Relative viscosity models and their application to capillary flow data of highly filled hard‐metal carbide powder compounds

The rheological behavior of highly filled polymer systems used in powder injection molding (PIM) technology strongly influences the final properties of the products. In this study, the capillary flow data of multi‐component polymer binders—based on polyethylene, paraffin, ethylene‐based copolymers, and polyethylene glycol—compounded with three various hard‐metal carbide powders were employed. The rheology of such highly filled (up to 50 vol%) multiphase systems is necessarily a complex phenomenon characterized by strain dependent, non‐Newtonian properties complicated by flow instabilities and yield. Over 15 mathematical models proposed for highly filled systems were tested, some of them calculating the maximum filler loading. Due to the complex structure of the filler (irregular shape, particle size distribution) and a multi‐component character of the binder, the applicability of these models varied with the powder‐binder systems studied. However, the particular values of maximum loadings are in good accordance with the predictions based on powder characteristics. Simple modification of Frankel‐Acrivos model to the systems containing unimodal hard‐metal carbide powders with particles of an irregular shape and broad particle size distribution gave precise agreement between experimental data and model prediction. POLYM. COMPOS., 26:29–36, 2005. © 2004 Society of Plastics Engineers.     

群体平衡方程在搅拌反应器模拟中的应用

群体平衡方程（population balance equation,PBE）是描述多相流体系中分散相大小与分布随时空变化的通用方程。搅拌反应器内多为多相流体系,考虑到颗粒聚并、破碎等微观机制对颗粒大小、分布、粒数密度等宏观参量的影响,采用PBE对搅拌槽内多相流体系进行数值模拟,可以较准确预测搅拌槽内流场和颗粒的大小与分布。对群体平衡方程在搅拌反应器数值模拟中的应用进行了综述,在简要介绍PBE的基本形式后,讨论了PBE的主要数值求解方法,然后着重介绍近年来采用PBE对搅拌槽内液固沉淀过程、气液及液液体系进行数值模拟的情况,并对今后的研究方向进行了展望。     

Optimal seed recipe design for crystal size distribution control for batch cooling crystallisation processes

The paper presents a novel quality-by-design framework for the design of optimal seed recipes for batch cooling crystallisation systems with the aim to produce a desired target crystal size distribution (CSD) of the product. The approach is based on a population balance model-based optimal control framework, which optimises the compositions of seed blends, based on seed fractions that result from standard sieve analysis. The population balance model is solved using a combined quadrature method of moments and method of characteristics (QMOM-MOCH) approach for the generic case of apparent size-dependent growth. Seed mixtures are represented as a sum of Gaussian distributions, where each Gaussian corresponds to the seed distribution in a particular sieve size range. The proposed methods are exemplified for the model system of potassium dichromate in water, for which the apparent size-dependent growth kinetic parameters have been identified from laboratory experiments. The paper also illustrates the simultaneous application of in situ process analytical tools, such as focused beam reflectance measurement (FBRM) for nucleation detection, attenuated total reflection (ATR) UV/Vis spectroscopy for concentration monitoring, as well as the in-line use of laser diffraction particle sizing for real-time CSD measurement.     

Synthesis and Investigation of Submicrometer Spherical Indium Oxide Particles

Spherical indium (In) oxide in submicrometer size is considered as a practical material in photonic bandgap applications. To obtain narrow size distribution, systematic studies of different conditions such as precursor concentration, reaction temperature, and other parameters have been carried out and are reported here. Tri- or dicarboxylic acid of citric acid (CA), malic acid, and tartaric acid were introduced into the reaction system and In-precipitates of spherical shape were produced. The particle size and internal morphology were observed by scanning electron microscopy and transmission electron microscopy. X-ray diffraction and thermal analysis were performed. The reaction kinetics analysis shows that the reaction rate depends on the reaction temperature, urea, and In concentration rather than on CA.     

Granular size and shape effect on electrostatics in pneumatic conveying systems

In solid processing systems, electrostatic problems are commonly observed for granules composed of various sizes and shapes. However, complete understanding about the functional dependence of electrostatic charge generation and transfer on the particle shape and size distributions has yet to be established. This observation has motivated the present study where novel methods are proposed to examine the effect of particle size and shape distributions on electrostatics. In this work, polyvinyl chloride (PVC) granule (original diameter 3.35-4.1 mm, in the shape of cylinders) was first discharged to remove any residual charges and subsequently its electrostatic charging was studied. Granular size and shape were varied by mechanical attrition conducted in a rotary valve jointly with a pneumatic conveying system. Characterised by induced current, particle charge density and equivalent current of the charged granular flow, granular electrostatics was found to increase with the extent of granular attrition in a continuous recycled pneumatic conveying process. In a separate setup, single particles (collected from the attrited granules formed in the rotary valve) were examined by correlating the extent of charge variation with size/shape. It was found that a dimensionless group, defined by the ratio of charge variation to size variation, is useful in describing the particle attrition process as this parameter increased with decreasing granule size. Smaller granules were found to be the main contributors in the enhancement of electrostatics charge density in bulk particles. By a separate shape analysis, it was uncovered that face shape requiring more shearing actions for its formation tended to give rise to a higher charge variation and so did column geometry. In this fashion, charge variation evaluated for whole attrited granules exhibited good agreement with the temporal variation of attrition weight; this applied for all air flow rates used in the conveying system. Furthermore, there is a reasonably good matching between results obtained by shape and size analyses.By the correlations presented above for single particle electrostatics either by size or shape analysis, charge variation of granular flow matched very well with that measured in the conveying system as well as the attrition process in the rotary valve. As such, the joint granule size and shape analysis has proven to be useful for characterisation of electrostatics in conveying systems where granules are made up of complex combinations of different particle sizes and shapes.     

Pattern recognition for characterization of pharmaceutical powders

A large part of pharmaceutical manufacturing involves the use of particulate materials. It is well known that both particle size and shape affect the physical characteristics of tablets. An image processing and analysis algorithm based on the invariant image moment technique was developed in this work to determine the particle shape by comparing features (moments) extracted from templates to those extracted from each of the objects in the image. First it determines the particle shape (rectangle, circle, etc.) and then calculates its specific dimensions (diameter, aspect ratio).The statistical validation of the vision system obtained a repeatability of 0.0012 in and 0.5% relative standard deviation and accuracy within 0.1 to 0.9% of the average value considered as true value. Also the pattern recognition technique indicated high precision and accuracy for images containing particles with some level of contact between them. The shape recognition of microcrystalline cellulose (MCC) indicated that particles of equant and acicular shape as defined by USP are predominant. The results suggest that image processing and analysis would be a suitable tool for pharmaceutical process analytical technologies (PAT) and process optimization.     

In situ particle size estimation for crystallization processes by multivariate image analysis

Crystal size estimation from in situ images has received attention recently as a means to estimate product properties in real-time. In this paper, an automated image analysis strategy that combines classical image analysis techniques with multivariate statistics has been developed for online analysis of in situ images from crystallization process. The strategy introduces a novel image segmentation step based on information extracted from multivariate statistical models. Experimental results for batch cooling crystallization of monosodium glutamate show that the strategy effectively extracts crystal size and shape information from in situ images. The robustness and efficiency of the method has been established by comparing its performance with those obtained by manual analysis of the images. The method yields reasonably good estimates of particle length and is also fast enough to provide online measurements for the purpose of online optimization and control of a typical crystallization process.     

Measurement of size and shape distributions of particles through image analysis

The size and shape of particles can be described using a 2D particle size distribution (PSD) where two characteristic lengths define each particle in the population. The determination of 2D PSDs based on microscopic pictures of particles in suspension is studied. The experimental data are represented as an axis length distribution (ALD) that can be extracted from a series of microscopic pictures by a fully automated image analysis. The problem of finding the underlying bi-dimensional PSD is stated as an optimization problem. For the solution a genetic algorithm is used. The approach is tested on simulated ALDs, as well as on an experimentally measured ALD obtained from carbon fiber particles.     

Effect of Particle Shape on Anisotropic Packing and Shrinkage Behavior of Tape-Cast Glass–Ceramic Composites

In this study, the influence of particle shape anisometry and particle alignment in tape-cast green sheets on the shrinkage behavior of low-temperature co-fired ceramics (LTCCs) was investigated quantitatively. A new method for the characterization of particle shape with the use of a particle image analyzer is presented, and its application to real material systems demonstrated. A commercial LTCC system and three developed composite powders with different average particle sizes were analyzed. After tape casting, particle alignment in the green sheets was analyzed using image analysis of SEM micrographs of cross sections. The investigations showed that the degree of particle alignment correlates significantly with the particle shape and size of the materials. A further increase in particle orientation was seen after the lamination process. Additionally, the powder packing of both single layers and laminates was analyzed by mercury porosity. The anisotropic shrinkage behavior during the sintering process was determined by means of optical dilatometry. The data obtained on the particle morphology, particle orientation in the tapes, and their effects on the shrinkage anisotropy will be discussed.     

An improved estimation of size distribution from particle profile measurements

Several methods are available to measure particle size. The majority of them, such as sieving, are off-stream techniques where samples must first be separated from the main stream for analysis.Therefore, the search for on-line particle size analysis systems has provided the impetus for the introduction of image-based particle size analysers to the mineral industry in the past three decades. Generally, the estimation of particle size distribution on the basis of image analysis depends on measuring a single parameter of particle profile. For example the equivalent area diameter (d_A) or mean Feret's diameter (d_F) distributions, then transforming this data to the equivalent size distribution. However, due to the irregularity of particles being analysed, it is believed that this kind of analysis may increase the error in estimation of particle size distribution since profiles of irregular particles carry more information than can be represented by a single parameter.In this paper, a proposed technique which measures two parameters, equivalent area diameter (d_A) and mean Feret's diameter (d_F), for each particle profile has been developed. The accuracy of the technique has then been investigated in the laboratory by successfully estimating (unfolding) the size distribution, where size refers to sieve size, of three samples of different particle shapes with known size distribution.     

Modeling of Mixing and Reaction in Turbulent Multi‐Phase Flows with Distribution Functions

Numerical simulation of turbulent reacting or multiphase flows is gaining popularity as a tool for the analysis and optimization of many complex applications in process engineering. To make possible the accurate modeling of relevant reaction and transport processes, the respective distribution functions of mixture fraction or particle size must be considered in an adequate manner. In the present paper, novel approaches to make possible a more detailed yet efficient representation of distribution functions in turbulent, reacting multiphase flows are introduced. The application of the methods to the example of a system with mixing and reaction among three species is discussed.     

高压静电抗溶剂法制备聚乳酸微球

以无水乙醇为非溶剂,采用高压静电抗溶剂法制备聚乳酸微球。通过24全因子试验设计对微球粒径和粒径分布的影响因素进行了显著性分析。并考察最显著因素对微球表面形貌的影响规律。结果表明,推进速度是影响微球粒径的最显著因素,最优条件下微球表面光滑、球形度好,粒径分布窄。浓度为3%,相对分子质量为5万～10万的聚乳酸制备的微球,球形度较好。经过高压静电处理后,傅里叶红外光谱测定表明聚乳酸无明显结构摄动;X射线粉末衍射分析表明聚乳酸晶体结构未发生明显变化。     

Challenges in particle size distribution measurement past, present and for the 21st century

The field of particle size distribution (PSD) characterization and measurement has experienced a renaissance over the past ten years. This revitalization has been driven by advances in electronics, computer technology and sensor technology in conjunction with the market pull for PSD methods embodied in cost effective user friendly instrumentation. The renaissance can be characterized by at least four activities. (1) End user innovation exemplified by techniques such as hydrodynamic chromatography (HDC), capillary hydrodynamic fractionation (CHDF) and field flow fractionation methods (SdFFF, FlFFF, and ThFFF). (2) Revitalization of older instrumental methods such as gravitational and centrifugal sedimentation; (3) Evolution of research grade instrumentation into low cost, routine, user friendly instrumentation exemplified by dynamic light scattering (DLS). (4) The attempt to meet extremely difficult technical challenges such as: (a) providing a single hybrid instrument with high resolution over a very broad dynamic range (4+ decades in size; e.g., Fraunhofer/Mie; photozone sensing/DLS); (b) PSD measurement of concentrated dispersions (acoustophoretic, dielectric measurements, fiber optic DLS (FOQELS)); (c) in-situ process particle size sensors (in-line or at line, e.g., FOQELS); (d) routine measurement of particle shape and structure (e.g., image analysis). Instrumental methods resulting from these activities are discussed in terms of measurement principles and the strengths and weaknesses of these methods for characterizing PSDs. Business and societal driving forces will impact customer perceived instrumentation and knowledge needs for the 21st century and the ability to meet the specific difficult technical challenges in particle size distribution characterization mentioned above. Anticipated progress toward meeting these technical challenges is discussed in conjunction with the associated anticipated advances in required technologies.     

Size and shape characterization of conventionally and cryogenically ground turmeric (Curcuma domestica) particles

Turmeric (Curcuma domestica) powder was produced by conventional grinding and cryogenic grinding processes. The particle size and shape analyses of the ground particles were carried out, utilizing the measurement system based on time-of-transition (TOT) principle. Weight mean diameter of cryo-ground particles are 50-μm finer than conventional-ground turmeric. The size distribution in both grinding methods followed the well known Rosin–Rammler–Bennett (RRB) equation. The shape parameters of the particles of both grinding processes such as perimeter, shape factor (sphericity), average Ferret diameter, aspect ratio were measured. The shape parameters of cryo-ground turmeric were in the lower range than those of conventionally ground turmeric. The analysis confirms the usefulness of cryo-ground process in producing finer particles for heat-sensitive materials such as turmeric.     

In‐Line Monitoring of Crystallization Processes Using a Laser Reflection Sensor and a Neural Network Model

Laboratory‐scale experiments were carried out for measuring the chord length distribution of different particle systems using a laser reflection sensor. Samples consisted of monodisperse, polydisperse and bimodal FCC catalyst and PVC particles of different sizes, ranging from about 20 to 500 μm. The particles were dispersed in water, forming suspensions with solid‐phase mass fractions ranging from ca. 0.2 % until ca. 30 %. The experimental results, consisting of the particle number counting per chord length class, were used in fitting a neural network model for estimating the mass concentration of particles in the suspension and the volume‐based size distribution, eliminating the effects of suspension concentration and particle shape. The results indicate the feasibility of using such a model as a software sensor in crystallization processes monitoring.     

Analysis of polymer blend morphologies from transmission electron micrographs

Thermomechanical properties of polymer blends seem to depend on their morphology on microscales and in particular on the size of the dispersed phase particles and/or their distances (ligament thickness). Precise characterization of morphologies by few simple geometrical parameters is often a quite delicate task, in particular because of the strong polydispersity of these systems. We present here a simple method based on image analysis of transmission electron micrographs (TEM) to estimate both distributions in particle size and ligament thickness. We first reconstruct three-dimensional distributions in particle size from two-dimensional measurements and show in particular that corrections from section thickness become significant when thickness is comparable to particle size. Knowing the distribution in particle size, we extend the model initially proposed by Wu to estimate the distribution in ligament thickness. This method provides a more detailed relation between the distribution in particle size and the distribution in ligament thickness. Advantages and limitations of the method are illustrated by practical examples on polyamide-12 systems filled with various particle dispersions.