Effect of Grain Size on Phase Transformation and Photoluminescence Property of the Nanocrystalline ZrO_2 Powders Prepared by Sol-Gel Method

Nanocrystalline zirconia （ZrO2） powders were prepared by a sol-gel process followed by annealing treatments from 500 to 1200 ℃. Phase transformation, microstructural features and photoluminescence properties were characterized by X-ray diffraction, transmission election microscopy and photoluminescence spectra, respectively. The results show that both monoclinic phase and tetragonal phase exist in the nanocrystalline ZrO2 powders at annealing temperature in the range of 500-900 ℃, and the concentration of monoclinic phase increases with increasing the annealing temperature. Tetragonal phase is totally transformed to monoclinic phase when annealing temperature is up to 900 ℃. The average grain size of the powders also increases when annealing temperature increases. Two emission peaks centered at 390 nm （named as /390） and 470 nm （named as /470） exist in the photoluminescence spectra, and the intensity ratio of /390 to /470 decreases with increasing annealing temperature. The grain size is proposed to be responsible for the phase transformation in the nanocrystalline ZrO2 powders.     

Blue-shift of Nano-Y_2O_3 : Eu~(3+) Emission Spectra Excited by X-ray

Nano-Y_2O_3:Eu~(3+) powder was prepared by the homogeneous precipitation. With controlling the conditions of the reaction, nano powders with different grain size were obtained. It is found that the blue-shift phenomena exist in the nano-Y2O3:Eu3+ emission spectra excited by X-ray. The wave lengths of the peak (5D0→7F2) are related with the grain size of the powder     

影响喷雾造粒Al2O3/nano-TiO2复合陶瓷粉体流动特性的流变学因素研究

本文研究了分散剂、粘结剂及固相含量等流变学因素对喷雾造粒粉体流动性的影响.结果表明,Al2O3/3wt.%nano-TiO2浆料具有剪切变稀的特性,有利于复合陶瓷粉体的喷雾造粒.当固相含量为浆料总质量的60%,分散剂和粘结剂分别为固相质量的0.3%和1.0%时,浆料具有合适的粘度和最佳的分散稳定性,喷雾造粒所得到的粉体形状为球形或近球形,具有较高的松装密度和良好的流动性,满足用于热喷涂的需要.     

Synthesis and luminescence properties behavior of Eu(3+)-doped nanocrystalline and bulk GdVO4 phosphors by high-energy ball milling and solid state reaction

Europium-doped nanosized-GdVO4:Eu3+ powders and bulk GdVO4:Eu3+ powders were synthesized using a planetary ball mill and conventional solid state reaction method, respectively. The effects of the grain size on the crystallinity, morphology, structure and luminescence spectra were investigated by X-ray diffraction, field emission-scanning electron microscopy and photoluminescence spectroscopy (PL). The room temperature PL spectra of the GdVO4:Eu3+ nanophosphors showed four emission bands at 611, 615, 619 and 595 nm. The bands at 611, 615 and 619 nm were assigned to the 5D0 --> 7F2 transition of the EU3+ ion when excited with 312 nm light.     

纳米TiO2与ACF复合净化室内空气初探

介绍了纳米TiO2负载到ACF上的几种主要方法,分析了单一因素如：TiO2表面羟基含量、晶相组成、薄膜的晶粒尺寸、薄膜的厚度、TiO2／ACF比表面积等对TiO2／ACF吸附光催化净化空气性能的影响,对纳米TiO2与ACF相互作用增强净化效果进行了理论分析,为纳米TiO2与ACF复合方法及相互作用的理论研究和复合材料TiO2/ACF对净化空气的性能研究奠定了一定的基础。     

纳米TiO2掺杂贵金属Pt抑制蓝藻的生长

制备并研究了纳米TiO2和Pt掺杂纳米TiO2对蓝藻生长的影响。结果表明,在太阳光照射下,Pt掺杂纳米TiO2能够破坏蓝藻藻囊;与纳米TiO2相比,Pt掺杂纳米TiO2能够更有效地使蓝藻内叶绿素含量、光合速率和呼吸速率以及超氧化物岐化酶（SOD）活性降低,超氧自由基增多;当Pt掺杂量为1％时,掺Pt纳米TiO2对蓝藻的抑制效果最好。     

溶液pH值对直接沉淀法制备CaF2纳米粉体的影响

以Ca（NO3）2和KF为原料,采用直接沉淀法制备CaF2粉体,借助XRD、SEM、粒径分析方法研究了溶液pH值对产物CaF2粉体晶粒尺寸、颗粒大小及分布的影响,结果表明,在碱性条件下所得CaF2沉淀的晶粒尺寸比在酸性条件下所得CaF2沉淀的小,溶液pH值为13.7时,制备出晶粒大小仅20nm的CaF2纳米粉体。     

纳米BaF2粉体的热稳定性

采用醇/水混合溶剂方法制备了不同粒径的纳米BaF2粉体,研究了粉体的热稳定性.结果表明,纳米BaF2粉体的粒径随着混合溶剂中乙醇含量的提高而减小,粉体的形貌和分散性也都随之改变.根据在不同升温速率下测量的每种粒径纳米BaF2粉体的DSC曲线,由Kissinger方程求出了各晶粒长大激活能.BaF2晶粒长大激活能随着粉体粒径的减小而线性地减小,纳米晶BaF2的热稳定性随着粒径的减小而降低.     

热障涂层陶瓷层材料LnMgAl11O19(Ln=La,Nd)粉体的性能

用共沉淀法制备LaMgAl₁₁O₁₉粉体,证明了提高沉淀温度和pH值可使前驱粉体的性能明显提高。应用差热分析和X射线法研究了磁铅石相的生成温度和粉体的结晶度;使用Scherrer 公式并结合XRD谱计算了晶粒尺寸;用扫描电镜观察了各工艺参数的前驱粉体在1500℃时效5 h后的形貌;使用Malvern ZEN3600粒度仪和Manual measurement软件分析了粉体硬团聚的尺寸分布;用Nd₂O₃, Gd₂O₃, Sm₂O₃替代La₂O₃,研究了制备多种镁基六铝酸盐粉体的可行性。结果表明：在pH值为11.5、沉淀温度为60℃条件下制备的前驱粉体,其完全相变为纯LaMgAl₁₁O₁₉粉体的初始温度为1440℃,比在常温下沉淀的前驱粉体降低了150℃,磁铅石相的生成效率明显提高。在1500℃时效5 h的粉体其晶粒为纳米尺度。提高沉淀温度和pH值有利于减小晶粒尺寸和降低粉体的热导率。采用相同工艺参数可制备出纯NdMgAl₁₁O₁₉粉体,其晶粒尺寸略大于LaMgAl₁₁O₁₉粉体的尺寸。     

Structural and luminescence properties of pure and Al-doped ZnO nanopowders

Pure and Al doped zinc oxide nanopowders have been synthesized by sol-gel route. This is a simple and inexpensive method permitting to obtain a very small grain size powders. Zinc acetate dehydrate was first dissolved in a mixture of 2-methoxyethanol and mono-ethanolamine (MEA) solution, were used as a solvent and stabilizer respectively and doped with a quantity of aluminum nitrate, varying from 0 to 10 mol%. The obtained gel is then calcinated in air at 500 °C. The samples are characterized by XRD, SEM and photoluminescence (PL) studies. The XRD results indicate that pure and Al-doped ZnO powders are solid solutions crystallizing in pure würtzite structure, and consisted of a mixture of nanoparticles with grain size between 23 and 36 nm. The grain size decreases strongly with increasing Al concentration and reaches its lowest value at 5 mol% Al. The PL spectra show that the most important establishment is that the powders show luminescence peaks from green to ultraviolet light, and thus can be used to manufacture transmitters using these emissions. The peaks connected to the blue luminescence are the most intense, and they are generated by transitions involving (Zn_i). The SEM images show a formation of pebbles with sizes decreasing with Al concentration and a morphology evaluating, qualitatively, from pebbles without cavities to highly porous ones.     

Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation     

Dielectric properties of GaN nanoparticles

Three kinds of GaN samples (hexagonal coarse-grain powders, hexagonal nanoparticles and cubic nanoparticles) were synthesized by different methods. The room-temperature frequency spectra of the relative dielectric constant and that of the dielectric loss were measured in the frequency range of 100 Hz to 10 MHz. Analysis of these spectra indicates that the grain size of samples has great influence on the dielectric behavior of samples whereas the crystallography symmetry almost has no impact on the relative dielectric constant.     

Sintering of Doped, Nanocrystalline CeO_2 Powders Prepared under Hydrothermal Conditions

Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm)     

纳米TiO2粉晶的XRD研究

用溶胶－凝胶法制备了纳米ＴｉＯ２粉晶,对不同温度自理的系列粉末用Ｘ射线衍射进行了研究,发现所得粉晶随热处理温度的不同发生了从锐钛矿到金红石相的转变。对系列粉晶进行了Ｘ射线衍射点阵参量计算,结合所得的晶粒度和微结构参数,发现纳米ＴｉＯ２粉晶组元中存在着晶格畸变。     

Grain growth behavior of nanocrystalline Inconel 718 and Ni powders and coatings

Nanocrystalline Inconel 718 and Ni powders were prepared using two approaches: methanol and cryogenic attritor milling. High velocity oxy-fuel (HVOF) spraying of milled Inconel 718 powders was then utilized to produce coatings with a nanocrystalline grain size. Isothermal heat treatments were carried out to study the thermal stability of the methanol milled and cryomilled powders, as well as the HVOF-derived coatings. All nanocrystalline Inconel 718 powders and coatings studied herein exhibited significant thermal stability against grain growth by maintaining a grain size around 100 nm following annealing at 1273 K for 60 min. In the case of the cryomilled nanocrystalline Ni powders, isothermal grain growth behavior was studied, from which the parameters required for the prediction of the microstructural evolution during a non-isothermal annealing were acquired. The theoretical simulation of grain growth behavior of nanocrystalline Ni during non-isothermal annealing conditions yields results that are in good agreement with the experimental results.     

热电材料Bi_2Te_3粉体的制备及粒径分析

为了确定经机械合金化法制备的Bi2Te3粉体进行激光粒度分析的适宜条件,运用X射线粉末衍射、激光粒度分析、比表面积分析等手段对样品物相和粒径进行分析。结果表明,高能球磨30 h后,Bi2Te3晶粒的平均粒径达到本实验中的最小值135 nm;当分散剂采用Tween-80,体积分数为1%;粉体质量浓度为0.01 g/mL时,对样品进行激光粒度分析的结果较为理想。     

Incontinuous grain growth in cobalt nanocrystalline powders prepared by high-energy mechanical milling

Cobalt nanocrystalline powders with the average grain size of about 17 nm were prepared by high-energy mechanical milling. Grain growth in highly pure and particle-containing nanocrystalline Co powders were investigated respectively by a series of annealing experiments at different temperatures. The characteristics of incontinuous grain growth were found in both the pure and the particle-containing nanocrystalline powders. It is proposed by the authors that the sharp increase in nanograin size in the transition between the low and high temperature regions is a result of enhanced grain growth promoted by the stored energy as a supplied driving force, based on which rapid grain growth occurs through a particular dominant mechanism of nanograin rotations in the pure nanocrystalline powders, and that through off-pinning of grain boundaries in the particle-containing nanocrystalline powders.     

粉末粒度对等离子喷涂Al2O3-13%TiO2陶瓷涂层组织结构及性能的影响

等离子喷涂粉末的粒度影响涂层组织结构与性能。选用4种不同粒度的Al2O3-13%TiO2(AT13)粉末等离子喷涂陶瓷涂层,研究了喷涂粉末粒度对涂层组织结构、孔隙率、显微硬度和沉积效率的影响。结果表明:采用较细的喷涂粉末制备的AT13涂层致密、均匀,孔隙率低;随着喷涂粉末粒度增大,涂层的孔隙率增加,显微硬度降低,沉积效率先增后减;采用粒度为38～44μm的粉末喷涂涂层时沉积效率最高,达到51%,涂层组织也较致密,这是等离子喷涂AT13陶瓷层较理想的粒度。     

CuO－SnO_2纳米晶粉料的Sol－Gel制备及表征

不用金属醇盐而以无机盐为起始物质，采用Ｓｏｌ－Ｇｅｋ法得到了平均晶粒尺寸为２１～２２ｎｍ，ＣｕＯ掺杂的ＳｎＯ_２粉料；运用Ｘ射线衍射（ＸＲＤ）、差热—失重分析（ＤＴＡ－ＴＧ）、透射电镜（ＴＥＭ）及ＢＥＴ比表面（ＳＡ）测定等分析手段对粉料进行了表征．实验表明，ＣｕＯ的掺杂抑制了ＳｎＯ_２晶粒的生长；以无机盐为原料，采用Ｓｏｌ－Ｇｅｌ法制取ＳｎＯ_２（ＣｕＯ）纳米级晶料是切实可行的，将有利于产业化．     

制备条件对ZrO_2超细粒子尺寸及分布的影响

本文采用胶体－超临界流体干燥法制备纳米级ＺｒＯ２超细粉料，用透射电镜（ＴＥＭ）、比表面积（ＢＥＴ）和粒度分析法对颗粒尺寸进行观察和测定，并详细考察了制备条件对产品粒子粒度及其分布的影响