Particles Shapes and Size Distributions

Filtration time. The filtration rate depends on the pressure difference, the solids content in the slurry, the particle shape and size distribution, the resistance of the filter medium to flow, and properties of the liquor. Observations show that the volume of the permeated liquor increases parabolically with time (see Fig. 5.3-26). 

Both permeability, K, and specific cake resistance, a, depend on the particle shape and size distribution. However, this relationship has not been recognized conclusively. Therefore, information on the crystal shape and size distribution, which can be obtained from experiments on crystallization, cannot be easily translated into the language of filtration characteristics. 

For a dust ignition to occur, the suspended solids concentration must lie between lower and upper limits which vary from material to material and are influenced by subtle factors such as particle shape and size distribution. From the standpoint of assessing safety hazards in commercial and industrial operations, the lower explosive limit is the more important one. The rationale of this statement is that, if the possibility of exceeding the lower limit in a powder-handling operation can not be completely ruled out, then a hazard must be recognized and appropriate measures taken. Over the... 

In many catalytic systems, nanoscopic metallic particles are dispersed on ceramic supports and exhibit different stmctures and properties from bulk due to size effect and metal support interaction etc. For very small metal particles, particle size may influence both geometric and electronic structures. For example, gold particles may undergo a metal-semiconductor transition at the size of about 3.5 nm and become active in CO oxidation [10]. Lattice contractions have been observed in metals such as Pt and Pd, when the particle size is smaller than 2-3 nm [11, 12]. Metal support interaction may have drastic effects on the chemisorptive properties of the metal phase [13-15]. Therefore the stmctural features such as particles size and shape, surface stmcture and configuration of metal-substrate interface are of great importance since these features influence the electronic stmctures and hence the catalytic activities. Particle shapes and size distributions of supported metal catalysts were extensively studied by TEM [16-19]. Surface stmctures such as facets and steps were observed by high-resolution surface profile imaging [20-23]. Metal support interaction and other behaviours under various environments were discussed at atomic scale based on the relevant stmctural information accessible by means of TEM [24-29]. 

In this section, various issues concerning solid particles are presented. The analysis covers the most important particle properties (surface area, particle shape and size distribution, mechanical strength, and density) as well as the behavior of a single particle in suspension (terminal velocity) and of a number of particles in fluidization state. Finally, the diffusion of molecules in a porous particle (diffusion coefficients) is also discussed. 

To allow for the influence of various particle shapes and size distributions within a defined sieve fraction, in lay-out calculations it is customary to employ an effective particle diameter, deff, as nominal size [32]. The diameter de is defined as the ratio of equivalent diameter A and a form factor j/. A is equal to the diameter of a sphere with a volume equal to the (average) volume of the particles, and ijj is the average ratio of the particle surface to the surface of a sphere of equal volume. 

A knowledge of the particle shape and size distribution is essential to the understanding of the behaviour of powders, as it will contribute to knowledge of the secondary properties of a powder, such as flow and deformation, which influence the processability. This topic is dealt with in detail in Chapter 6. 

It is important to note that in analyzing photometric measurements, it is necessary to use relevant constraints on the value of the complex refractive index and on the particle shape and size distribution. In the case of optically... 

Particle Shape and Size Distribution (DIN 66111, 66116, 66117, 66141, 66143-66145). Particles may have the following shapes (figures denote the aspect ratio) [4.14] ... 

Notably, however, if there is not enough plastic phase to fill all the voids among rubber particles then even though the plastic phase is a continuous phase it will not be a totally continuous phase and the resulting blend will have a very poor flow. From the known particle shape and size distribution, one can easily estimate the free volume in the rubber phase. The actual plastic concentration required to maintain plastic flow will be a few percentage points higher than this volume. 

Electron microscopy is a powerful technique for the characterization of Pd nanoparticles, and is capable of providing information of the morphology, topography and composition of the material under investigation. Here, we describe details of TEM and scanning electron microscopy (SEM), both of which are capable of providing detailed information about particle shape and size distribution. 

---