Particle size from optical anisotropy effects in scattered light

An original light-scattering method often suitable for the case of anisotropic particles is explained. Two particular values of the scattering angle θ are needed: θ_m, the angular position of the minimum of the H_h component, and θ_o, the angular value for which H_h = V_v. This method has been successfully applied to the case of copolymer single crystals.     

Particle size distribution by design

Particle size distribution (PSD) is often specified in product design and can have a significant impact on plant operations. To meet the target PSD, a four-step procedure is proposed. For the desired PSD, a functional structure that identifies the required changes to the particles is constructed. Then, specific equipment as well as recycle streams are identified. Finally, alternative processes are evaluated using discretized population equations to determine process feasibility and to select the best option. The procedure is illustrated with three examples—the production of salt, alumina, and metronidazole tablets.     

Particle size analysis by automatic siever

Automation of the wet sieving process in an instrument for particle size analysis is described. A powder is consecutively subjected to three sieves of any selected meshes from 38 μm up and the resulting fractions are collected individually, including both the undersize and oversize, in a submerged filter. The initial filter weight and the weights of all collected fractions are determined separately and stored in the microcomputer memory. Upon completion of an analysis, the sieved fraction weights are recalled, the total sample weight is calculated, and results are presented as weight per cent. Completion of each sieving step is established by filter weight constancy according to prearranged programming. Upon completion of an analysis, the system backwashes the filter and re-establishes conditions for the next analysis. Tests for accuracy with a standard material and repeated testing for short and long-term reproducibility are included. Applicability to a variety of powders is demonstrated.     

Characterization of rubber particle size distribution of high-impact polystyrene using an image analysis method

Accurate characterization of high-impact polystyrene (HIPS) rubber particle size distribution has been achieved using an automatic image analysis system. The new method involves preparation of a microscope slide consisting of a dilute suspension of HIPS particles in a polymer matrix. Images of silhouetted rubber particles of true diameter are obtained using an image processor and particle size calculations can be made with a minimum of editing of the binary image. The new method provides measurement of true rubber particle diameters because the particles in the prepared slide are not swollen by any solvent.     

Particle size analysis by transmission fluctuation spectrometry with band-pass filters

The transmission fluctuation spectrometry (TFS) is a recently-developed method for real-time, online/inline particle analysis in two-phase flows, whereby the particle size distribution (PSD) and particle concentration can be measured simultaneously. This study presents a new technique of data processing to the fluctuating transmission signal. Instead of low-pass filters, band-pass filters are employed to improve the resolution of the measurement on particle size distribution. Based on the layer model, an analytical expression of the spectrum of the fluctuating transmission through a monolayer is derived and hence the spectrum of the fluctuating transmission through a 3-dimensional suspension is formulated. The comparison between simulation and theory at low concentrations shows a satisfactory match. Measurements on a mono-modal suspension are presented. It is found that the measurements using band-pass filters are of better resolution in the PSD than those with low-pass filters.     

The analysis of residence time distribution measurements using laguerre functions

The residence time distribution of a flow system can be determined from the response of the system to an arbitrary input, by a technique invoving Laguerre functions. This technique is convenient for digital computation, and is comparable in accuracy with other methods. The effects of the nature of the flow system, the arbitrary input, and the presence of noise are considered.     

Characterization of rubber particle size distribution of high-impact polystyrene using low-angle laser light scattering

A new application of low-angle laser light scattering has led to a new instrument capable of characterizing the rubber particle size distribution of high-impact polystyrene (HIPS) containing particles as small as 0.1 μ. Rubber particle size distributions of several HIPS resins have been characterized, and the particle size ranking of resins using light scattering parallels the ranking of resins using photomicroscopy. Several solvents have been employed to suspend the HIPS rubber particles for the scattering determination. Swelling of the rubber phase has been found to be relatively insensitive to variations in rubber phase crosslinking when methyl ethyl ketone is used to suspend the rubber particles. Particle swelling in methyl ethyl ketone does not detract from the usefulness of the light scattering method for HIPS rubber particle size characterization.     

Particle size analysis of dioctyl phthalate aerosols using the stöber aerosol spectrometer

Particle size distributions of nearly monodisperse dioctyl phthalate aerosols (dia. between 0–5 and 1–4 μm) have been determined using the Stöber aerosol spectrometer. The particle size distributions can be approximated very well by bimodal distribution functions. From a statistical analysis it turned out that the accuracy of the approximation is limited in case of small particles (dia. ～ 0·5 μm). This is due to evaporation of the particles during the analysis.The mean of the particle size distribution determined with the Stöber aerosol spectrometer was in fair agreement with the particle diameter determined with the higher order Tyndall spectrometer.     

Particle size analysis of plasticized PVC dispersion resins using the photometric centrifugal sedimentation method

There are many known methods for determining the particle size distribution of PVC dispersion resins. Most of these methods require that the resin be in an aqueous medium. PVC dispersion resins are used primarily in a plasticizer medium. The shearing action that takes place when the resin is mixed in plasticizer and the subsequent solvating action of the plasticizer affect the particle size distribution of the dispersion resin. It is advantageous to be able to determine the particle size distribution of the plasticized resin since it can affect various properties such as rheology, gloss and foam quality. It is the purpose of this paper to show that a fast zonal sedimentation technique can be used to analyze the less than 20 μ particle size fraction of a dispersion resin after it has been mixed in a plasticizer system. This can be accomplished in less than 90 minutes. This technique can be used to relate particular dispersion resin properties to the particle size distribution of the resin. The method can also be used as a quality control test.     

Particle shape and orientation in laser diffraction and static image analysis size distribution analysis of micrometer sized rectangular particles

Laser diffraction (LD) and static image analysis (SIA) of rectangular particles [United States Pharmacopeia, USP30-NF25, General Chapter <776>, Optical Miroscopy.] have been systematically studied. To rule out sample dispersion and particle orientation as the root cause of differences in size distribution profiles, we immobilize powder samples on a glass plate by means of a dry disperser. For a defined region of the glass plate, we measure the diffraction pattern as induced by the dispersed particles, and the 2D dimensions of the individual particles using LD and optical microscopy, respectively. We demonstrate a correlation between LD and SIA, with the scattering intensity of the individual particles as the dominant factor. In theory, the scattering intensity is related to the square of the projected area of both spherical and rectangular particles. In traditional LD the size distribution profile is dominated by the maximum projected area of the particles (A). The diffraction diameters of a rectangular particle with length L and breadth B as measured by the LD instrument approximately correspond to spheres of diameter Ø_L and Ø_B respectively. Differences in the scattering intensity between spherical and rectangular particles suggest that the contribution made to the overall LD volume probability distribution by each rectangular particle is proportional to A²/L and A²/B. Accordingly, for rectangular particles the scattering intensity weighted diffraction diameter (SIWDD) explains an overestimation of their shortest dimension and an underestimation of their longest dimension. This study analyzes various samples of particles whose length ranges from approximately 10 to 1000 μm. The correlation we demonstrate between LD and SIA can be used to improve validation of LD methods based on SIA data for a variety of pharmaceutical powders all with a different rectangular particle size and shape.     

A neural network-based soft sensor for particle size distribution using image analysis

Many industrial processes require on-line measurement of particle size and particle size distribution for process monitoring and control. The available techniques for reliable on-line measurement are, however, limited. In this paper, based on the captured surface images of randomly disarranged ore particles, the image uniformity was characterized. Particle size distribution was then investigated by applying a neural network-based modeling with the obtained image uniformity. The proposed soft sensor provides an improved prediction model and can be used for real time measurement of particle size distribution in the industrial operations.     

Determination of non-spherical particle size distribution from chord length measurements. Part 1: Theoretical analysis

In this paper, extensive theoretical studies are described on two important issues in translating a chord length distribution (CLD) measured by FBRM instrument into its particle size distribution (PSD) including PSD-CLD and CLD-PSD translation models for general non-spherical particles. Analytical solutions to calculate the PSD-CLD models for spherical and ellipsoidal particles are developed. For non-spherical particles, a numerical method is given to calculate the PSD-CLD model. The iterative non-negative least squares (NNLS) method is proposed in the CLD-PSD model, because of its many advantages converting measured CLD into its PSD, such as insensitivity to measurement noise and particle shape. The effectiveness of the proposed methods is validated by extensive simulations.     

散射法粒度分布测试中无约束反演的误差分析

激光散射法测量粒度分布技术近年来发展很快,其测量误差涉及散射理论及其反演计算,有关的理论研究还不充分。通过数值模拟,利用Chahine算法研究包含反演计算在内的系统误差。计算结果表明,光散射测量粒径不能通过简单的增加离散级数来提高测量精度,必须通过反演算法的改进来提高。     

Evaluation method for pore size distribution by using capillary liquid suction tests

In this paper, we introduce a method to evaluate pore size distribution using capillary absorption curves obtained by wicking methods. Its usefulness lies in its capacity to interpret experimental data by means of its reproduction, its capacity to predict them and its capacity to analyze work hypothesis. The theoretical basis for this study lies in the cylindrical capillaries model, to which two main considerations have been introduced: (a) the tortuosity, independent of pore volume, in which all the causes of the slowing down in liquid absorption with respect to the model are included, and (b) the influence of porous distributions, under the hypothesis that they adjust to simple mathematical functions. Numerous capillary absorption experiments were carried out and the data obtained from three of the tests, regarded as representative of the experiments developed, were reproduced by means of a simulation software in which the theoretical considerations described were implemented.     

A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements

A new analysis method has been developed for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. The method is based on a molecular model for the adsorption of nitrogen in porous carbon. It allows, for the first time, the distribution of pore sizes to be determined over both the micropore and mesopore size ranges using a single analysis method. In addition to carbons, this method is also applicable to a range of adsorbents, such as silicas and aluminas.     

Extension of the measuring range in size exclusion chromatography to higher molar mass by use of a light scattering detector

A new method for the extension of the measuring range of size exclusion chromatography coupled with light scattering (SEC/LALLS) to higher molar mass is presented. This method uses the fact that the light scattering signal can often be detected already at considerable smaller values of the elution volume (i. e. higher values of molar mass) than the concentration signal; furthermore, it takes into account the peak broadening effect in SEC. This procedure is tested for the case of a logarithmic normal distribution and a most probable distribution of molar mass. In the case of polypropylene with a logarithmic normal distribution (M?_w = 420 000, M?_n = 99 000), the range of molar mass covered by SEC/LALLS can be extended by a factor of about 10; with a most probable distribution (M?_n = 100 000), the attainable extension in molar mass assumes a factor of about 2.     

Radiative transfer modeling of filter-based measurements of light absorption by particles: Importance of particle size dependent penetration depth

We present new physical models to interpret the response characteristics of filter-based measurements of aerosol light absorption. They were motivated by a recently found particle size dependence of a systematic bias in absorption measurements that cannot be interpreted by any models reported thus far. A theory of particle filtration by fibrous filter is applied to reproduce the penetration depth of particles into a filter matrix, and the light transmissivity of the matrix is calculated by the use of radiative transfer theory for plane-parallel layers. Optical properties of individual layers are calculated from microphysical properties and the number density of filter fibers and deposited particles. The size-dependent systematic bias in absorption measurement is successfully explained by the particle size dependence of penetration depth into a filter matrix. In practice the physical models developed here are useful for selecting operating conditions and filter matrices for instruments with fewer systematic biases.     

Particle size monitoring in dense suspension using ultrasound with an improved model accounting for low‐angle scattering

The inherent ability of ultrasonic wave to propagate in dense and opaque suspensions makes it a desirable method for online measurement of particle size distribution in industrial operations. The ability of ultrasonic attenuation spectroscopy to determine particle size distribution has been extended to dense suspensions of particles lying predominantly in the intermediate wave propagation regime at the measurement frequencies. This was achieved by accounting for the effect of detector size and shift in the frequency spectrum under dense conditions in the theoretical model and deconvolution algorithm, respectively. The proposed modifications enable the application of this technique in various industrial processes requiring in situ and real‐time measurement of particle size distribution such as crystallization, mineral processing and food processing. © 2010 American Institute of Chemical Engineers AIChE J, 2010