Specific Features in Measuring Particle Size Distributions in Highly Disperse Aerosol Systems

The distribution of highly dispersed aerosols is studied. Particular attention is given to the diffusion dynamic approach, as it is the best way to determine particle size distribution. It shown that the problem can be divided into two steps: directly measuring particle penetration through diffusion batteries and solving the inverse problem (obtaining a size distribution from the measured penetrations). No reliable way of solving the so-called inverse problem is found, but it can be done by introducing a parametrized size distribution (i.e., a gamma distribution). The integral equation is therefore reduced to a system of nonlinear equations that can be solved by elementary mathematical means. Further development of the method requires an increase in sensitivity (i.e., measuring the dimensions of molecular clusters with radioactive sources, along with the activity of diffusion battery screens).     

凝并和成核机理下颗粒尺度分布的Monte Carlo求解

颗粒的凝并和成核现象影响其尺度分布,现有的MonteCarlo方法描述颗粒尺度分布的时间演变过程存在若干困难.提出了一种新的多重MonteCarlo(MMC)算法,基于时间驱动,利用加权的虚拟颗粒的思想,在模拟过程中保持虚拟颗粒总数不变和计算区域体积不变.利用该算法对“常凝并核,一阶成核”的情况下颗粒尺度分布的时间演变过程进行了数值求解,所得结果与数值解相符,表明MMC算法具有高且稳定的计算精度.另外,MMC算法由于跟踪比实际颗粒数目少得多的虚拟颗粒而具有较低的计算代价.     

Genetic Algorithm Approach to the Determination of Particle Size Distributions from Static Light-Scattering Data

The application of genetic algorithms to the inversion of static light-scattering (SLS) measurements is investigated. The approach is illustrated using simulated data on samples with unimodal, bimodal, and trimodal distributions of spherical particles. Particles having diameters in the range from 100 to 4000 nm are treated. Results are compared with other inversion procedures. It is found that genetic algorithms yield very good results in this situation.     

Measurement of Continuous Particle Size Distributions of Finely Dispersed Powders by the Dynamic Light Scattering

Dispersity of finely dispersed powders with continuous bell-shaped particle size distributions is measured. The measurements are performed using two different dynamic light scattering instruments, a transmission electron microscope, and a sedimentograph equipped with an X-ray detector. Correlation functions measured with the dynamic light scattering instruments are processed using the CONTIN and KLUB software packages. Comparative analysis of the results obtained by different methods demonstrated that a reliable information on the dispersity of samples with wide particle size distributions can be obtained but using a combination of several analytical methods.     

A Simple Method of Evaluating Particle Size Distributions and Settling Rates for Silica Based Chromatographic Supports

Abstract

A simple and inexpensive method of evaluating particle settling rates and the particle size distribution of chromatographic supports using common laboratory equipment is reported. The time dependence of the turbidity of a solution of silica support particles suspended in an appropriate liquid is measured on a spectrometer. Digital acquisition allows data manipulation using simple algorithms to yield the distribution of particle sizes based on the Stoke's diameter. This data can easily be transformed into the most useful form for presentation, e.g. number average, weight average, cumulative distribution, etc.     

粒度分析及粒度标准物质研究进展

综述了当前粒度分析测试方法的研究进展,并简单介绍了各种测试方法的基本原理以及包括美国、欧洲、中国在内的国家和地区在粒度标准物质方面的研究概况。     

Simultaneous Voltammetric Determination of Zn,Cd and Pb at Bismuth Nanopowder Electrodes with Various Particle Size Distributions

Effect of particle size distribution on sensor characteristics of nano‐Bi fixed electrode has been investigated using square wave anodic stripping voltammetry. Bi nanopowders with various particle size distributions were synthesized by gas condensation (GC) method with the change of chamber pressure. As the chamber pressure decreased, the size of Bi nanopowder became smaller with narrower distribution due to a shorter residence time of Bi vapor. The square wave anodic stripping voltammograms (SWASV) showed well‐defined and highly reproducible peaks at ?1.2 V, ?0.8 V and ?0.6 V (vs. SCE), which are closely related to the oxidation of Zn, Cd and Pb, respectively. The sensitivity and detection limit of the nano‐Bi fixed electrode were quantitatively estimated from the analyses of SWASV. From the results, it is concluded that as the size of Bi nanopowder becomes smaller with narrower particle size distribution, the sensitivity and detection limit of sensor electrode for Zn, Cd and Pb are improved, which is ascribed to the increase in electrochemical‐active surface area.     

Aerodynamic Time-of-Flight Particle Size Measurement

ABSTRACT

The principles of aerodynamic time-of-flight particle size characterization are reviewed, and the associated mechanics are illustrated for a commercially available instrument system. Examples are illustrated for pharmaceutical and titania samples. Future applications for time-of-flight measurements in combination with other measurement techniques are discussed.     

超细钛硅分子筛粒径的激光粒度分析

研究了试样浓度、超声波强度、分散时间及分散剂的加入对钛硅分子筛粒度测定结果的影响，结果表明，试样浓度低或高，粒度测定结果偏大；超声波强度的增大和超声波分散时间适当的延长有利于粒子的分散，也有利于粒度的准确测定；加入分散剂六偏磷酸钠后，测试结果重复性好。     

Study of Bimodal Drop Size Distributions of Emulsion

In order to increase the present understanding of bimodal emulsion drop size distributions, systematic series of experiments have been carried out to investigate the effects of formulation variables on bimodal drop size distributions, and probability distribution functions were proposed to analyze the distribution. The results show that, the span of the drop size and Sauter mean diameter become larger when the dispersed phase volume fraction becomes higher and rotor speed becomes lower; the Frechet function represents the experimental data satisfactorily. The prediction model of Sauter mean diameter established by combining the prediction theory of the maximum stable drop diameter and experimental analysis results can fit the experimental data well.     

铝酸钠溶液附聚过程中的粒度信息分析

实验研究了76℃条件下,Na2Ok=140g l-1,αk=1.37的铝酸钠溶液种分附聚过程.通过附聚过程中的粒度信息分析发现:附聚首先发生在0-10 μ m的小粒子之间,然后才是较大粒径的粒子;一定粒径的粒子发生附聚时,其体积分数分布随时间的变化呈现波峰与波谷相间的规律,波峰与波谷出现的时间基本上是相同的,但随着粒径的增加,波峰、波谷的出现时间略有后移.由此可望进一步计算动力学参数.     

Matrix Representation of Polymer Chain Size Distributions, 2

Analysis of the mass balance equations that describe a reaction system may be useful to provide information about its dynamics, such as the restricted set of compositions that can be achieved from a given set of initial compositions and the effect of feeding reactants to the reaction environment along the reaction course. Since these results may be important for the formulation of reaction policies, this work presents the properties of a matrix polymerization model previously developed and extended to describe transient conditions. This model is based on the definitions of two matrices: the consumption matrix ( A − Kt ), which contains information about chemical transformations among the many active polymer species in the system, and the propagation matrix Kp , which contains information about chain growth. It is shown that the set of mass balance equations that describes the dynamics of active chemical species in polymerization reactions has a stable and unique solution, which is bounded if feed rates are also bounded. It is also shown that the set of compositions that may be reached through manipulation of the feed rates is restricted and may not include all possible chemical compositions. Finally, it is shown that the obtained molecular weight distributions are special multiple time convolutions of the initiation rates.

     

细粒度氧化钇生产的新方法

采用氨水与氯化钇溶液共沉淀制得Y(OH)3胶体, 再加草酸溶液转化, 可制得细粒度Y2O3粉末(D50=1～2 μm). 初步探讨了制备工艺中的有关因素, 在选定条件下, 沉淀过程物料浓度、温度、加入速度对最终产物D50有一定影响, 但不明显. 草酸沉淀母液最终pH值对D50影响最大.     

Transient Processes in the Disperse System with Coagulation and Aggregate Disintegration

The kinetics of transition of the coagulating disperse system with aggregate disintegration into a new equilibrium state was considered in the course of the disturbance of the earlier existing equilibrium, which is caused by a change in the flow shear rate. An analysis carried out on the basis of a two-fraction model of dispersed phase [B.M. Dolgonosov, Kolloid. Zh., 2001, vol. 63, no. 1, p. 32] has shown that the spectrum of fine-fraction particles is a superposition of the initial and final states with the superposition coefficients dependent on the current value of the average mass of coarse-fraction particles (large-size aggregates). The spectrum of large aggregates in the form of a quasi-equilibrium distribution of a Gaussian type with time-dependent parameters was obtained. The variation of superposition coefficients and parameters of the spectrum of large aggregates with time was calculated. The conditions of applicability of the suggested approach were discussed.     

Maximum Achievable Particle Size in Emulsion Polymerization: Modeling of Large Particle Sizes

A simplified model for particle formation in emulsion polymerization (comprising aqueous‐phase propagation to degrees of polymerization which may enter a pre‐existing particle and/or form new particles by homogeneous or micellar nucleation, coupled with the aqueous‐phase and intra‐particle kinetics of oligomeric radicals) is formulated to provide a model suitable for the simulation of systems containing large‐sized particles. The model is particularly useful to explore conditions for growth of large particles while avoiding secondary particle formation. Applied to the Interval II emulsion polymerization of styrene with persulfate initiator at 50°C, it is found that there is an effective maximum particle size that can be achieved if the formation of new particles is to be avoided. The parameter space of initiator concentration, particle number concentration and particle radius is mapped to show a “catastrophe” surface at the onset of new nucleation. Advanced visualization techniques are used to interpret the large number of simulations in the series, showing a maximum achievable particle diameter of around 5 μm.     

超细稀土氧化物粉体粒度测定

采用美国布鲁克海文仪器公司制造的90 Plus粒度仪测定超细稀土氧化物粉体粒度. 以氧化钇为研究对象, 研究了分散剂、悬浮介质、待测样品浓度、分散时间等因素对亚微米级氧化钇粉体粒度测量精度的影响. 由此确定了能准确测定亚微米级氧化钇粉体粒度的测量条件.     

SAPO-11分子筛的粒度调控

采用干凝胶法,通过向合成体系中添加适量的十六烷基三甲基溴化铵(CTAB)或氟化氢(HF)控制SAPO-11分子筛的粒度。采用SEM、XRD、IR、MAS NMR、TPD、TEM、TG-DSC以及低温N2吸附脱附对产物进行表征。结果表明,CTAB或HF的加入不仅能够减小分子筛的粒度,而且能调控分子筛骨架元素组成、表观形貌、孔道结构及酸性质等。其中,CTAB的加入有利于Si进入分子筛骨架,增加产物的酸量;HF的加入使样品由不规则的微米级颗粒调控为500 nm左右的棒状单晶,增强了分子筛的稳定性,但阻止了硅进入骨架,降低产物的酸量。     

Particle Size Limit for Concomitant Tuning of Size and Shape of Platinum Nanoparticles

Based on a polyol process, one-step synthetic procedures were investigated for concomitant control of the shape and size of platinum nanoparticles (Pt NPs). Cubic and octahedral/tetrahedral particles of different sizes (5–10 nm) were synthesized using these procedures. Further attempts to control the shape of the NPs below 3–4 nm failed. It was found that 3–4 nm is the particle size limit for Pt NPs above which the particle size and shape can be concomitantly controlled.     

Rheological Properties and Orientational Distributions of Dilute Ferromagnetic Spherocylinder Particle Dispersions

We have investigated the rheological properties and the orientational distributions of particles of a dilute colloidal dispersion, which is composed of ferromagnetic spherocylinder particles, subject to a simple shear flow. The governing equation of an orientational distribution function has been derived from the balance of the torques acting on a particle in an applied magnetic field. After a spherical harmonic expansion, an approximate solution to the governing equation has been found by Galerkin's method. The results obtained are summarized as follows. The orientational distribution function has a sharper peak for a stronger magnetic field, and the position of the peak changes from the flow direction to the magnetic field direction as the magnetic field comes to govern the shear flow. Since the orientation of the particle is highly restricted in the field direction as the magnetic field becomes strong, the viscosity increases significantly. The particles with a larger aspect ratio lead to the larger increment in the viscosity, since they induce a larger resistance in a flow field. Copyright 2001 Academic Press.     

Synthesis of Polymeric Microspheres with Narrow Size Distributions Employing Microchannel Emulsification

Polymeric divinylbenzene microspheres (MS) of narrow size distributions were prepared by microchannel (MC) emulsification and subsequent polymerization. Using two types of MC plates, large MS with 9.2 μm diameter on average and 5.7% coefficient of variation, as well as small MS with 3.4 μm diameter on average and 7.4% coefficient of variation were prepared. The MS diameter can be controlled by the size of the MC. This method is advantageous for synthesizing polymeric MS of narrow size distributions because of its simplicity.