微观图像技术在超细材料粒度分析中的应用

应用计算机微观图像采集分析系统建立了一套对超细材料进行形状表征和粒度测量的方法。该方法克服以往图像法测量样本小 ,得不到正确粒度分布的弊端。通过对SiO2 标准物的粒度测定表明 :均匀、单分散的测量样片的制备是图像法准确测量和分析的关键。当测量图片在 6张以上 ,累积测量颗粒总数在 2 0 0个左右时 ,测量结果具有代表性。该系统用于测量的粒度范围为 0 .5 μm～ 1cm的粒子时 ,长度测量误差小于 5 % ,颗粒等面积直径测量偏差小于12 %。     

Light scattering from nonspherical airborne particles: experimental and theoretical comparisons

A laser light-scattering instrument has been designed to permit an investigation of the spatial intensity distribution of light scattered by individual airborne particles constrained within a laminar flow, with a view to providing a means of classifying the particles in terms of their shape and size. Ultimately, a means of detecting small concentrations of potentially hazardous particles, such as asbestos fiber, is sought. The instrument captures data relating to the spatial distribution of light scattered from individual particles in flow. As part of an investigation to optimize orientation control over particles within the sample airstream, the instrument has been challenged with nonspherical particles of defined shape and size, and a simple theoretical treatment based on the Rayleigh-Gans formalism has been used to model the spatial intensity distribution of light scattered from these particle types and hence derive particle orientation data. Both experimental and theoretical scattering data arepresented, showing good agreement for all particle types examined.     

基于分形理论的磨粒图像定量分析

探讨了分形理论在磨粒图像处理中的应用。首次将Sierpinski分形维数张磨粒图像的定量分析。对试验所获得的磨粒图像的Sierpinski分形维数分析发现：磨粒图像Sierpinski分形维数的大小与磨粒尺寸分布和磨粒重叠程度有关。磨粒图像的Sierpinski分形维数可以实现磨粒图像的特征提取。     

Effect of kneading process conditions on the particle fineness and the polydispersity in nanocomposites

This paper is part of a series of publications that cover the entire process chain to produce nanocomposites. The associated papers are published in the chronological sequence and broach the issues of: “production and dispersing of nanoparticles”, “characterisation of the liquid and reactive matrix” as well as “resulting composite properties by experimental and simulation methods”. Nevertheless, all resulting composite properties are strongly dependent on the method of particle incorporation and on the particle size distribution. Therefore, this study focuses on the optimisation of the dispersion referring to finest particles, smallest particle size distribution, shortest dispersing time and lowest specific energy. In order to prepare the matrix suspension, nano-fillers were dispersed conducting shear mixing techniques in a high performance laboratory kneader. As carrier fluid epoxy resin and a corresponding anhydride hardener system were chosen. Tests were performed using neat and surface modified alumina particles at different levels of particle concentrations. The particle size distribution was determined using dynamic light scattering directly after the dispersing process. Additionally each sample was characterised after 1, 3 and 7 days. Since similar examinations were performed for all formulations, a statement on the influence of re-agglomeration processes and the role of surface modification can be derived. By correlating the progress of the dispersing process to the mass fraction and the particle size distribution, the dispersion process can be evaluated regarding the dispersing time, specific energy and product quality. However, an optimum polydispersity can be found between 25 and 30 wt.%, even if the finest average particle size is reached at higher mass fractions around 45 wt.%. Silane modified alumina particles in epoxy resin constitute the most stable system against re-agglomeration, although the finest particles and the smallest specific energy are attained in non-modified systems. Moreover it can be concluded, that resulting properties of the cured composite are strongly related to the aspired optimisation, e.g. product fines, particle size distribution, required energy input and stability.     

Image vector histogram approach to nanoparticle sizing

A novel approach to measuring the size distribution of particles in the range of a few nanometers to a few micrometers is described. The method is based on processing multiple images of a sample of particles suspended in a liquid and undergoing Brownian motion. From each image, the centers of the particle positions are measured, then a histogram of the vectors connecting the centers in each image with all the centers in the next image is formed. This vector histogram contains information about the particle size distribution. A maximum-likelihood data inversion procedure to invert the data to yield a particle size distribution is described. Both computer simulation and experimental results are presented to demonstrate the effectiveness of the approach.     

Multi-sensor inline measurements of crystal size and shape distributions during high shear wet milling of crystal slurries

Size and shape distributions are among critical quality attributes of particulate products and their inline measurement is crucial for monitoring and control of particle manufacturing processes. This requires advanced tools that can estimate particle size and shape distributions from multi-sensor data captured in situ across various processing steps.In this work, we study changes in size and shape distributions, as well as number of particles during high shear wet milling, which is increasingly being employed for size reduction in crystalline slurries in pharmaceutical processing. Saturated suspensions of benzoic acid, paracetamol and metformin hydrochloride were used in this study. We employ our recently developed tools for estimating particle aspect ratio and particle size distributions from chord length distribution (CLD) measurements and imaging. We also compare estimated particle size distributions from CLD and imaging with corresponding estimates from offline instruments.The results show that these tools are capable of quantitatively capturing changes in particle sizes and shape during wet milling inline. This is the first time that such a capability has been reported in the literature. The ability to quantitatively monitor particle size and shape distributions in real time will enable development of more realistic and accurate population balance models of wet milling and crystallisation, and aid more efficient control of crystallisation processes.     

数字成像颗粒分析仪在聚丙烯粉料测试中的应用

为了考察CAMSIZER数字成像颗粒分析仪用于聚丙烯粉料测试的可行性,采用CAMSIZER数字成像颗粒分析仪对聚丙烯粉料样品的粒度分布进行了测试,考察了测试结果的重复性,并对该仪器在粒度分布测试同时获得颗粒球形度数据和颗粒照片的功能进行了验证。结果表明:粒度分布测试自动化程度高,测试速度快,结果重复性好,与筛分法比较,工作量大大降低;在进行粒度分布测试的同时,可获得颗粒的球形度数据和颗粒投影照片。     

A new method to determine specific surface area and shape coefficient of a cohesionless granular medium

The specific surface area of soil grains (SSA) influences the physical and chemical properties of soil. Despite the widespread application of the SSA, it is often determined by analytical equations or estimated using empirical relationships and visual comparisons. On the other hand, little attention has been paid, especially to three-dimensional and precise measurements. In this study, the precise SSA and shape coefficient was measured in a group of aggregate with different sizes and shapes using a novel method. Geometrical properties such as volume and surface area were measured for each particle using X-ray micro-computed tomography (µCT) images and image processing. The particle shape coefficient was obtained from the specific surface area and effective diameter. Further, the particle shapes were measured in three distinct characteristics, sphericity, roundness, and roughness. Particle's roundness was measured by Wadell’s formula in the plan outline, which did not show an agreement with the shape coefficient. Nevertheless, as the particle sphericity decreases and roughness increases, the shape coefficient is increased. Hence, the shape coefficient of grains was classified based on the sphericity and the surface roughness. The measured SSA and shape coefficient, for 12 gradations with the three different particle size distribution and four different particle shapes, indicated good agreement with predictive analytical relations for rounded and crushed grains and more dissimilarity for flaky and elongated grains. This novel method can provide the quantitative/qualitative classification for non-spherical particles and also improve our understanding on the properties of granular media.     

Systematic study of bimodal suspensions of latex nanoparticles using dynamic light scattering

Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (DLS). In principle, DLS is able to estimate the hydrodynamic particle diameter and its intensity-weighted distribution. However, the measured correlation function or power spectrum must be inverted to obtain this size distribution. The inversion is an ill-posed mathematical problem, and only under certain assumptions can the distribution be determined reliably. Suspensions containing bimodal (or multi-modal) particle size distributions are particularly challenging. This study reports on DLS measurements on a range of bimodal distributions of latex spheres with varying ratios of particle sizes. To determine the efficacy of different inversion techniques, the data has been analyzed both with the algorithms implemented in the DLS instrument’s proprietary analysis software and with other inversion routines based on simple analytical models of the particle size distribution. In addition, the results of the DLS analysis have been compared to scanning and transmission electron microscopy (SEM and TEM) measurements.     

Synthesis, characterization, UV and dielectric properties of hexagonal disklike ZnO particles embedded in polyimides

A series of novel ZnO/polyimide composite films with different ZnO contents was prepared through incorporation hexagonal disklike ZnO particles into poly(amic acid) of the pre polymer of the polyimide. The hexagonal disklike ZnO particles with a diameter of 300-500 nm were synthesized from zinc acetate and NaOH in water with citric acid. The prepared zinc oxide-polyimide composites were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction and thermal analysis techniques. Thermal analyses show that the ZnO particles were successfully incorporated into the polymer matrix and these ZnO/polymer composites have a good thermal stability. Scanning electron microscopy studies indicate the ZnO particles were uniformly dispersed in the polymer and they remained at the original size (300-500 nm) before immobilization. All composite films with ZnO particle contents from 1 to 5 wt% show good transparency in the visible region and luminescent properties.     

Determination of particle size distributions and the degree of dispersion in nanocomposites

Objective of this study was the investigation of measurement techniques to determine the quality of the dispersion process of nanoparticles in polymer composites. In order to prepare the matrix suspension, alumina nanoparticles were dispersed applying shear mixing techniques in a high performance laboratory kneader. The product quality in liquid state was determined by means of dynamic light scattering (DLS) and centrifugal sedimentation analysis (CSA). However, particle measurements in carrier fluids like epoxy resin are complex and challenging. Measuring values like particle size distribution and grade of homogeneousness are strongly influenced by the sample preparation and adjustments of the measuring device. Within this study the machine settings and the formulation was analysed systematically. Hereby an identification of the key parameters and an optimisation of the measuring process were possible. Additionally, the composite was cured and analysed by scanning electron microscopy (SEM). Finally all measuring techniques were evaluated and compared among each other. Thus, DLS is the fastest method to measure spherically particles in the liquid matrix, CSA allows a certain deviation from the spherical shape and SEM gives a qualitative impression of the final particle size in cured composite condition.     

Simultaneous shape and size measurements of irregular rough particles by an IPI system with double receivers

This paper proposes a method of obtaining the shape and the size of irregular rough particles, which are abundant in particle fields. The approach uses the infocused image of the particle to determine its size, and an improved relation between the central peak of the 2D-autocorrelation of its defocused image and its size to obtain the shape. An interferometric particle imaging system with double receivers is established to simultaneously collect the infocused image and defocused image. Experiments confirm the effectiveness of the proposed algorithm with a measurement relative error on the sample particles not exceeding 10.4%. In general, this method can offer significant perspectives on the characterization of particle fields.     

Comparison of Particle Size Distributions Measured Using Different Techniques

In this article, particle size distributions (PSDs) measured by different techniques, including image analysis (IA), laser diffraction (LD), ultrasonic attenuation spectroscopy (UAS), and focused-beam reflectance measurement (FBRM), are compared for spherical glass beads and nonspherical silica flakes. It is shown that particle shape strongly affects the results obtained by different techniques. For spheres, the PSDs obtained by IA, LD, and UAS agree well. There is no consistent result among different particle measurement techniques for nonspherical particles. The conversion between PSDs obtained by IA, LD, and UAS has been based on particle shape factors. Caution must be exercised when a measured chord length distribution (CLD) is used to indicate the PSD during a process because the CLD result obtained by FBRM is complex, depending not only on the PSD, but also on particle optical properties and shape.     

Microencapsulation by a Solvent-Free Supercritical Fluid Process: Use of Density, Calorimetric, and Size Analysis to Quantify and Qualify the Coating

Coating of microparticles or microencapsulation is a widely used operation in which a thin layer of a coating agent is deposited onto a solid particle. Currently, the technique faces two challenges: being solvent-free and being applicable for coating particles smaller than 80 microns. In this work, several techniques are used to test the feasibility of a new solvent-free coating process using supercritical fluid technology. Some model microparticles, glass beads, and an active compound (AC) are coated with Precirol®, which is a mixture of fats. The process involves two steps: first supercritical CO₂ is dissolved in molten Precirol®, then the melt solution is sprayed onto the host particles by a rapid expansion. The particles coated in this way are examined by particle size analysis, environmental scanning electron microscopy (ESEM), and IR spectrophotometry. Also mass ratios of host particle to coating are evaluated using both helium pycnometry to determine sample density and calorimetry to measure the heat of fusion of the coating agent. The results show that these analytical techniques can be used for qualitative analysis as well as quantification of the coating. Thus they give relevant information on reproducibility and feasibility of the new process.     

SEPARATION AND BEHAVIOR OF NONSPHERICAL PARTICLES IN SEDIMENTATION/STERIC FIELD-FLOW FRACTIONATION

Sedimentation/steric field-flow fractionation (Sd/StFFF) is an elution separation technique capable of measuring the size distribution of 0.3-100 µm spherical and near-spherical particles with advantages including high resolution, fast analysis, and the ready collection of narrow size fractions. In this study we investigate the applicability of Sd/StFFF to various nonspherical particles including the doublets of spheres, rod-shaped glass fibers, compressed latex discs, and quartz particles (BCR 67 and 70) with complex mixed shapes. Some fractionation, retention, and selectivity features of these particles are defined and measured in relationship to those of spheres (latex beads), which are better understood. While the relative behavior of these two particle types depends on many factors, especially the distance of the particle from the Sd/StFFF channel wall, in most cases the nonspherical particles are eluted before spheres of equal volume and they often display higher selectivity than spherical particles. However, when retention of nonspherical particles is compared with that for spheres whose diameter is equal to the particle length, elongated particles (doublets and rods) eluted after the sphere while flattened particles (discs) eluted earlier than spheres, an observation that might assist in shape discrimination by Sd/StFFF. Thus, when latex microspheres are used for calibration to obtain size distribution curves, the diameter obtained for any given subpopulation will be less than the length of rods but greater than the diameter of discs. For complex particles such as the quartz particles, the diameter of a particle provided by classical sedimentation using spherical calibration is less than the equivalent spherical diameter of the particle in question whereas Sd/StFFF yields a diameter somewhat greater than the particle length. Thus, these two techniques will yield size distribution curves displaced from one another along the diameter axis. The difference in diameters can be eliminated by using a diameter correction factor of 2.7, which brings the distribution curves for quartz obtained by these two techniques into concurrence.     

Size and distribution: a comparison of XRD, SAXS and SANS study of II-VI semiconductor nanocrystals

The uniqueness of size dependent functional properties of II-VI semiconductor nanocrystals have led to the development of various techniques for determination of shape, size and distributions, although the accurate measurements of the particle sizes has always been a fundamental task in nanoscience and even become more crucial with the discovery of quantum confinement effect. A comparison of the well established techniques X-ray diffraction (XRD), small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) with an emphasis on size and distribution of the prepared samples are reported in order to elaborate more precise techniques for the analysis of particles sizes. Modified Scherrer formula for spherical particles has been used to calculate the particle sizes from XRD spectra. Analysis of SAXS data has been reported using Guinier model. Small angle neutron scattering measurements has been performed for ZnO nanocrystals and the scattering data obtained is simulated for polydisperse sphere. The bare ZnO, ZnS and CdS and doped with Mn2+ systems are taken within the framework of our discussion. These materials were synthesized by chemical precipitation route and found to have size distribution from 2 to 6 nm for spherical particles. Sizes determined from various techniques are in good agreement with each other however small angle scattering technique is more reliable than XRD to determine the sizes of the nanoparticles.     

Comparison of Particle Size Distributions Measured Using Different Techniques

ABSTRACT

In this article, particle size distributions (PSDs) measured by different techniques, including image analysis (IA), laser diffraction (LD), ultrasonic attenuation spectroscopy (UAS), and focused-beam reflectance measurement (FBRM), are compared for spherical glass beads and nonspherical silica flakes. It is shown that particle shape strongly affects the results obtained by different techniques. For spheres, the PSDs obtained by IA, LD, and UAS agree well. There is no consistent result among different particle measurement techniques for nonspherical particles. The conversion between PSDs obtained by IA, LD, and UAS has been based on particle shape factors. Caution must be exercised when a measured chord length distribution (CLD) is used to indicate the PSD during a process because the CLD result obtained by FBRM is complex, depending not only on the PSD, but also on particle optical properties and shape.     

透射电镜图像分析法测定丁苯胶乳的平均粒径及其粒径分布

丁苯胶乳(SBL)经稀释、超声分散、四氧化锇(OsO_4)染色后,利用透射电镜(TEM)获取其图像,采用图像分析仪阴影矫正、编辑图像、颗粒分割等功能对获取的图像进行处理,通过粒子个数百分比的直方图表示其粒径分布,建立了丁苯胶乳平均粒径及其粒径分布的测定方法。结果表明:该方法的相对标准偏差为2.8%,相对误差为7%,因而其准确性及重复性都较好。     

Transformation of Chord Length Distributions into Particle Size Distributions Using Least Squares Techniques

For the characterization of particulate systems, various measuring techniques exist. Many of these assume that the particles are spherical in order to compute a particle size distribution (PSD) from the measured data. However, in many applications the shape of the particles deviates from a sphere, and as a consequence the computed PSD will contain errors because of this violated assumption. Measuring techniques that do not require this a priori assumption are, for example, those that measure the chord lengths of the particles. A disadvantage of the latter techniques is that the interpretation of the chord length distribution (CLD) is less transparent than the interpretation of a shape-based PSD (the PSD given an assumed particle shape). To facilitate the interpretation of a CLD, an algorithm based on least squares optimization techniques is presented. This algorithm computes the shape-based PSD that best explains the measured CLD and can, for example, discriminate spheres from rods using information of the CLD only. Knowledge about the type of PSD (e.g., Gaussian or log-normal) is not required.