纳米相铁电PbTiO3超微粉的相变特性

通过溶胶－凝胶工艺和水解老化过程制备了纳米相钛酸铅超微粉。经过ＸＲＤ分析精确地确定了晶格常数晶粒尺寸。ＰｂＴｉＯ３超微粉的相变采用不同升温速率的ＤＳＣ分析和ＳＨＧ分析，得到了相变温度与晶粒尺寸的关系。结果表明：ＰｂＴｉＯ３的晶粒尺寸位于１０－１００ｎｍ范围，相变温度比体材料要低，并且相变区域被展宽，认为小晶粒尺寸可能是导致相变区域展宽的原因。最后将纳米相ＰｂＴｉＯ３微粉的相变与弛豫型铁电体的扩散相     

正丁醇钛—乙酸钡水解法合成BaTiO3粉体的研究

本文着重研究了Ｔｉ（Ｏ＾ｎＢａ）４－Ｂａ（ＤＡｃ）２水解法合成高纯超细ＢａＴｉＯ３粉体的制备工艺。借助ＴＧＤＴＡ，ＸＲＤ，ＴＥＭ，ＳＥＭ，ＳＡＸＳ和ＩＣＰ－ＡＥＳ等分析手段，研究了ＰＨ值，Ｂａ／Ｔｉ比和（Ｂａ／Ｔｉ）比，反应温度，浸泡处理等对ＢａＴｉＯ２粉体性能的影响，采用本工艺方法合成的ＢａＴｉＯ３粉体，纯度达９９．８０ｗｔ％，比表面积为６８ｍ＾２／ｇ，一次粒子平均粒径４６．７ｎｍ，二次粒子粒径     

柠檬酸盐法合成γ—LiAlO2超微粉

以ＬｉＮＯ３，Ａｌ（ＮＯ３）３．９２ＨＯ和柠檬酸为原料合成γ－ＬｉＡｌＯ３超微粉。对合成的材料进行了ＴＧ，ＤＴＡ，ＸＲＤ和ＴＥＭ等表征，结果表明，焙烧温度在５５０℃以试样基本恒重。５６２℃有一相变峰，生成纯相γ－ＬｉＡｌＯ２超微粉。     

酞侧基聚芳醚酮冲击断裂韧性的研究

本文用仪器化冲击仪研究了酞侧基聚芳醚酮（ＰＥＫ－Ｃ）的冲击断裂韧性对温度的依赖性。依据线弹性断裂力学原理，通过１．５ＹＰＬ／ＢＤ２对ａ－１／２作图，所得直线斜率即为应力强度因子Ｋｃ；用Ｕ对ＢＤΦ作图，所得直线斜率即为扩展裂纹所需的能量Ｇｃ。在不同温度下测试，便可得到Ｋｃ－Ｔ，Ｇｃ－Ｔ的依赖关系图。温度对冲击断裂韧性的影响，是ｔａｎδ损耗和裂尖前缘热钝化共同作用的结果。在１００～１４０℃之间，断裂韧性的升高主要是由于β转变作用的结果。通常ｔａｎδ对能量吸收过程的影响，要比裂尖前缘热钝化的影响小，只有当裂尖前缘区域的有效温度Ｔｅ低于软化温度Ｔｓ时，ｔａｎδ才起作用。当Ｔ＝１８０℃，Ｔｅ＝２０２．４３℃，大于软化温度Ｔｓ时，裂尖前缘热钝化开始起作用，冲击断裂韧性随温度升高而升高     

香烟滤材聚丙烯接枝共聚物结构与物性的研究

用热失重（ＴＧ）法分析了ＰＰ与ＰＰ－ｇ－Ｍ（聚丙烯接枝共聚物）的热稳定性，ＴＧ曲线表明：ＰＰ－ｇ－Ｍ的热稳定性比ＰＰ高，不仅它们的分解温度有所提高（提高１４．２℃～７５．５℃），而且分解速率下降（分解温度范围从３６℃扩展到５４．６℃～８８．４℃）；用ＤＳＣ示差扫描测定ＰＰ和ＰＰ－ｇ－Ｍ的熔点（Ｔｍ）、熔融热焓（△Ｈｍ），发现ＰＰ与ＰＰ－ｇ－Ｍ的Ｔｍ基本相同，略有降低（约１．５℃～４．５℃），△Ｈｍ随着结晶度（Ｘｃ）降低而降低，降低２７．４Ｊ／ｇ～５１７Ｊ／ｇ；用Ｘ射线衍射分析ＰＰ和ＰＰ－ｇ－Ｍ的Ｘｃ和晶面距，发现ＰＰ－ｇ－Ｍ的Ｘｃ较ＰＰ低（约降低２．５％～１０．５％），晶面距基本相同，即ＰＰ与ＰＰ－ｇ－Ｍ的晶胞大小相同，说明ＰＰ的接枝物聚集在ＰＰ的非晶区     

PLZT陶瓷的介电弛豫行为与A位有序

用传统粉末工艺合成了（Ｐｂ＿（０．８６５）Ｌａ＿（０．０９））（Ｚｒ＿（０．６５）Ｔｉ＿（０．３５））Ｏ＿３陶瓷（ＰＬＺＴ９／６５／３５）。Ｘ射线研究表明：试样中存在着Ａ位准体心立方有序超结构，有序畴的平均尺寸为１０～２０ｎｍ。测定了１０个频率下介电常数与温度的关系，并将介电常数最大值的温度Ｔ＿ｍ与对应的频率ｆ用Ｖｏｇｅｌ－Ｆｕｌｃｈｅｒ公式拟合，得到物理上合理的激活能及指数前项值，这表明试样的介电弛豫行为与自旋玻璃态类似。基于Ａ位有序超结构及类似于自旋玻璃态的极化行为，对试样的极化全过程进行了探讨。     

HAN-TEAN-H_2O 三元体系的相变及其相图

用ＤＳＣ研究了ＨＡＮ－ＴＥＡＮ－Ｈ２Ｏ三元体系的低温热行为，建立了该体系低温下相变与组分关系的相图。考察了玻璃化转化温度随ＨＡＮ／ＴＥＡＮ比例的变化规律。发现了三元体系的溶液性质在ＨＡＮ－ＴＥＡＮ比率较大时，与ＨＡＮ－Ｈ２Ｏ二元体系相似，而在ＨＡＮ／ＴＥＡＮ比率较小时，则与ＴＥＡＮ－Ｈ２Ｏ二元体系相似。     

螺旋霉素从水溶液中结晶成核动力学

通过测量在不同的加热速率下的最大过热温度得到了螺旋霉素在水溶液中结晶成核的动力学，实级成核速度ｍＮ．ｐ＝７．０８９ｅｘｐ「－１７．９９８×１０＾３（１／２９８．１５－１／Ｔ）．ｅｘｐ（－０．１１９／ｌｎ＾２ｓ）二次成核速率ｍＮ，ｓ＝０．３４１ｅｘｐ」－３．５０８×１０＾３（１／２９８．１５－１／Ｔ」．（ｃ－ｃａ）＾１．３９２并和光散射方法测定估计出初级晶核的大小约为０．０５μｍ。     

SBS／L／—PB／TEGDA（TMPTA）光敏体系的透光性和感光特性

本文在研究了ＳＢＳ／Ｌ／－ＰＢ／ＴＥＧＤＡ（ＴＭＰＴＡ）均相光敏体系对特定光源（低压汞灯，λ＝２５４ｎｍ）发射光吸收的基础上，按剩余膜产率（Ｙ）绘制出感光特性曲线（Ｙ－ｔ）确定出Ｙ随Ｌ－ＰＢ和ＴＥＧＤＡ（或ＴＭＰＴＡ）用量变化的规律，求算了优选体系的量子产率，以剩余膜产率和灰梯度尺法测定了上述体系的相对感度。     

CaO—Al2O3—SiO2系烧结微晶玻璃的初始相变

本文采用ＸＲＤ和ＳＥＭ对ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２系烧结微晶玻璃的初始相变进行了分析，测定了具有不同起始颗粒尺寸的玻璃的析晶Ｃ曲线。实验结果表明，玻璃的初始相变与玻璃粘度，烧结温度和颗粒尺寸有关，在不同温度区域烧结，析晶的孕育期不同，高温区烧结对析晶有抑制作用。     

钛酸铅热力学及其铁电相变的研究

在不同边界条件下，考虑到钛酸铅的晶粒界面能和表面自由能，利用广义的Ｃｌａｕｓｉｕｓ－Ｃｌａｐｅｙｒｏｎ关系式以及Ｌａｎｄａｕ－Ｇｉｎｓｂｕｒｇ－Ｄｅｖｏｎｓｈｉｅ热力学方程，求得了在不同受力状态，薄膜厚度及超微粒子的晶粒尺寸与自发极化强度和铁电相变温度之间的关系，理论分析能够很好地解释实验现象，综合文献的报道，对钛酸铅的铁电物性给予了全面的总结。     

Nanoscale potassium niobate crystal structure and phase transition

Nanoscale potassium niobate (KNbO₃) powders of orthorhombic structure were synthesized using the sol-gel method. The heat-treatment temperature of the gels had a pronounced effect on KNbO₃ particle size and morphology. Field emission scanning electron microscopy and transmission electron microscopy were used to determine particle size and morphology. The average KNbO₃ grain size was estimated to be less than 100 nm, and transmission electron microscopy images indicated that KNbO₃ particles had a brick-like morphology. Synchrotron X-ray diffraction was used to identify the room-temperature structures using Rietveld refinement. The ferroelectric orthorhombic phase was retained even for particles smaller than 50 nm. The orthorhombic to tetragonal and tetragonal to cubic phase transitions of nanocrystalline KNbO₃ were investigated using temperature-dependent powder X-ray diffraction. Differential scanning calorimetry was used to examine the temperature dependence of KNbO₃ phase transition. The Curie temperature and phase transition were independent of particle size, and Rietveld analyses showed increasing distortions with decreasing particle size.     

Charge Distribution of Incipient Flame-Generated Particles

We report the size and electrical charge distributions of incipient nanoparticles generated in atmospheric pressure hydrocarbon/air premixed flames in conditions prior to the onset of soot particles. The particle size and charge distributions are measured by Differential Mobility Analysis (DMA) and compared to theoretical charge distributions predicted for flame conditions. The results show that the charge distribution attained in flames is well predicted by Boltzmann theory for all particles, including even the smallest incipient particles with diameters in the 1–3 nm size range. In flame conditions that produce only particles smaller than 3 nm, the charge fraction of particles agrees with that predicted by Boltzmann theory near the flame temperature (1700 K). In flame conditions with ‘bimodal’ particle size distributions, the charge fraction of the smallest particles agrees with the Boltzmann prediction at maximum flame temperature, while the charge fractions of larger particles agree with Boltzmann theory at temperatures that coincide with the local temperature near the probe surface (1000–1200 K). The results of this paper show that the temperature of the Boltzmann charge fraction that best agrees with the measured charge fraction for each particle size gives the local temperature of their last coagulation event. The smaller particles, which retain their charge fraction predicted by Boltzmann at the maximum flame temperature, do not thermalize by coagulation in the cool region near the probe evidencing low probability for charge transfer as well as for coagulation.     

PbTiO_3纳米粉体粒度的可控合成

以Ti(OC4H9)4、醋酸铅作为原料,在水热体系内首先合成具有2~5 nm尺寸的非晶态PbTiO3,将得到的产品进行退火处理,用XRD、TEM等测试手段对产品进行表征,结果表明在600℃时退火得到的PbTiO3纳米粉体为平均粒径在30 nm左右,没有明显的团聚现象出现。800℃时其平均粒径增加至80 nm左右,粒径分布范围变宽,而且发生严重的团聚。物质的结构从非晶态转化为四方结构。     

Size effects on χ- to α-Al2O3 phase transformation

Nano-scaled χ-Al₂O₃ powders with d₅₀ mean particle sizes from 17 to 314 nm were prepared to investigate the size effect on their phase transformation. Structural properties and crystallization behavior as a function of thermal treatments of various-sized χ-Al₂O₃ particles were examined by DTA, XRD and TEM characterizations. It was confirmed that the decrease of particle size allows for stable α-Al₂O₃ formation at relatively low temperature. Furthermore, the phase transformation route of χ-Al₂O₃ to α-Al₂O₃ was also modified due to the decrease of particle size. A critical size of χ-Al₂O₃ that determines the phase transformation behavior was found to be around 40 nm. For particles larger than 40 nm, a transition phase of κ-Al₂O₃ is formed before obtaining final α-Al₂O₃ phase. Nevertheless, for those smaller than the critical size, starting χ-Al₂O₃ particles have to grow to 40 nm and then directly transform to α-Al₂O₃ bypassing κ-Al₂O₃ at a temperature as low as 1050 °C.     

Cluster Size Determination in the Chemical Vapor Deposition of Aluminum Nitride

Aluminum nitride was prepared in a laminar-flow, tubular reactor using an atmospheric pressure chemical vapor deposition (APCVD) method at a reaction temperature ranging from 700° to 1100°C and AlCl₃ and NH₃ concentrations of 0.4 and 8 mol%, respectively. Films grew on the reactor wall and particles formed in the gas phase. The production rates of films and particles were independently determined. A comprehensive model was constructed to estimate the molecular size of the growth species in the APCVD process to simultaneously form films and particles of AIN from AlCl₃, and NH₃. Transport equations of a dominant growth species used in growing films on the reactor wall and particles in the gas phase in a laminar-flow, tubular reactor were formulated and solved. An assumption made in the model was to use the surface reaction rate constant measured for the film surface for the particle surface. Comparing the film and particle growth data measured experimentally with those obtained from model prediction allows us to conclude that the growth species are clusters ranging in size from 0.8 nm at 700°C, equivalent to 8 units of AIN, to 0.5 nm at 1100°C, equivalent to 1 unit of AIN.     

Tetragonal-to-Cubic Structural Phase Transition in Pollucite by Low-Temperature X-ray Powder Diffraction

The tetragonal-to-cubic structural phase transition in pollucite (CsAlSi₂O₆) was investigated using low-temperature X-ray powder diffraction in the temperature range of 93 to 298 K, and the lattice constants were refined with Rietveld analysis. It was found that CsAlSi₂O₆ had a tetragonal phase with a space group of I 4₁/acd in the temperature range of 93 to 248 K, a = 1.36337(4) nm, c = 1.36988(6) nm at 248 K, and underwent a phase transition from tetragonal to cubic with a space group of Ia-3 in the temperature range of 248 to 273 K, a = 1.36645(3) nm at 273 K.     

络合溶胶-凝胶法制备Al_2O_3纳米晶及其表征(英文)

以异丙醇铝为原料,用聚乙二醇(PEG1000)络合溶胶-凝胶法合成了Al2O3纳米晶,并采用差热-热重分析、X射线衍射、透射电子显微镜等对络合前驱体及粉体进行表征;探讨了PEG1000及煅烧温度对纳米Al2O3相结构、粒子尺寸、形貌及分散性的影响规律.结果表明:PEG1000增强了纳米Al2O3粒子的分散性.干凝胶在600～900℃煅烧后得到γ-Al2O3相;在600℃煅烧条件下,得到γ-Al2O3粒子形貌为针状结构,长度约为50～60nm.随着煅烧温度的升高,γ-Al2O3针状粒子长度逐渐减小,在750℃煅烧后,得到γ-Al2O3粒子长度为20～30nm;在900℃煅烧条件下,γ-Al2O3粒子形貌为颗粒状,平均粒径尺寸为10nm;当干凝胶在1 000℃煅烧后得到θ-Al2O3和α-Al2O3的混合相,所得粒子平均粒径尺寸为20 nm;当干凝胶在1 200℃煅烧后,得到的Al2O3全部转化α-Al2O3相,制得的纳米Al2O3粒子尺寸均一且分散性良好.     

Synthesis and characterization of PNIPAM/PS core/shell particles

Crosslinked, monodisperse PNIPAM particles were synthesized by precipitation polymerization. The particle size was measured by dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), and transmission electron microscopy (TEM). Two different polymerization methods were used to prepare PNIPAM/PS core/shell particles, both above and below the volume phase transition temperature (VPPT) using either a semibatch or seeded semibatch polymerization process. In both processes, uniform “raspberry” structures were obtained in which polystyrene formed small domains on the surface of the PNIPAM particles. The resulting core and shell structure was confirmed by temperature‐dependent particle size and density gradient experiments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Finite size effects in submicron barium titanate particles

An experimental and theoretical analysis of finite size effects in submicron barium titanate particles is presented. The dielectric data show that the dielectric constant (ε = 734) of small particles (d = 20 nm) remains very similar to that of single crystals provided that the particles are grown from an amorphous phase and not mechanically crushed into powder. This shows that what has in the past been mistaken for true size effects (i.e., depolarization fields) is due to lattice strain. The X-ray data show that the Curie temperature (cubic-tetragonal transition temperature) decreases monotonically to zero degree Kelvin as particle size is reduced. However this is shown to be a simple function of lattice constant: The lattice constant expands as the particle diameter d contracts. This is similar to surface relaxation in thin films.