Characterization of particle shape

Finally, the necessity of multiangle measmement lies on the fact that except for spheres, the measmed ACF includes coupled signals from both translational and rotational motions. Without decoupling the two types of motions, further characterization of particle shape and size is impossible. In many cases, this type of data interpretation can only be accomplished by combining the ACF from several angles. A further explanation of this issue is provided in the next section. 

In reality, it is not so easy to use depolarized light scattering for quantitative characterization of particle shapes because of difficulties in both experiments and data analysis. The intensity of the depolarized component is often so weak that avoidance of stray light and leakage of polarized light can become serious praaical experimental problems. Also, a good model properly describing the particle is needed. 

Particle Size. Wet sieve analyses are commonly used in the 20 )J.m (using microsieves) to 150 )J.m size range. Sizes in the 1—10 )J.m range are analyzed by light-transmission Hquid-phase sedimentation, laser beam diffraction, or potentiometric variation methods. Electron microscopy is the only rehable procedure for characterizing submicrometer particles. Scanning electron microscopy is useful for characterizing particle shape, and the relation of particle shape to slurry stabiUty. 

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

In the course of further work on characterizing the MCC sols it was found that the CCC of a variety of salts varied both with the solids content and temperature. Investigation of these parameters forms the basis of the study. It will be shown that as a result of particle shape, concentration and surface characteristics, coagulation leads to a gel-like structure. On further addition of salt the coagulated gel-like structure aggregates into floes that are irreversible. In this paper, we outline the experimental parameters which lead to these phenomena and present some possible explanations. 

That no indication of the significant influence of particle shape on FFF elution behavior has been published until recently may be attributed to the fact that the majority of the approximately 500 papers so far published have reported on spherical or nearly spherical samples, and that the studies on the non-spherical samples focused only on sample fractionation rather than on a quantitative assessment of physicochemical quantities. This problem can be solved if fractions from FFF are further characterized, for example, by dynamic fight scattering or if an independent detector for diffusion coefficients is available. 

Particle behavior is a function of particle size, density, surface area, and shape. These interact in a complex manner to give the total particle behavior pattern [28], The shape of a particle is probably the most difficult characteristic to be determined because there is such diversity in relation to particle shape. However, particle shape is a fundamental factor in powder characterization that will influence important properties such as bulk density, permeability, flowability, coatablility, particle packing arrangements, attrition, and cohesion [33-36], Consequently it is pertinent to the successful manipulation of pharmaceutical powders that an accurate definition of particle shape is obtained prior to powder processing. 

The experiments consisted of three parts. In the first part, the characterization of minerals was explained by using x-ray diffractometer and electron microscope studies. Also, it was performed electrokinetic s studies of suspension. The effect of particle shape and size on the vacuum and pressure filtration of minerals has been investigated in the second part of the study. At the last part, the comparison of the particle shape and size effect on shear strength of the mineral filter cakes was performed. 

Following the progression of particle size analysis, so far we have gotten a perfect sample, uniquely characterized the particle size and done the statistical parameter estimates now we have the tools to look at actual data and methods of measurement. There are many methods for the characterization of particle size and shape however, in this section we will only include methods commonly used by researchers in tableting. The methods covered are microscopy, sieving, and laser diffraction. 

Lin CL, Miller JD. 3D characterization and analysis of particle shape using x-ray micro-tomography (xmt). Powder Technol 2(X)5 154(I) 6l-9. 

The detailed morphology (including overall particle shape, grain sizes and relative juxtapositions, and possible water inclusions) adopted by dried atmospheric particles probably depends on the temperature and the rate of evaporation. For these reasons, it cannot be certain that morphological features observed by TEM for particles dried by exposure to vacuum are the same as those adopted by particles dried by atmospheric processes. A critical need is the development of techniques capable of in situ characterization of particle morphology. Because the particles themselves are often no larger than 1 pm, the heterogeneity of their features occurs on the 10 to 100-nm scale. 

Oil absorption is a widely used parameter to characterize the effect of filler on rheological properties of filled materials. If oil absorption is low, the filler has little effect on the viscosity. The effect of particle shape on rheology should be considered... 

Thus, the concept of equivalent particle size gives a more nearly correct characterization of irregularly shaped particles. This equivalent size is more exact than the average particle size. 

The characterization of solid particles, most of which are, in practice, irregular in shape, is usually made by analysing the particle size (the measure of size most relevant to the particle property which is under investigation) and its distribution. Other characteristic properties of the solid material may be included in the measure of size determined, for example Stokes diameter combines size, density and shape all in one parameter, they can be characterized separately if necessary. British Standard BS2955 attempts to define shape qualitatively a quantitative measure of particle shape can be obtained indirectly by analysing two or more measures of particle size and looking at different shape coefficients that relate to those sizes. 

Methods for Direct Characterization of Particle Size and Shape... 

The question of particle shape is a complex problem and we are still at the sti e where we are developing methods to see if we can characterize adequately the range of shapes within a powder and their effect on the powder system and/or the aerosol system. It is becoming apparent that some complex problems will require more than one method of characterization thus if one was inhaling a complex soot particle the aerodynamic diameter which governs the penetration of the lung is one parameter whereas the fractal structure is another needed to assess the potential health hazard of the inhaled aerosol particle. 

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