Shape Estimation of Anisometric Particles Using Size Measurement Techniques

This study was conducted to establish a simple method for evaluating the morphology of fine anisometric particles using size measurement techniques. The size distributions of mica particles and carbon fibers classified into narrower size ranges were measured by gravitational sedimentation and laser diffraction techniques. The ratio of mean diameters determined for flaky particles strongly depended on the aspect ratio, i.e. flatness. The relationship between particle shape and diameter is discussed theoretically. The experimental results were similar to those predicted. The flatness of fine particles can be evaluated by the ratio of the median diameter determined by laser diffraction to that determined by sedimentation.     

Characterization of Fibres and Fibre Collectives with Common Laser Diffractometers

The method described utilises the effect that in many commercially available laser diffractometers a laminary flow of the suspension medium in the measurement cell exists. However, data analysis carried out using commercially available laser diffractometers is normally based upon the assumption that there is a statistical orientation of the particles in the measurement volume. The resulting diffraction patterns are, therefore, assumed to be centrosymmetric and ring‐shaped. As a consequence, the detectors commonly used only record parts of the diffraction patterns. Based upon these assumptions, it is accepted that grain size analysis of fibrous particles gives an equivalent diameter between length and diameter. First experiments carried out using a Malvern Mastersizer X showed that fibres align in the flow direction. Analysis of the entire diffraction pattern should, therefore, provide information about the length and diameter of the fibres.     

Structure determination of surface magic clusters

The structure of a type of surface magic cluster is determined by a combination of scanning tunneling microscopy, density-functional calculations, and dynamical low energy electron diffraction. The diffraction method is applicable because these clusters created through hierarchical self-organization of Ga deposited onto a Si(111)-7x7 surface have identical size and structure and form an ordered array with exact translational symmetry. The unprecedented detailed structure information provided by the diffraction measurement is consistent with direct microscopic imaging and theoretical calculations.     

Laser Diffraction Spectroscopy: Influence of Particle Shape and a Shape Adaptation Technique

The evaluation algorithm employed in laser diffraction spectroscopy is usually based on the Fraunhofer diffraction theory for spheres. As this evaluation theory is limited to spheres only, the measurement of irregularly shaped particles results in errors in the evaluated particle size distribution. To determine the influence of the particle shape, measurements of arbitrarily shaped particles were simulated, evaluated and compared with results for spherical particles of the same projected area. The detailed investigations showed that the particle's microstructure, i.e. its surface roughness, has almost no or only a negligible effect on the measurement result. In contrast to this advantageous outcome, the particle's microstructure, i.e. its axis ratio, affects the measurement result greatly and must be taken into account in the evaluation method. Based on these results, particles were considered to be ellipsoids with specific (but negligible) surface structures and a mathematical adaptation method was developed by extending the evaluation theory from spheres to randomly in space oriented ellipsoids. Simulations and experiments with reticles verified the need for this adaptation technique and its efficiency when applied.     

Formation of fractal structures by aggregation of anisometric iron (III) hydroxide particles

Coagulation of anisometric iron (III) hydroxide sols has been studied by dynamic light scattering, TEM and ultra-small-angle X-ray scattering. The anisometry of rod-like individual colloidal particles can be characterised with a mean aspect ratio of 10. It was established for the first time, that the aggregates formed by coagulation of anisometric particles show definite fractal structure with a mass fractal dimension of 1.95 ± 0.05.     

液滴微粒直径分布的激光散射法测量

本文利用氦氖激光器为光源在自行设计的光散射实验装置上对球形微粒群进行了粒径平均直径及直径分布的理论研究和测量.实验结果表明,本实验装置具有测量精度高、适用范围广和测量粒径范围宽等特点.     

激光衍射微粒测量中的独立模式反演算法

在用激光衍射法测量微粒直径及其分布时得到的矩阵方程组是一组病态方程 ,无法直接求解。目前大多数求解方法是采用已知模式的拟合算法。但由于在实际中的微粒直径的分布是多种多样的 ,因此难以用一种或几种分布函数去近似描述。试图从微粒衍射的特征着手提出一种未知分布的独立模式的求解方法     

Controlled Formation of Patchy Anisometric Fumed Silica Supraparticles in Droplets on Bent Superhydrophobic Surfaces

This article presents a study on the formation of anisometric, ellipsoidal supraparticles by evaporation‐induced self‐assembly from multicomponent colloidal dispersion droplets deposited on a superhydrophobic surface. Performing the formation process on bent surface substrates grants precise control on the shape and spatial orientation of the final dried supraparticles. Due to the V‐shaped surfaces providing interfacial blockage, anisotropic evaporation rates occur with respect to the direction of the bending channel. This proportionally leads to inhomogeneous accumulation of fumed silica (FS), used as structure guiding component. Thus, upon the increase of FS‐particle interaction via ionic strength (NaCl), this so‐formed shell provides enough anisotropic stiffness resulting in predictable droplet deformation with the elongation orientation being perpendicular to the bending axis. The anisotropic evaporation rates were monitored and quantified using an established, empiric kinetic model and taking into account surface geometry. Employing this reliable control of elongation direction and using additional Fe₃O₄@SiO₂ core–shell nanoparticles, anisometric magnetic Janus supraparticles with defined patch position were prepared, which are not accessible on flat surfaces. The results can find application in the controlled, easy to scale up, nanofabrication process of patchy anisometric supraparticles.     

Development of a Mathematical Model for Light Scattering by statistically irregular particles

A mathematical model is described to predict Fraunhofer diffraction by statistically irregular particles. It is demonstrated that the particles are characterised by a probability distribution of radius and a correlation function in the surface. The results of calculation show that at angles not too far from the forward scattering direction and for irregularity heights within a limited range, the irregular particles may be represented approximately by spheres with a size distribution equal to the probability distribution of radius. However, the calculations are highly sensitive to the exact nature of the probability functions. Comparisons of the results with those of a simpler model are not satisfactory beyond the first forward scattering lobe.     

Diffraction Patterns of Static Particles on a 2-D Surface

The diffraction patterns of static particles deviate from those of dynamic particles of the same distribution characteristics. Use of diffraction solutions based on independent scattering to analyse such diffraction patterns leads to a narrower size distribution biased towards the smaller sizes. A 2-D coherent diffraction model using an inter-particle relation PDF function is developed. The model clearly demonstrates the terms due to the individual particle diffraction and the terms contributed by the inter-particle correlation, i.e. the coherent effects. The deviation of the static particle diffraction pattern from that of the dynamic particles can be well predicted. The results of this study provide a general solution for utilizing the forward diffraction technique in static particle measurement. One of the important applications of the new model is in the development of a diffraction reference reticle used for diffraction-based particle sizing instruments verification.     

Threshold and Lennard-Jones resonances and elastic lifetimes in the scattering of atoms from crystalline surfaces

In this paper we apply the GR method for solving the scattering equations of atoms from a hard corrugated surface, on accelerated particles above a hard corrugated surface and a hard corrugated surface with an attractive well. The solutions are given for the Rayleigh hypothesis that under the range of corrugation presented in this paper leads to the exact ones. Threshold resonances are studied observing that the appearance and disappearance of beams must be for a general theory with vertical tangent. The structure of the Lennard-Jones resonances given for the model mentioned above. For the first time it is stressed that Lennard-Jones resonances are not observed in metal surfaces in general, and, accordingly, they are unobserved in compact metallic surfaces. This is correlated with the fact that diffraction has not been observed. Both facts are due to the very weak corrugation of the gas-metal interaction potential. According to our results, the Lennard-Jones resonances in metals present greater difficulties to be observed experimentally. We also note that the absence of diffraction in compact metal surfaces is because they are almost plane and not because of the Debye-Waller effect. Finally, we have calculated the lifetimes of the atoms at the crystal surfaces. These are larger, the smaller the incident energy and the larger the corrugation. But the lifetimes are particularly large at resonance condition (10^?11 s).     

采用紫外光照法在磷酸盐玻璃中合成CdS/Ag复合微粒

掺杂有Ⅱ-Ⅵ族半导体纳米颗粒(如CdS)或者过渡金属(如Ag)的玻璃由于其较大的非线性光学效应而引起人们的极大兴趣,而同时掺杂有半导体/金属的复合微粒则可以进一步增强玻璃的三阶非线性效应,因此成为目前的研究热点。我们利用玻璃沉淀技术及随后的热处理和紫外光还原技术制备了含高浓度(1%)Ag微粒的玻璃,并采用X射线衍射分析了其物相,用高分辨扫描电镜分析了其形貌,以及测试了其吸收和发光性能。从CdS/Ag复合微粒的扫描照片可以发现晶粒均匀分布在玻璃中,尺寸约为1μm。X射线衍射发现经过热处理和紫外光照的样品衍射峰中含有CdS和Ag,而只进行热处理的样品则只含有CdS,未处理的样品则显非晶态。CdS/Ag复合微粒的吸收峰呈现典型的表面等离子共振峰(420nm)以及CdS的峰(600nm),只含有CdS微粒的样品的吸收峰则在480nm附近,未处理的样品在320nm附近有一个吸收峰,这可能是由于样品在快速冷却过程中的微小晶化造成的。只含有CdS微粒的样品有三个明显的发光峰,然而CdS/Ag复合微粒的发过峰则消失。我们提出了共振能量转移机制来解释该现象。讨论了紫外光照还原Ag微粒的机制。可以认为通过紫外光照,CdS表面的电子被激发出来还原Ag+,从而形成银颗粒,伴随着空穴则被表面缺陷所捕获。     

F等离子体刻蚀Si中Lag效应的分子动力学模拟

通过分子动力学模拟的方法对感应耦合等离子体刻蚀中Lag效应的产生机理进行了研究. 研究结果表明,在刻蚀过程中普遍存在Lag效应,宽槽的刻蚀率明显比窄槽的刻蚀率要高,这是由于宽槽更有利于产物从槽中的逸出;窄槽中产物从槽中逸出的速率较低,较多的产物拥挤在窄槽中降低了入射的F等离子体入射的速度,从而降低了F等离子体到达Si表面的能量,而相同条件下,刻蚀率随能量的降低而降低;另一方面,窄槽中入射的等离子体与槽壁的距离较近,使得入射的F更容易与槽壁表面的Si的悬挂键结合沉积在槽壁表面,使刻蚀出的槽宽度变窄,进一步影响到后继粒子的入射;Lag 效应随槽宽的减小而增强,随温度的升高而减弱,随入射粒子能量的升高而增强. 关键词： 分子动力学 Lag效应 刻蚀 刻蚀率     

Particle size analysis: A comparison of various methods ii

In previous work, the relative performance of various methods used to characterize the particle size distribution of powders composed of fine irregularly shaped particles was assessed. It was found that methods employing Fraunhofer diffraction theory were inferior with respect to particle counting methods. Furthermore, calculated particle size distributions varied considerably between manufactures of Fraunhofer devices. It is well known that the Mie optical model can also be used to analyze the data collected by laser diffraction instruments. Here, we have compared particle size distributions collected using two Laser diffraction instruments to those determined by the Aerosizer. In our earlier work the Aerosizer was shown to produce results nearly identical to those determined by image analysis. The results of this study indicate that the use of the Mie optical model does not correct for deficiencies previously noted for laser diffraction methods. Considerable variation exists between the results obtained on laser diffraction instruments manufactured by different companies. Our earlier recommendation to use extreme caution when employing laser diffraction instruments to characterize fine powders continues to be supported in the present work.     

Changes of Separation Status During Registration and Scattering

In our previous work, a new approach to the notorious problem of quantum measurement was proposed. Existing treatments of the problem were incorrect because they ignored the disturbance of measurement by identical particles and standard quantum mechanics had to be modified to obey the cluster separability principle. The key tool was the notion of separation status. Changes of separation status occur during preparations, registrations and scattering on macroscopic targets. Standard quantum mechanics does not provide any correct rules that would govern these changes. This gives us the possibility to add new rules to quantum mechanics that would satisfy the objectification requirement. The method of the present paper is to start from the standard unitary evolution and then introduce minimal corrections. Several representative examples of registration and particle scattering on macroscopic targets are analysed case by case in order to see their common features. The resulting general Rule of Separation Status Changes is stated in the Conclusion.     

Implementation of the Laser Diffraction Technique for Acoustic Cavitation Bubble Investigations

Knowledge of the acoustic cavitation cloud would be useful for improving ultrasound reactor design. Among the characterisation techniques, few are adapted to bubble investigations in an intense ultrasound field. Some problems raised by these measurements result from interactions between the acoustic pressure wave and the measuring light wave. This paper reports the implementation of the laser diffraction technique to determine the size and volume concentration of bubbles generated by a dipping horn operating at 20 kHz. Measurements were performed with a Malvern 2600 instrument. The size distribution, deduced from the diffraction pattern scattered by the bubble cloud crossed by a laser beam, is disturbed by the acoustic pressure wave involving deviation of a light beam at low diffusion angles (acousto‐optic effect). A bubble size correction procedure based on the subtraction of the light energy due to the ultrasound wave is described. The size measurements, and thus the correction procedure, were validated by a second laser technique based on a different measuring principle: phase Doppler interferometry. The measurement reliability was further confirmed by an original application of laser diffraction based on measurements performed just after sonication. These three methods lead to a mean bubble size (Sauter mean diameter) of about 10 μm at a high ultrasound power input. Concerning the void fraction, only measurements achieved after sonication and by laser diffraction predict a correct estimation of this parameter.     

In-Line Particle Size Determination for Jet Agglomeration Processes

In jet agglomeration plants, powders are agglomerated to obtain good instant properties. The free-falling initial material is wetted in a spray cone by droplets or in a steam jet by condensation at the particle surface. In a subsequent region of high particle concentration, collision between particles occurs and agglomerates form, if the forces of adhesion are strong enough. A commercial measurement device, working according to the principle of Fraunhofer diffraction, was modified for in-line application. It was used to measure particle size distributions and concentrations of solid particles and droplets in jets. A model is presented to calculate local particle sizes by means of mass balances from integral measurements over large volumes. The results of in-line particle size and agglomerate size analyses show the practical importance of dry agglomeration during transport and lead to a better understanding of the subsequent wet agglomeration process.     

Preparation of Reinforced Anisometric Patchy Supraparticles for Self-Propulsion

The preparation of fumed silica-based anisometric supraparticles with well-defined catalytically active patches suitable for self-propulsion is presented here. These sub-millimeter-sized particles can self-propel as they contain Pt-covered magnetite (Fe₃O₄) nanoparticles, where the Pt can decompose catalytically a “fuel” like H₂O₂ and thereby propel the supraparticles. By their magnetic properties, the catalytically active nanoparticles can be concentrated in patches on the supraparticle surface. The goal is to obtain robust supraparticles with well-defined patchiness and long-time stability during self-propulsion through evaporation-induced self-assembly (EISA) on a superhydrophobic surface. The latter is a major issue as oxygen evolution can lead to the disintegration of the supraparticles. Therefore, enhanced mechanical stability is sought using a number of different additives, where the best results are obtained by incorporating polystyrene microspheres followed by heat treatment or reinforcement with microfibrillated cellulose (MFC) and sodium trisilicate (Na₂SiO₃). The detailed internal structure of the different types of particles is investigated by confocal micro-X-ray fluorescence spectroscopy (CMXRF), which allows for precisely locating the catalytic Fe₃O₄@Pt nanoparticles within the supraparticles with a resolution in the µm range. The insights on the supraparticle structure, together with their long-time stability, allow fabricating optimized patchy supraparticles for potential applications in propulsion-enhanced catalysis.     

Superlattices of lamellae in microporous oriented polyolefine films

The structure and mechanism of the formation of superlattices lamellae in microporous polyolefine (polyethylene and polypropylene) films obtained by polymer melt extrusion followed by annealing, uniaxial extension, and thermal fixation stages have been studied by scanning electron and atomic-force microscopy. It has been shown that oriented anisometric particles, i.e., lamellae aggregates, are formed in films as the spin draw ratio λ _f increases. At the stage of uniaxial extension (pore formation) of annealed films, a particle ensemble transforms to spatial superlattices of lamellae. Numerical processing of electron microscopy images of the film surface show that the nonmonotonic dependences of the correlation length of density fluctuations and the ratios of the alternation period of particles along extension to their thickness on the parameter λ _f correspond to a unified mechanism of lamellae ordering.     

燃煤飞灰物理化学特性及其润湿机理研究

以小龙潭电厂燃煤飞灰及其不同粒径范围的分级灰为对象,采用X射线荧光光谱、X射线衍射、离子色谱、Zeta电位、扫描电镜等实验方法研究了飞灰的物理化学特征.同时采用沉降实验、表面张力实验研究了三种不同润湿剂对飞灰的润湿性能.研究发现,溶液对飞灰的润湿能力不仅取决于其气液界面张力,还与飞灰的组成、表面电位以及形貌特征密切相关.亲水性物质含量的增加,颗粒表面电荷与润湿剂分子间的静电吸引,颗粒表面的棱角孔隙等均可以促进其润湿;温度越高飞灰润湿性能越好,且温度对飞灰润湿过程影响较大,温度较高(60℃)时润湿剂种类及浓度对飞灰润湿过程的影响不明显.