脉冲激光沉积纳米硅晶粒流体模型的推广

Yoshida等人提出的惯性流体模型只能解释脉冲激光烧蚀制备纳米硅晶粒平均尺寸随环境气压的变化规律.在此模型基础上,考虑到烧蚀粒子的初始速度分布(Maxwell分布),得到了纳米硅晶粒尺寸分布的解析表达式,数值模拟结果与Yoshida等人在不同环境氦气压下制备样品的晶粒尺寸分布的实验统计数据基本相符.还利用修正后的模型对不同环境气体种类(氦、氖、氩)中制备的纳米Si晶粒尺寸分布进行了模拟,模拟结果与实验数据相符.结论可为实现纳米硅晶粒尺寸的均匀可控提供理论依据. 关键词： 纳米硅晶粒 脉冲激光烧蚀 惯性流体模型 尺寸分布     

分子动力学模拟纳米晶体铜的结构与性能

通过分子动力学方法模拟纳米面心立方晶体铜的结构，并对模拟的结果进行了不同晶粒尺寸的纳米晶体的密度、能量分布以及弛豫前后的X射线衍射、径向分布函数等计算.结果表明，大体积分数的晶界和畸变的晶粒是纳米晶体有别于传统的粗晶粒晶体材料结构的重要方面，由此导致纳米晶体一系列不同性能. 关键词：     

SmCo7纳米晶合金晶粒组织热稳定性的热力学分析与计算机模拟

推导出了单相纳米晶合金的晶界过剩体积与晶粒尺寸之间的定量关系, 建立了纳米晶合金的晶界热力学性质随温度和晶粒尺寸发生变化的确定性函数. 针对SmCo₇纳米晶合金, 通过纳米晶界热力学函数计算和分析, 研究了单相纳米晶合金的晶粒组织热稳定性. 研究表明, 当纳米晶合金的晶粒尺寸小于对应于体系中晶界自由能最大值的临界晶粒尺寸时, 纳米晶组织处于相对稳定的热力学状态; 当纳米晶粒尺寸达到和超过临界尺寸时, 纳米晶组织将发生热力学失稳, 导致不连续的快速晶粒长大. 利用纳米晶合金热力学理论与元胞自动机算法相耦合的模型对SmCo₇纳米晶合金在升温过程中的晶粒长大行为进行了计算机模拟, 模拟结果与纳米晶合金热力学模型的计算预测结果一致, 由此证实了关于纳米晶合金晶粒组织热稳定性的研究结论. 关键词： 纳米晶合金热力学 7纳米晶合金')" href="#">SmCo₇纳米晶合金 热稳定性 计算机模拟     

非晶合金Al88Ce2Ni9Fe1回火生成的纳米晶粒度分布与比内表面研究

采用小角X射线散射方法,结合差热分折及广角X射线衍射方法,对新型高强度、高韧性非晶合金Al₈₈Ce₂Ni₉Fe₁回火生成的纳米晶粒度分布和比内表面的改变进行了一系列分析研究,获得了关于纳米晶回转半径、Porod半径、散射积分不变量、粒度分布、结晶度、比内表面等方面的信息. 关键词：     

模拟纳米晶体原子分布及X射线散射理论图案

通过分子动力学方法模拟纳米晶体（1—3nm）的结构．利用模拟的结果，进行了X射线衍射及径向分布函数的模拟计算．结果表明：纳米晶体晶界呈短程有序，界面原子间距分布很宽；随着晶粒尺寸的减小，晶粒的畸变越大，原子体积常数也明显增大 关键词：     

NdFeB纳米复合永磁材料的交换耦合相互作用和有效各向异性

以Nd₂Fe₁₄B/αFe为例，采用立方体晶粒结构模型，研究了纳米复合永磁材料中不同磁性晶粒间的交换耦合相互作用和有效各向异性.纳米复合永磁材料的有效各向异性Keff等于软、硬磁性相各向异性的统计平均值，每个晶粒的各向异性由晶粒表面交换耦合部分和晶粒内部未交换耦合部分的各向异性共同确定.计算结果表明，软、硬磁性相晶粒尺寸分布显著地影响有效各向异性Keff的值.当软、硬磁性晶粒尺寸D相同时，Keff随晶粒尺寸和硬磁性相体积分数的降低而减小, 当D<20nm 时，K 关键词： 纳米复合永磁材料 交换耦合相互作用 有效各向异性 晶粒尺寸     

Fe-Cu-Si-B纳米晶合金的结构与性能

利用非晶晶化法制备了(Fe_0.99Cu_0.01)₇₈Si₉B₁₃纳米晶合金。发现其显微硬度H_v与晶粒尺寸d之间基本服从Hall-Petch关系。利用M?ssbauer谱研究了晶粒尺寸为30nm的材料中类金属原子的分布及其对晶化相电子结构的影响。 关键词：     

纳米晶体微观畸变与弹性模量的模拟研究

采用分子动力学方法模拟纳米晶体铜原子的结构,又对纳米晶体铜原子进行了X射线衍射模拟．计算了晶粒尺寸和点阵畸变,还计算了能量分布和弹性模量等．结果表明不但晶界产生很大的应力场,而且晶粒内部的畸变也起着与晶界相似的重要作用．由于原子半径的增加,导致弹性模量的减少. 关键词：     

CaF2纳米晶粒结构相变行为的尺寸依赖性（英文）

利用原位高压同步辐射X射线衍射方法,对尺寸为11 nm的CaF₂纳米晶粒进行高压结构相变和压缩特性研究。当压力为12 GPa时,观察到由萤石结构向α-PbCl₂结构转变的一次相变,该相变压力点远高于体材料,但略低于粒径更小的CaF₂纳米晶体。相比体材料,纳米尺寸的CaF₂样品的体弹模量更大,说明其更难被压缩。当压力释放至常压时,11 nm的CaF₂纳米晶粒的α-PbCl₂型亚稳相结构被保留下来,相变不可逆。分析了影响11 nm CaF₂纳米晶粒独特高压行为的原因,判定尺寸效应为主要因素,该尺寸下较高的表面能导致结构稳定性增强和体积模量增加。     

超细SnO2纳米晶粒带边光吸收的线度效应

采用超细过滤方法,分别制备含有平均线度小于2nm的超细SnO₂纳米晶粒的酸性和碱性溶胶溶液.通过动态光散射、X射线衍射和晶粒透射电子显微镜像测量,确定了SnO₂晶粒的线度.对其光吸收谱测量发现,超细过滤后酸性和碱性溶胶溶液中晶粒的带边光吸收能量均有明显蓝移.分析结果表明,SnO₂晶粒的线度减小是同类晶粒带边光吸收蓝移的主要原因. 关键词： 超细纳米晶粒 透射电子显微镜 带边光吸收 表面化学修饰     

Estimation of surface area concentration of workplace incidental nanoparticles based on number and mass concentrations

Surface area was estimated by three different methods using number and/or mass concentrations obtained from either two or three instruments that are commonly used in the field. The estimated surface area concentrations were compared with reference surface area concentrations (SA_REF) calculated from the particle size distributions obtained from a scanning mobility particle sizer and an optical particle counter (OPC). The first estimation method (SA_PSD) used particle size distribution measured by a condensation particle counter (CPC) and an OPC. The second method (SA_INV1) used an inversion routine based on PM1.0, PM2.5, and number concentrations to reconstruct assumed lognormal size distributions by minimizing the difference between measurements and calculated values. The third method (SA_INV2) utilized a simpler inversion method that used PM1.0 and number concentrations to construct a lognormal size distribution with an assumed value of geometric standard deviation. All estimated surface area concentrations were calculated from the reconstructed size distributions. These methods were evaluated using particle measurements obtained in a restaurant, an aluminum die-casting factory, and a diesel engine laboratory. SA_PSD was 0.7–1.8 times higher and SA_INV1 and SA_INV2 were 2.2–8 times higher than SA_REF in the restaurant and diesel engine laboratory. In the die casting facility, all estimated surface area concentrations were lower than SA_REF. However, the estimated surface area concentration using all three methods had qualitatively similar exposure trends and rankings to those using SA_REF within a workplace. This study suggests that surface area concentration estimation based on particle size distribution (SA_PSD) is a more accurate and convenient method to estimate surface area concentrations than estimation methods using inversion routines and may be feasible to use for classifying exposure groups and identifying exposure trends.     

Preparation of nano-sized platinum metal catalyst using photo-assisted deposition method on mesoporous silica including single-site photocatalyst

Pt particles in a uniform dispersion were successfully synthesized on single-site photocatalyst (Ti-containing mesoporous silica (Ti-HMS)) under UV-light irradiation by a photo-assisted deposition (PAD) method. Using an aqueous solution of H₂PtCl₆ as a precursor, the nano-sized Pt metal particles were deposited directly on the photo-excited tetrahedrally coordinated titanium oxide moieties within the framework of mesoporous silica (PAD-Pt/Ti-HMS). The Pt catalysts were characterized by means of XRD, Pt L_III-edge XAFS, CO adsorption, and TEM analysis. It was demonstrated that Pt particles had mean diameter of 4 nm in a narrow size distribution. Meanwhile, Pt particles loaded by a conventional impregnation method (imp-Pt/Ti-HMS) showed a wide size distribution ranging from 2 to 30 nm. The PAD-Pt/Ti-HMS catalyst was more active in the CO oxidation than the conventional impregnated imp-Pt/Ti-HMS catalyst. It is suggested that the PAD method using single-site photocatalyst is a useful and unique technique to prepare fine and uniform Pt nanoparticles.     

Influence of synthesis parameters on iron nanoparticle size and zeta potential

Zero valent iron nanoparticles are of increasing interest in clean water treatment applications due to their reactivity toward organic contaminants and their potential to degrade a variety of compounds. This study focuses on the effect of organophosphate stabilizers on nanoparticle characteristics, including particle size distribution and zeta potential, when the stabilizer is present during nanoparticle synthesis. Particle size distributions from DLS were obtained as a function of stabilizer type and iron precursor (FeSO₄·7H₂O or FeCl₃), and nanoparticles from 2 to 200 nm were produced. Three different organophosphate stabilizer compounds were compared in their ability to control nanoparticle size, and the size distributions obtained for particle volume demonstrated differences caused by the three stabilizers. A range of stabilizer-to-iron (0.05–0.9) and borohydride-to-iron (0.5–8) molar ratios were tested to determine the effect of concentration on nanoparticle size distribution and zeta potential. The combination of ferrous sulfate and ATMP or DTPMP phosphonate stabilizer produced stabilized nanoparticle suspensions, and the stabilizers tested resulted in varying particle size distributions. In general, higher stabilizer concentrations resulted in smaller nanoparticles, and excess borohydride did not decrease nanoparticle size. Zeta potential measurements were largely consistent with particle size distribution data and indicated the stability of the suspensions. Probe sonication, as a nanoparticle resuspension method, was minimally successful in several different organic solvents.     

The fluctuation kinetics of formation of nanoparticles: Particle-size distribution

A stochastic simulation of the growth of particles on a uniform cubic lattice was performed by the Monte Carlo method. Changes in the width of the distribution (M _w /M _n ) as the size of particles increased were extremal in character. Distribution narrowing occurred much more slowly than in classic polymerization. An empirical equation relating the number of free vacancies of a growing particle and its mean size was obtained. The introduction of a stabilizer deactivating free vacancies of a growing particle caused the appearance of a critical phenomenon. At stabilizer concentrations higher than critical, large-sized particles could not form. At stabilizer concentrations close to critical, the particle-size distribution was bimodal. This resulted in an anomalously larger distribution width.     

Controlled exfoliation of molybdenum disulfide for developing thin film humidity sensor

We report a facile, size-controllable exfoliation process using an ultrasound-assisted liquid method to fabricate few-layer molybdenum disulfide (MoS₂) nanosheets. The morphology, structure and size distribution of the nanosheets processed with different ultrasonic powers were examined by atomic force microscopy, Raman spectroscopy and dynamic light scattering. It was revealed that the size of nanosheets reduces and final yield increases with elevating ultrasonic power. Bulk and exfoliated MoS₂ based thin film sensors are fabricated by a simple drop casting method on alumina substrates. Our sensors exhibit excellent sensitivity with very quick response and recovery speed to humidity gas. Comparative studies are carried out to draw up the size or ultrasonic power dependent sensing behavior.     

Electrospray of fine droplets of ceramic suspensions for thin-film preparation

An electrostatic atomization technique has been developed to generate ultra-fine spray of ZrO₂ and SiC ceramic suspensions in a range of 4–5 μm with a narrow size distribution (1–9 μm). The aim of this work is to generate fine spray of ceramic suspensions for the preparation of uniform thin films of these ceramic materials on substrates. Thin-film formation using electrostatic atomization process allows one to tightly control the process while meeting the economics in comparison with some other competing process technologies such as chemical vapour deposition, physical vapour deposition and plasma spray, etc. Preliminary results have shown that for low through put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution. It was found that the droplet size of the spray is in the range of a few micrometers with a narrow size distribution and that droplet size and spray current obey theoretical prediction of scaling law. As prepared ZrO₂ and SiC thin films were observed to be homogenous with a particle size of less than 10 μm.     

On-Line Particle Size Analysis Using Ultrasonic Velocity Spectrometry

A new method is described for the determination of particle size distribution of slurries based on ultrasonic velocity spectrometry combined with gamma-ray transmission. This method shares the advantages of ultrasonic attenuation spectroscopy of being capable of analyzing highly concentrated samples without dilution. However the ultrasonic velocity method is better suited to fine particles of diameter from about 0.1 to 30 μm, a greater volume of slurry is analysed and therefore sampling errors are reduced, and precise theoretical models are readily available to permit the accurate determination of size distribution by inversion of ultrasonic velocity measurements. The method can also be used to accurately determine particle size cut points by linear correlation. Using either inversion or correlation methods, the accuracy of particle size information from ultrasonic velocity spectroscopy is significantly enhanced by the independent measurement of solids loading by gamma-ray transmission. In addition, larger sizes can be measured by combining the ultrasonic velocity method with ultrasonic attenuation measurements. The method has been tested in the laboratory on a wide variety of mineral and paint slurries. The method determined the size distribution of single component silica and alumina samples in water in agreement with laser diffraction measurements and the method successfully distinguished well and poorly dispersed TiO₂ suspensions. For composite samples the method discriminated separate TiO₂ and CaCO₃, components and determined their proportions to within 0.25% volume. In addition the method, in combination with ultrasonic attenuation measurements, determined the size fractions of iron ore slurries below 10 and 30 μm to within 1.3% and 1.0% relative respectively, when compared with laser diffraction measurement of particle size. The CSIRO is presently designing an industrial gauge which will be manufactured and installed in an industrial slurry stream in 1997.     

Surface modification of gold nanoparticles and their monolayer behavior at the air/water interface

Gold nanoparticles were prepared by two different methods. The first method was chemically grafting the particles with different lengths of alkylthiol (C₆SH, C₁₂SH and C₁₈SH). For the second method, the Au particles were surface modified first by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups which play a role to physically adsorb cationic surfactant in chloroform. This method was termed physical/chemical method. In the first method, the effects of alkyl chain length and dispersion solvent on the monolayer behavior of surface modified gold nanoparticles was evaluated. The gold nanoparticles prepared by 1-hexanthiol demonstrated the narrowest size distribution. Most of them showed narrower particle size distributions in chloroform than in hexane. For the physical/chemical method, the particles can spread more uniformly on the water surface which is attributed to the amphiphilic character of the particles at the air/water interface. However, the particles cannot pack closely due to the relatively weak particle-particle interaction. The effect of alkyl chain length was also assessed for the second method.     

Quantitative analysis of fine nano-sized precipitates in low-carbon steels by small angle neutron scattering

The small angle neutron scattering (SANS) technique was used to determine the nano-sized precipitates in interstitial free (IF) and low-carbon (LC) steels with a hot-rolling temperature. The real-space direct model fitting method was applied to quantitatively analyze the SANS data. The magnetic and chemical properties of precipitates in the samples were also investigated by separation and comparison of nuclear and magnetic SANS scattering data. The size distribution of precipitates in the IF steel is in good agreement with the microstructure observation using transmission electron microscopy. The results revealed that the IF steel had two types of non-magnetic precipitates, Ti₄C₂S₂ and TiC, with the average size of about 30 nm in diameter and little difference in chemical composition. In case of commercial LC steel, the fine and large precipitates are identified as MnS and Fe₃C, respectively. The average size of spherical MnS precipitates was about 4.8 nm in radius and the distribution is isotropic. It is likely that the LC steels have almost the same composition and a similar size as precipitates such as MnS and Fe₃C with different finishing delivery temperatures. Interestingly, the average size and volume fraction of fine precipitates showed no significantly changes under the different finishing delivery temperatures.