿素起到了调节形貌的作用.     

滴定方式对纳米NH4AlO(OH)HCO3先驱体制备的影响

本文以NH4Al（SO4）2和NH4HCO3为主要原料,采用均相沉淀法制备纳米NH4AlO（OH）HCO3（AACH）先驱体,利用X射线衍射仪和透射电镜研究了滴定方式对其制备的影响。结果表明：将碳酸氢铵溶液滴入剧烈搅拌的硫酸铝铵溶液中,可获得勃姆石,将硫酸铝铵溶液滴入剧烈搅拌的碳酸氢铵溶液中,则可获得呈纤维状的纳米NH4AlO（OH）HCO3先驱体,分散较好且无明显团聚。     

Influence of solution constituents, solution conditioning and seeding on the crystalline phase of aluminium hydroxide using in situ X-ray diffraction

Filtering, drying and aging of crystalline solids can affect crystalline phase(s) and therefore ex situ X-ray diffraction is not necessarily indicative of the in situ crystalline components. This paper examines some of the factors affecting the crystallised phase of aluminium hydroxides in highly caustic solutions. Caustic aluminate solutions were prepared using several different methodologies. Where solutions were prepared from aluminium metal, gibbsite and bayerite were observed to be the crystallisation products. Where gibbsite was used as the aluminium source in the liquors, the crystallised phase was found to be a function of solution conditioning. Solutions prepared at 100°C and at atmospheric pressure crystallised to form only gibbsite. These same solutions subsequently heated to 160°C for 16 h crystallised as gibbsite and bayerite. It has been concluded from these results that the caustic aluminate solutions made using gibbsite were not dissolved on the molecular scale (although optically clear) if the solutions were heated to only 100°C. Further heating at elevated temperatures completed the dissolution process so that the species in solution were similar to those found in solutions made from aluminium metal. Solutions seeded with either bayerite or gibbsite crystallised to form only gibbsite. Only crystallisation in the bulk solution and not on the seed surfaces was recorded. In some cases seeding altered the expected crystallisation products, i.e. from gibbsite and bayerite to only gibbsite.     

Crystallization and decomposition of amorphous silicon-aluminium films

The crystallization and decomposition of vacuum-deposited amorphous silicon-aluminium films have been examined by means of transmission electron microscopy. Depending on the aluminium concentration, the transformation of the metastable amorphous phase into the stable phases of aluminium and silicon proceeds by different reactions such as pre-crystallization of aluminium, polymorphous transformation into supersaturated crystalline solid solutions or eutectic decomposition. The temperature dependence of the eutectic crystallization was measured. The results are discussed in terms of the thermodynamics of amorphous-to-crystalline transformation.     

微乳液电纺丝法制备Eu3+掺杂锆酸镧多孔纤维及其发光性能研究

以LaCl₃、ZrClO₂·8H₂O为原料,无水乙醇为溶剂,采用微乳液静电纺丝法制得烧绿石型的锆酸镧纤维,并引入分相剂石蜡在纤维中构筑多孔结构.采用XRD、SEM和BET研究了纤维的结构和形貌,采用PL光谱测试了Eu³⁺掺杂的锆酸镧纤维的发光性能.研究表明,引入分相剂石蜡可以改善纤维中的孔结构,当石蜡用量为4 mL时所制备的锆酸镧纤维物相纯度高,其比表面积为20.77 m²·g^-1,平均孔径19.3 nm,有较为丰富的孔结构且分布均匀.因此,在该纤维中掺杂Eu³⁺后,由于氧离子与稀土离子间的电荷跃迁,以及多孔结构光散射的作用,多孔纤维的发光强度有所提高.     

Effect of different fuels on the alumina–zirconia nanopowder synthesized by sol–gel autocombustion method

In this research, a sol–gel autocombustion route has been proposed to synthesize alumina–zirconia nanopowder, using aluminium nitrate, zirconium oxychloride and various fuels such as citric acid, acetylacetone, oxalic acid and urea. The phase analysis and particle size in the presence of different fuel were compared. The results showed 100% tetragonal phase as well as particle size of 60 nm in the presence of citric acid. FTIR confirms the formation of -Al₂O₃ in corroboration with X-ray studies.     

Low-temperature fabrication and photocatalytic activity of clustered TiO2 particles formed on glass fibers

Clustered anatase phase TiO₂ particles were uniformly formed on the surface of glass fibers by a liquid phase deposition (LPD) method at 60 °C using TiF₄ and H₃BO₃ as the precursors. The clustered TiO₂ particles deposited on the glass fibers and as a photocatalyst these particles not only have a larger surface area than TiO₂ thin films, but also can avoid the disadvantages of using TiO₂ powders encountered in air purification or water treatment. The photocatalytic activity of the sample was evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. The deposition conditions and chemical composition of the clustered TiO₂ particles were discussed. It was found that the clustered TiO₂ particles that formed on the glass fibers obviously showed photocatalytic activity without high-temperature calcination. A formation mechanism was proposed to account for the formation of TiO₂ clustered morphology on the glass fibers.     

水热法合成不同形貌的Bi_2S_3纳米结构

采用水热法在120 ℃反应12 h合成了不同形貌的Bi_2S_3纳米结构.利用XRD、SEM、TEM、HRTEM、SAED等分析方法对产物的结构和形貌进行了表征.结果表明:反应原料对产物的形貌具有重要影响,合成温度取决于矿化剂的选取.讨论了不同形貌Bi_2S_3纳米结构的形成机制,并分析了Bi_2S_3纳米结构的机理.紫外-可见吸收光谱测量表明,相对于正交相Bi_2S_3块体材料而言,由于尺寸效应,所制备的纳米粉体的吸收谱都发生了明显的蓝移.     

Grain refinement in a AlZnMgCuTi alloy by intensive melt shearing: A multi-step nucleation mechanism

Direct chill (DC) cast ingots of wrought Al alloys conventionally require the deliberate addition of a grain refiner to provide a uniform as-cast microstructure for the optimisation of both mechanical properties and processability. Grain refiner additions have been in widespread industrial use for more than half a century. Intensive melt shearing can provide grain refinement without the need for a specific grain refiner addition for both magnesium and aluminium based alloys. In this paper we present experimental evidence of the grain refinement in an experimental wrought aluminium alloy achieved by intensive melt shearing in the liquid state prior to solidification. The mechanisms for high shear induced grain refinement are correlated with the evolution of oxides in alloys. The oxides present in liquid aluminium alloys, normally as oxide films and clusters, can be effectively dispersed by intensive shearing and then provide effective sites for the heterogeneous nucleation of Al₃Ti phase. As a result, Al₃Ti particles with a narrower size distribution and hence improved efficiency as active nucleation sites of α-aluminium grains are responsible for the achieved significant grain refinement. This is termed a multi-step nucleation mechanism.     

The role of fuzzy interfaces in the nucleation, growth and agglomeration of aluminum hydroxide in concentrated caustic solutions

Fundamental crystal growth theory relies on classical concepts of monomeric addition at step sites on crystal surfaces. The nucleation and growth of crystalline aluminium hydroxide from concentrated caustic solutions does not follow classical crystal growth mechanistic pathways. Numerous techniques including static and dynamic light scattering, small angle X-ray and neutron scattering, cryovitirification transmission electron microscopy, rheology and atomic force microscopy have been employed in the study of aluminium hydroxide crystallisation from concentrated caustic solutions. The observations from these techniques have been interpreted on the basis polymer crystal growth theory, thermodynamic phase inversions analysis and entropically driven insolubility.

The experimental observations can be interpreted on the basis that aluminium hydroxide nuclei and crystals are surrounded by a diffuse interface which grades in density from the crystalline aluminium hydroxide particle core to the surrounding solution. A mechanism for the nucleation and growth mechanisms of aluminium hydroxide has been proposed: initial solution formation of a loose polymeric network; clustering of this network followed by gradual densification to form amorphous nuclei; further densification of the core of the nuclei to form crystallites and gradual densification but not crystallisation of the still amorphous diffuse interface.

The presence of this diffuse interface enables the slow agglomeration behaviour of aluminium hydroxides particles in concentrated caustic liquors to be explained. In liquors of very high ionic strength (in this case up to 6 M NaOH) particulate agglomeration would be expected to be rapid due to the small double layer thickness as predicted by DLVO theory. During rapid growth the diffuse interface inhibits the sufficiently close approach of the dense part of the particles to the point where attractive inter-particulate van der Waals forces would dominate and agglomeration would take place. As supersaturation is depleted and the growth rate of the diffuse interface decreases but densification is still occurring the particles can approach more closely and agglomeration will occur. Thus it is probable that the observed agglomeration behaviour is supersaturation and growth rate related.     

Phase separation in highly photosensitive tin-codoped silica optical fibers and fiber preforms exposed to UV radiation

Sn-doped silicate fibers exhibit extremely high photosensitivity when exposed to 248 nm KrF excimer laser. Electron micrograph probing has shown that nanoscale phase separation occurs in fibers and fiber preforms after UV exposure. This phenomenon has been observed only in SnO₂-doped germanosilicate and phosphosilicate fibers and fiber preforms when the SnO₂ concentration is high. At low SnO₂ concentrations no phase separation has been observed. SnO₂ codoped glasses are the first optical fibers to exhibit phase separation.