Particle shape irregular

Sieve analysis residue on 325 mesh - traces Particle shape irregular... 

Particle shape irregular Particle size, pm 4 Porosity high... 

Particle shape irregular, needle Crystal structure monoclinic... 

Particle shape irregular spherical spherical spherical... 

Particle shape irregular, needle Crystal structure monoclinic Oil absorption, g/100 g 60-120... 

Particle shape irregular Ciystal structure see below (a) Hegman tiness 2... 

Particle shape irregular or tubular Crystal structure hexagonal, hollow, single wall multiwall fibers ... 

This ideal case is rarely if ever encountered in practice in general there will be a distribution of particle sizes rather than a single size, and in addition there will usually be a range of particle shapes, many of them highly irregular. 

Because of the diversity of filler particle shapes, it is difficult to clearly express particle size values in terms of a particle dimension such as length or diameter. Therefore, the particle size of fillers is usually expressed as a theoretical dimension, the equivalent spherical diameter (esd), ie, the diameter of a sphere having the same volume as the particle. An estimate of regularity may be made by comparing the surface area of the equivalent sphere to the actual measured surface area of the particle. The greater the deviation, the more irregular the particle. 

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. 

Particle shape is also important. Disk-shaped as well as cylindrical-shaped conductors have a high response because large induced current loops are formed. Small randomly shaped conductors, such as those present in cmshed slag, also respond favorably. Sphere-shaped particles generate small-current loops, however, and do not have a high response. Multiple-current loops occur in conductors that have irregular bends, producing counteractive forces that tend to nullify each other. 

Particle shape also affects the sintering of a powder compact. Jagged or irregular shaped particles, which have a high surface area to volume ratio, have a higher driving force for densification and sinter faster than equiaxed particles. High aspect ratio platey particles, whiskers, and fibers, which pack poorly, sinter poorly. 

The majority of particles in the atmosphere are spherical in shape because they are formed by condensation or cooling processes or they contain core nuclei coated with liquid. Liquid surface tension draws the material in the particle into a spherical shape. Other important particle shapes exist in the atmosphere e.g., asbestos is present as long fibers and fly ash can be irregular in shape. 

So far the discussion has been limited to the case where the particle s charge is uniformly distributed. However, as discussed by researchers such as Goel and Spencer [89], and Hays [76,81], this might not be the case, especially if the particle is irregularly shaped. This can occur, as argued by Hays, if asperities on the particle prevent much of the surface area from contacting a neighboring... 

As a rule, the dispersed catalysts are polydisperse (i.e., contain crystallites and/or crystalline aggregates of different sizes and shapes). For particles of irregular shape, the concept of (linear) size is indehnite. For such a particle, the diameter d of a sphere of the same volume or number of metal atoms may serve as a measure of particle size. 

Spherical microparticles have been preferred in modem column technology since they form more hMiogeneous, stable and permeable column beds. Irregular microparticles are less expensive and still widely used, largely because in practice, it has not been shorn that their properties are significantly inferior. Particle shape may become more important as the particle size is reduced, and spherical microparticles are considered superior for particle dieuaeters less than 5 micrometers [33]. 

Recently, Rumpf (R5) has considered the forces of attraction between a plate and a sphere and between irregular shape particles. His conclusions are that the capillary bonds are relatively insensitive to the particle shape, but the van der Waals force of attraction is extremely sensitive. Although weaker in magnitude than the two aforementioned bonds, the electrostatic bonds may persist over long separation distances. 

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