Determination of particle size

The particle size, dp, of a column may not be known at all, or information regarding it 

The factor 1000 applies for aU types of particle-packed columns if they are packed well and not clogged. 

A specific permeability of 4 x IO mm was calculated in Problem 18. To what particle diameter does this K° value correspond  

According to details supplied by the manufacturer, the mean particle size is about 5 pm (spherical silica). 

As already mentioned, K° is a function of particle shape. The factor 1000 applies only for well-packed columns and irregular particles, this figure being lower for spherical particles with a narrow size distribution (approximately 700). Nevertheless, it is possible to calculate the order of magnitude of particle size with this equation. 

1 Determination of Particle Size and Shape as well as Structure of Particle Packings 

It must be stressed that, in the context of this book, the treatment of methods of particle size analysis, which are of great importance for all unit operations of mechanical process technology, must be simple and can not be complete. The task of these chapters will be to provide an overview, to discuss specific problems and limitations of certain methods, and to point out suitable procedures for application in size enlargement. For more detailed information the extensive literature covering this field should be consulted. 

Normally, the particles within a system have different sizes. Therefore, a mean or average particle size characterizes the system only insufficiently. It is necessary to know the entire particle size distribution, particularly because the arrangement of particles in the system and, thus, the coordination number, which is very important for agglomeration, depend on the particle size distribution. 

The characteristics of disperse systems (see Section 1.1.2) are determined by geometrical parameters, i.e. linear dimensions, projection areas, surfaces, volumes, and, sometimes, angular dimensions. In addition, other physical characteristics, which do not directly represent particle size, may be used for the determination of these parameters. In such cases, a mathematical conversion into the desired geometrical dimension takes place. The term particle size analysis defines the experimental determination of particle characteristics and the statistical treatment of results. 

For another type of presentation the quantity found within a class of characteristics is referred to the total amount of the sample and the width of the class, which must not necessarily be constant from point to point. The distribution density q thus obtained can be presented graphically as a vertical bar over the dispersion characteristic. The horizontal dimension of the bar is equal to the class width. 

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Size. The precise determination of particle size, usually referred to as the particle diameter, can actually be made only for spherical particles. For any other particle shape, a precise determination is practically impossible and particle size represents an approximation only, based on an agreement between producer and consumer with respect to the testing methods (see Size measurement of particles). 

The determination of particle size and stmctural iaformation for fibers and polymers, and the study of stress, texture, and thin films are appHcations that are growing ia importance and can be examined with x-ray iastmments. 

Transmission electron microscopy is one of the techniques most often used for the characterization of catalysts. In general, detection of supported particles is possible, provided that there is sufficient contrast between particles and support - a limitation that may impede applications of TEM on well-dispersed supported oxides. The determination of particle sizes or of distributions therein is now a routine matter, although it rests on the assumption that the size of the imaged particle is truly proportional to the size of the actual particle and that the detection probability is the same for all particles, independent of their dimensions. 

Particle Size Measurement. The best way to evaluate an emulsion s stability is probably to measure its particle size distribution. A number of methods are available for droplet size determination (see Sec. VIII.A). Optical microscopy, although a time-consuming technique, is a direct way of measuring droplets larger than 1 pm. Nowadays, laser lightscattering, diffraction, and transmission methods are becoming popular for routine determination of particle size [151, 152],... 

Holmes, J. C., J. E. Hardcastle and R. I. Mitchell, The determination of particle size and electric charge distribution in cigarette smoke, Tobacco Science, 3 148-153 (1959). 

The usual techniques for the determination of particle sizes of catalysts are electron microscopy, chemisorption, XRD line broadening or profile analysis and magnetic measurements. The advantage of using Mossbauer spectroscopy for this purpose is that one simultaneously characterizes the state of the catalyst. As the state of supported iron catalysts depends often on subtleties in the reduction, the simultaneous determination of particle size and degree of reduction as in the studies of Fig. 5.10 is an important advantage of Mossbauer spectroscopy. 

The size range of commercial aerosols and the methods available for determination of particle size and for removing the particles from the gas are shown in Figure 1.50, which is taken from the work of Ashman. It may noted that the ranges over which the various items of equipment operate overlap to some extent, and the choice of equipment depends... 

E.W. Ciurczak, R.P. Tourlini and M.P. Demkowicz, Determination of particle size of pharmacentical raw materials using near infrared reflectance spectroscopy. Spectroscopy, 1, 36-39 (1986). 

J.L. Ilari, H. Martens and T. Isaksson, Determination of particle size in powders by scatter correction in diffuse near infrared reflectance, Appl. Spectrosc., 42, 722-728 (1988). 

Because PCS relies on the determination of the particle diffusion coefQcient, it is not a direct method for the determination of particle sizes. Information on the particle size can be obtained via the Stokes-Einstein equation... 

Determination of particle size in United States Pharmacopoeia (USP) grade aspirin... 

The experimental data of Espiard et al. (21,22), based on the AOT/ toluene/water/ammonia system, showed an increase in particle size with increase in R. This observation led the authors to conclude that the droplet size of the microemulsion water pool was a key determinant of particle size. The effect of R on particle size was also investigated for silica nanoparticles synthesized in AOT/ decane/water/ammonia microemulsions (31). No particles were observed below about R = 4. However, as R increased from 5 to 9.5, the particle size also increased, in agreement with the observations of Espiard et al. (21,22). As noted previously (see Figure 2.2.3), in this microemulsion system, free water pools do not become... 

Pollard (SO) found elutriation to be very successful for particles below 40 microns. The air is allowed to run for 30-minute intervals. When the sample remaining in the tube is less than 10% by weight of the previous one, the air flow is increased to remove the next size range. Excessive humidity and rough tube surfaces cause trouble. Tapping loosens the particles which might otherwise adhere to surfaces. Corcoran (20) gives a theoretical discussion of the determination of particle size, followed by a brief account of the elutriation process. 

A. Heim, Determination of particle size distribution of ground material, Rudy i Metale 38 (3) (1993) 74. 

The angular scattering approach is the principal aim of this work. The properties of the Lorenz-Mie intensity coefficients are treated in some detail in order to illustrate their utilization for the determination of particle size distribution, refractive index and number concentration. In a related paper the internal structure of polymer latex spheres is considered (8 ). ... 

Recently, a four-laboratory cooperative study has led to a comparison of the determination of particle size distribution by electron microscopy, quasi-elastic light scattering and wide angle light scattering (20). 

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