Particle size Aspect ratio

Toxicology. The toxicity of calcium silicate depends on particle size, aspect ratio, and amount of silica and respirable fiber. Synthetic nonfibrous calcium silicate is considered to be a nuisance dust. 

Figure 7. Wear rate as a function of initial counterface roughness for a series of carbon filled PTFE composites running in air against a steel counterface. The fillers are present at 10% by weight and the carbons differ in particle size, aspect ratio and surface chemistry. Little change in counterface topography is noted during the course of this experiment these carbons are not particularly abrasive towards steel. The evidence of a minimum in wear is not strong but it is consistent with other work. In this experiment there is a detectable inverse trend in the friction the lower the wear the higher is the friction. The symbols refer to carbons of different particle size and aspect ratio.

Structural characteristics include particle size, aspect ratio, crystallinity, bulk chemistry, defect structures, surface chemistry, surface structure and, in the case of its electrical behaviour, the density of electronic states in the interior and at the surface. Second, as introduced above, interactions between the nanoparticles and their environment may lead to a perturbation of the local structure or composition of the surrounding matrix material (Fig. 9.1c). Finally, the range of aggregation states of the primary nanoparticles needs to be considered, together with their distribution throughout the bulk (Fig. 9.1a). 

Talcs are either platy or acicular in particle shape. Thin platelet particles have aspect ratios varying from 20 1 to 5 1. Coarse particle sizes (10 to 75 im) are commonly used in these applications at loading levels of 5 to 30 percent. Fine talcs (1 to 10 im) are more expensive and require intensive dispersion processes. Platy grades enhance barrier properties and air, water, and chemical resistance. 

FIG. 5 Elongate polystyrene particles in the air-water interface. The particles are about 3 /mi long with a size aspect ratio of about 5. Courtesy of Prof. Jaime Ruiz-Garcia, Instituto de Fisica, Universidad Autonoma de San Luis Potosi. 

It depends on particle size, particle shape, aspect ratio, specihc gravity of the hller, and other properties of fillers. The following example illustrates this overah property of fillers. When polypropylene, having melt flow index of 16.5 g/10 min, was fllled with some mineral and cellulosic fillers, its MFl (in g/10 min) was as follows [2] ... 

The high nucleation efficiency of nanoparticles has been shown to be particularly advantageous for manufacturing microcellular foam (cell size <10 pm, cell density >10 cells/ctf) (Martini-Vvedensky and Waldman et al, 1982). The nucleation efficiency of the nanoparticles is dependent on the particle geometry, aspect ratio, dispersion, concentration, and particle surface treatment. These are discussed in detail in this section. The resulting changes in foam structure (bubble density, bubble size, and size distribution) and matrix properties have profound influence on the foam mechanical properties. 

Figure C2.17.2. Transmission electron micrograph of a gold nanoneedle. Inverse micelle environments allow for a great deal of control not only over particle size, but also particle shape. In this example, gold nanocrystals were prepared using a photolytic method in surfactant-rich solutions the surfactant interacts strongly with areas of low curvature, thus continued growth can occur only at the sharjD tips of nanocrystals, leading to the fonnation of high-aspect-ratio nanostmctures [52].

Wollastonite with an aspect ratio of 15 1 is useful as a replacement for asbestos and as a high-strength filler for plastics. The feed material with dgo of 45 [Lm was similarly ground. Beads of 0.3 mm gave faster grinding than 0.8 mm beads, and these corresponded to a bead-particle-size ratio of 19, confirming other results. 

There is a relationship that accommodates the wide range of fiber sizes and is independent of the composition or constitution of the fiber or fibrous material. The aspect ratio, or the relationship of the length to the thickness of the particle (length/thickness), can be calculated or estimated with relative ease. 

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